TIME Mental Health/Psychology

You Asked: What’s the Best Bedtime?

Illustration by Peter Oumanski for TIME

The earlier the better? 11 PM? Sundown? Sleep experts say it’s not that simple. But there is a time range you should shoot for if you’re questing for a perfect night’s sleep

Every hour of sleep before midnight is worth two after midnight. Your grandparents (and great grandparents) probably adhered to that creaky adage. “The mythology is unfortunate, because there’s no pumpkin-like magic that occurs,” says Dr. Matt Walker, head of the Sleep and Neuroimaging Lab at the University of California, Berkeley. And while nothing special happens to you or the quality of your sleep at the stroke of midnight, many do wonder: What’s the best time to go to bed?

Walker says your sleep quality does change as the night wears on. “The time of night when you sleep makes a significant difference in terms of the structure and quality of your sleep,” he explains. Your slumber is composed of a series of 90-minute cycles during which your brain moves from deep, non-rapid eye movement (non-REM) sleep to REM sleep. “That 90-minute cycle is fairly stable throughout the night,” Walker explains. “But the ratio of non-REM to REM sleep changes.”

He says that non-REM sleep tends to dominate your slumber cycles in the early part of the night. But as the clock creeps toward daybreak, REM sleep muscles in. That’s significant, because some research has suggested that non-REM sleep is deeper and more restorative than lighter, dream-infused REM sleep—though Walker says both offer important benefits.

What does this have to do with the perfect bedtime? The shift from non-REM to REM sleep happens at certain times of the night regardless of when you go to bed, Walker says. So if you hit the sack very late—at, say, 3 AM—your sleep will tilt toward lighter, REM-heavy sleep. And that reduction in deep, restorative sleep may leave you groggy and blunt-minded the next day.

That’s unfortunate news for nightshift workers, bartenders, and others with unconventional sleep-wake routines, because they can’t sleep efficiently at odd hours of the day or night, Walker says. “The idea that you can learn to work at night and sleep during the day—you just can’t do that and be at your best.” Your brain and body’s circadian rhythms—which regulate everything from your sleeping patterns to your energy and hunger levels—tell your brain what kind of slumber to crave. And no matter how hard you try to reset or reschedule your circadian rhythms when it comes to bedtime, there’s just not much wiggle room. “These cycles have been established for hundreds of thousands of years,” Walker explains. “Thirty or 40 years of professional life aren’t going to change them.”

When it comes to bedtime, he says there’s a window of a several hours—roughly between 8 PM and 12 AM—during which your brain and body have the opportunity to get all the non-REM and REM shuteye they need to function optimally. And, believe it or not, your genetic makeup dictates whether you’re more comfortable going to bed earlier or later within that rough 8-to-midnight window, says Dr. Allison Siebern, associate director of the Insomnia & Behavioral Sleep Medicine Program at Stanford University.

“For people who are night owls, going to bed very early goes against their physiology,” Siebern explains. The same is true for “morning larks” who try to stay up late. For either type of person—as well as for the vast majority of sleepers who fall somewhere in between—the best bedtime is the hour of the evening when they feel most sleepy.

That means night owls shouldn’t try to force themselves to bed at 9 or 10 if they’re not tired. Of course, your work schedule or family life may dictate when you have to get up in the morning. But if you can find a way to match your sleep schedule to your biology—and get a full eight hours of Z’s—you’ll be better off, she adds.

Both she and Walker say your ideal bedtime will also change as you age. While small children tend to be most tired early in the evening, the opposite is true for college-aged adults who may be more comfortable going to bed around or after midnight. Beyond college, your best bedtime will likely creep earlier and earlier as you age, Walker says. And again, all of this is set by your biology.

Siebern suggests experimenting with different bedtimes and using sleepiness as your barometer for a best fit. Just make sure you’re rising at roughly the same time every morning—weekdays or weekends. It’s fine to sleep an extra hour on your days off. But if you’re getting up at 6:30 during the workweek and sleeping until 10 on weekends, you’re going to throw off your sleep rhythms and make bedtime more challenging, she says.

TIME Diet/Nutrition

You Asked: Is Coffee Bad For You?

Illustration by Peter Oumanski for TIME

For years, your morning joe got a bad rap from health experts. But newer research suggests coffee may actually be good for you—if you follow the rules

“I gave up coffee” is a refrain of the health conscious. But should it be? The idea that coffee is a dangerous, addictive stimulant springs mostly from 1970s- and 1980s-era studies that tied the drink to higher rates of cancer and heart disease, explains Dr. Rob van Dam, a disease and nutrition expert at Harvard School of Public Health who has examined coffee and its health effects. According to van Dam, that old research didn’t do a great job of adjusting for a person’s cigarette habit or other unhealthy behaviors.

But newer, better-designed research paints a more benign picture of your favorite eye-opener. Van Dam and his colleagues analyzed health and diet data on roughly 130,000 adults spanning 24 years. They found no evidence that drinking coffee increases your risk of death from cancer, cardiovascular disease, or other causes. That was true even for people who knocked back 48-ounces of coffee a day. In fact, there was some indication that regular coffee drinkers might enjoy a slight drop in mortality risk, van Dam says.

The idea that your java could actually deserve a health halo would have shocked doctors a few decades ago. But van Dam’s study is only one in a wave of new research sure to please coffee fans. Coffee has been linked to lower rates of type-2 diabetes, a reduced risk for some cancers, and protection against Parkinson’s disease. Other research links coffee to improved memory, mood and energy levels.

The drink could even help shield you from a deadly form of skin cancer. How? The caffeine in coffee may interact with a type of “repair gene” that plays a role in the development of basal cell carcinoma, says Dr. Jiali Han, a disease researcher at Indiana University, Indianapolis, who coauthored the coffee-and-skin cancer study. Han says it’s also possible that coffee’s antioxidant compounds could account for the drink’s anti-cancer benefits—an explanation you’ll come across a lot when reading about coffee’s benefits.

But before you start swigging your java by the gallon, van Dam warns that there remain reasons to be careful. There’s evidence that pregnant women might want to limit morning caffeine fix because of an admittedly small correlation between coffee intake and miscarriage. (There is research showing that moderate coffee drinking is perfectly safe, making it a judgment call for expecting moms.) There are also reports hinting that people with cholesterol issues may have more problems if they drink some kinds of coffee. Compounds called cafestol, present in coffee beans, appear to raise LDL cholesterol—though paper filters eliminate most of those compound, making it more of a concern with French press and espresso-style brews. And of course, if you’re drinking so much that you’re unable to sleep or your heart races, that’s a bad thing too, van Dam adds.

But if you’re in good shape and enjoy coffee? “For most people,” van Dam says, “black coffee is a healthy, non-caloric beverage choice.” And it should go without saying that the benefits conferred to coffee do not extend to mocha-flavored “coffee drinks” or other sugar-loaded concoctions.

“Coffee is a highly complex beverage with hundreds of compounds,” van Dam says, which means it affects people differently. Van Dam doesn’t recommend people who don’t already drink the stuff start now, but if you love it, can tolerate it, and it isn’t messing with your sleep? Bottoms up.

TIME Diet/Nutrition

You Asked: Can Water Go Bad?

Illustration by Peter Oumanski for TIME

Does drinking old water make you sick?

That depends, says Dr. Kellogg Schwab, director of the Johns Hopkins University Water Institute. As soon as you take a sip, your lips and mouth introduce microorganisms into your H2O. Combined with the ambient temperature in your home or office, and sunlight streaming into your windows, those microorganisms could start to multiply pretty quickly, Schwab says.

“If you have clean water in a clean glass, you’re fine for a day or two,” he says, adding that almost all tap water in the U.S. contains chlorine additives that will kill small communities of microorganisms. But if you’ve ever swigged a sip of day-old water from bedside your bed or on your desk and wondered why it tastes funny, that’s because after about 12 hours it goes flat and, as carbon dioxide from the air interacts with the H2O in your glass, it slightly lowering its pH. “But it’s most likely safe to drink,” Schwab adds.

He says reusing the same dirty glass day after day will raise you risk of exposure to some unfriendly bacteria—especially if someone else is sipping from your vessel and mixing his or her mouth microorganisms with yours. But assuming you grab a new cup every few days? “You’re probably not going to have a problem,” Schwab assures, adding that, “This is far from the top of the list of public health concerns.”

One possible exception: Touching the rim of your glass with dirty fingers—especially if you (or whoever unloaded the dishwasher) forgot to wash up after using the bathroom. There are lots of different sickness-causing bacteria in human waste, and if you handle your glass with dirty hands, those bacteria could make their way into your water, Schwab warns.

But what about that plastic water bottle on the floor of your car? Heat and plastic are a bad combination, he stresses. “A chemical called bisphenol-A, or BPA, along with other things used to manufacture plastic can leach into your water if the bottle heats up or sits in the sun,” he explains. BPA is a hormone disruptor that research has tentatively linked to several health hazards, including heart disease and cancer. Schwab says the types of plastic used for bottling water aren’t meant to be washed or refilled, so use them once and recycle them. Or better yet, use refillable containers made of metal or glass.

When it comes to storing water for long periods, the answer is “Yes,” your H2O can certainly become unsafe to drink, says Zane Satterfield, an engineer scientist with the National Environmental Services Center at West Virginia University. “Most experts will tell you tap water has a shelf-life of six months,” Satterfield says. “After that point, the chlorine dissipates to the point that bacteria and algae start to grow.” That growth will speed up if you store your water in a warm or sunny spot—or in a glass container that hasn’t been thoroughly washed or sealed, he adds.

If you’re a doomsday hoarder with giant vats of pre-packaged water in your basement, you should know that will last at least a year. But after 12 months you’re best off swapping out what you have for fresh stores, Satterfield advises. “You’ll see that some of the water will evaporate during that time, which is proof that the plastic isn’t impermeable,” he explains.

If you want to play it safe when it comes to water that’s been stored for long periods, Satterfield says adding a few drops of plain, unscented bleach and waiting 30 minutes will make your water safe to drink. (Specifically, that’s four drops per gallon, he adds.) Good to know in case of an apocalypse—zombie or otherwise.

TIME You Asked

You Asked: Why Are People Addicted to CrossFit and Other Brutal Workouts?

Why are people addicted to Crossfit?
Illustration by Peter Oumanski for TIME

Psychologists explain the appeal of extreme health behaviors

CrossFit. Bikram. Ultra-marathons. When it comes to the latest exercise trends, nearly all have one thing in common: They take relatively anodyne workouts—lifting weights, yoga, running—and crank the intensity up to 11. If previous generations stuck to the health motto “everything in moderation,” modern America has shifted emphatically toward “go big or go home”—even if some doctors and scientists believe those behaviors approach (and sometimes cross) the line into dangerous territory. So what gives?

The obvious answer is that these programs tend to produce big results in a hurry, says Dr. Juliana Breines, who researches health psychology at Brandeis University. Looked at that way, you could chalk up these workout trends to a Netflix-ified, want-it-now ethos within American culture. But plenty of research suggests the appeal of intense workouts goes far beyond impatience or a desire for quick results.

A new study appearing in the Journal of Consumer Research concludes feeling as though parts of your life have slipped out of your control spurs a craving for effortful activity. “What we’re finding is that when people are feeling a loss of control, they’re particularly likely to go for these high-effort things like very intense workouts because it makes them feel empowered,” says study co-author Dr. Keisha Cutright, an assistant professor of marketing at the University of Pennsylvania.

Along with the demands of work and family, your income, age, and even the economy could be contributing to the sense that you’re losing control of your world, Cutright explains. When it comes to an activity like CrossFit, “You feel like you’re in charge of the desired outcome,” she explains. “You find a certain amount of control over your life, and that feels good.”

Dr. Brock Bastian, a psychologist at the University of Queensland in Australia, has conducted dozens of experiments examining the psychological interconnectedness of pain and pleasure. He says extreme exercise may be a form of “functional” self-punishment—a way of beating yourself up to alleviate some sense of guilt or shame you derive from another part of your life. One of his experiments asked people to recall a time when they’d acted immorally. Following those thoughts, these study participants held their hands in icy water longer than did people who had not been primed to recall a moral transgression. Similarly, “Going on a hard run is perhaps a convenient way to make ourselves feel better after we’ve behaved badly,” Bastian explains. “It makes us feel like the scales of justice have been rebalanced.”

His research also demonstrates that if you feel good about yourself, enduring physical pain can enhance your enjoyment of—and sense of entitlement to—guilty pleasures. Not only that, but inflicting pain on yourself raises your stature in the eyes of others, he adds. Suffering through a grueling endurance race or difficult workout can make you seem tolerant, persistent, and strong in the minds of your friends and colleagues.

On a darker note, there’s also some research that suggests low self-esteem may drive some people to punish themselves though harsh diets or physically demanding exercise, says Breines, the Brandeis health psychologist. “People who are lower in self-esteem may be more likely to choose to suffer based on the belief that they deserve to suffer, and because suffering is more consistent with their negative self-views,” she says, adding that this belief may explain some people’s attraction to extreme diet and exercise regimens.

Of course, there is also the possibility that a healthy appetite for challenge and the physical release of a tough workout is all that’s at play for some people. In the end, a complicated mix of some or all of these factors may explain the drive to push workout routines to the limits.

“I’ve met many people who fashion their daily life, work, and relationships completely around their extremely rigorous exercise routines, and who persist exercising despite injuries,” says Dr. Anna Keski-Rahkonen, who researches public health issues at the University of Helsinki in Finland. But Keski-Rahkonen says it’s difficult to draw a line between a compulsive behavior and something more nefarious. “Currently, it’s still quite unclear where normal behaviors end and problematic behaviors begin.”

Consider all of this food for thought the next time you double down on your boot-camp class pack.

TIME Cancer

You Asked: Is Sunscreen Safe — and Do I Really Need It Daily?

Is sunscreen bad for me?
Illustration by Peter Oumanski for TIME

Tons of you Google it. Our experts have the answer

Google sunscreen and toxic and see what you find. Claims that titanium dioxide is hazardous? Claims that you need vitamin D, and a little unprotected sun can give you that? Claims that chemical sunscreen can turn boy fish into girl fish? Let’s settle this for once and … for now, at least.

First thing’s first. There are two kinds of sun blockers — the physical kind, like zinc and titanium dioxide, and the chemical kind, like oxybenzone and its many cousins. They work in vastly different ways, the former blocking or “scattering” the sun’s rays (literally), and the latter causing a chemical reaction that is said to prevent damage from the sun’s UVA and UVB rays.

Start looking into it and two topics tend to come up again and again. The first surrounds titanium dioxide or zinc oxide — but only in their nanoparticle form — which means ultra-fine specs of material used in sunscreens to block or “scatter” the sun’s rays. Some scientists have voiced concern that nanoparticles may be small enough to slip past your skin’s defense barriers and into your bloodstream. Those concerns have grown louder since a recent study — albeit in rodents — found that mice injected with titanium dioxide nanoparticles developed inflammation, a marker of cell distress that has been linked to lots of terrible things that happen in the body, including aging — and cancer.

These concerns do not extend to sunscreens that contain titanium dioxide and zinc in non-nano form—although those are becoming harder to find.

The second source of concern involves other nonnano sunscreen chemicals, which work by absorbing the sun’s ultraviolet radiation as opposed to reflecting it. More animal studies have hinted at ways in which some of these chemicals could cause damage to a person’s endocrine — hormone — system. That’s the worrisome news and if you want to avoid risk, many experts contend, you are better off with nonnanoparticle forms of the physical sun blockers.

The good news: there just isn’t much hard data showing that applying these chemical sunscreens to your skin can lead to health problems, says Dr. Henry W. Lim, chairman of the Dermatology Department at Henry Ford Health System in Detroit.

Lim points out that many of the animal studies at the root of sunscreen concerns involve injecting or inhaling the chemicals, not rubbing them on your skin. “As of today there are no recorded health issues associated with sunscreen’s proper use,” he says.

But, in almost the same breath, Lim says there may still be reasons to worry about sunscreen. Specifically, he says spray-on sunscreens could present some unique dangers. That’s because, unlike lotions spread on the skin, spray-ons can be inhaled. “That could lead to very different types of risks not associated with creams,” he says, adding that the FDA is in the process of investigating the potential dangers of spray-on products. (The FDA is also, after much delay and pressure, investigating the introduction of new sunscreen ingredients that have been on the market in Europe for some time. Stay tuned for more on the bill that could change that.)

Looking past the possible dangers of sunscreen use, the benefits are far less nebulous: 1 in 3 cancers diagnosed worldwide is a skin cancer, according to the American Cancer Society. And up to 95% of malignant melanomas are caused by excessive sun damage, found research from the International Agency for Research on Cancer. “The risks associated with sun exposure are well mapped and well understood, and we have proof that using sunscreen lowers these risks,” Lim stresses.

“Sunburns are bad. There’s just no way around it,” says Kerry M. Hanson, a chemist at the University of California, Riverside, who has studied sunscreens extensively and has also worked with sunscreen manufacturers. “Protecting oneself from sunburn is critical to prevent skin cancers later in life,” she says. And to protect against sunburn, Hanson says sunscreen is proved to be effective — if it’s applied properly.

A recent study from the University of Queensland in Australia found people who followed proper sunscreen-application practices on a daily basis developed roughly 50% fewer melanomas than those who were left alone to use (or not use) sunscreen as they saw fit. Similar research efforts have uncovered proof of sunscreen’s effectiveness at blocking the development of squamous-cell and basal-cell cancers as well.

Unfortunately, Lim says many people don’t rub on nearly enough of the stuff to protect themselves. You need to spread on 1 oz. — or about the amount that would fill a shot glass — to safeguard your whole body for just a couple hours, he says. And that’s assuming you’re not sweating or swimming, in which case you need to apply more frequently.

In the end, he says the greatest danger of sunscreen may be that it provides people with a false sense of security against the sun’s dangers. “Just because you rub some on in the morning doesn’t mean you’re safe spending all day in the sun,” he says.

TIME You Asked

You Asked: Will Eating Before Bed Make Me Fat?

What to eat at night
Illustration by Peter Oumanski for TIME

You’ve been told eating before bed is a no-no. But a little pre-slumber snack can help you sleep more soundly without packing on pounds—if you reach for the right foods.

Especially if you tend to eat dinner a few hours before bedtime or you’re very active (or both), snacking before bed will help stabilize your blood sugar levels during the long, meal-less night, explains Stephanie Maxson, senior clinical dietician at the University of Texas’s MD Anderson Cancer Center.

Why should you care about blood sugar? As most diabetics know, blood sugar and its attendant hormones can supercharge or deflate your appetite and energy levels, as well as mess with your body’s efforts to store or burn fat. “Having low blood sugar in the morning will cause a person to feel sluggish and make it more difficult to get out of bed,” Maxson explains, adding that low blood sugar could also wake you up or otherwise disrupt your sleep in the middle of the night.

Ideally, you want to encourage stable blood sugar levels for optimal health, which will be tough to do if you’re going 10 or 12 or 14 hours without eating, Maxson says. (This is one reason she and many other nutrition experts underscore the importance of eating breakfast.)

“It’s such a big myth that you don’t need any energy for sleep,” adds Cassie Bjork, a registered dietician and founder of HealthySimpleLife.com. Not only can the right bedtime snack provide the fuel your body needs to burn calories while you sleep, but a little grub also calms the release of hunger hormones that tell your body to store fat, Bjork explains.

That said, a pint of ice cream isn’t going to do you any favors. Instead, you should be reaching for complex carbohydrates like whole wheat bread, non-starchy vegetables, popcorn, and fruit, Maxson says. These foods break down slowly, and so help stave off the blood sugar spikes or crashes that could mess with your sleep or appetite, she explains. For athletes, adding a protein like turkey or chicken to a bedtime snack can help with muscle repair during the night while also providing a hit of an essential amino acid called tryptophan, which is beneficial for sleep, Maxson says.

And don’t shy away from a little fat, which can further slow the absorption of carbohydrates into your system, Bjork says. Some avocado or peanut butter—or a splash of melted butter on your popcorn—can help if you frequently wake up hungry or tired.

Just be sure to avoid things like chips, cookies, cereal, or pretty much any traditional dessert food, advises Dr. Joan Sabaté, a professor of public health and nutrition at Loma Linda University. Because fiber and other digestion-slowing nutrients are typically stripped away from these foods during their preparation, your body absorbs them quickly and they tend to cause quick spikes in your blood sugar, which can make it tough for your to sleep, Sabaté explains.

Anything featuring caffeine—yes, that includes chocolate—is also a bad idea at bedtime, Maxson says.

TIME Infectious Disease

Spacing Out Kids’ Vaccines Can Hurt Their Health, Experts Say

Girl getting immunization
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All those shriek-inducing pokes may seem excessive but the rewards of following national vaccination guidelines far outweigh the risks, experts say

“Like any parent, I don’t like to see my child get a shot,” says Dr. Michael J. Smith, a pediatrician at the University of Louisville who has studied immunizations and developmental health outcomes among kids. “But these vaccine schedules are in place for a reason.” Smith compares skipping or postponing one of your child’s vaccinations to not buckling him or her in during a car ride. “You never know when you’re going to get hit. And if you delay or space out your child’s shots, not only are you putting your kids at risk, but you’re putting other people’s kids at risk too.”

The urgency of Smith’s warnings are borne out in the recent outbreaks of measles and pertussis, diseases that had been almost totally eradicated in the U.S. but have made a frightening comeback since the turn of the century—right around the time two now-discredited scientific papers suggested a possible link between vaccines and autism. Dozens of subsequent studies have demonstrated there are no links between vaccinations and autism. But while stats show most parents understand the importance of immunizing their kids, research from the University of Michigan indicates plenty of moms and dads—roughly 1 in 4—worry that current immunization guidelines may overburden their babies’ tiny immune systems.

The Centers for Disease Control and Prevention (CDC) currently recommend that all healthy babies be vaccinated against 12 different diseases or viruses during the first two years of life. That’s compared to eight back in the early 1990s. Recently added to the list are vaccinations against potentially deadly illnesses like hepatitis and chicken pox.

But while the number of vaccines (and needle pricks) has grown during the last two decades, the amount of antigen in those shots, which is the substance that triggers a response from your child’s immune system, has plummeted, Smith explains. “The actual burden on your child’s immune system is far lower that it was 10 or 20 years ago, even though kids now receive more shots,” he says. That’s credited to advances in protein science and a better understanding of the way diseases and children’s immune systems interact.

In an effort to provide some answers for concerned parents, Smith and his colleagues looked at kids’ scores on tests related to motor skill, verbal memory, attention span, and several other neuropsychological factor to see if vaccine timing had any impact—good or bad—on a child’s brain development. His research shows kids vaccinated on time score the same or better than children who receive their vaccinations late or not at all.

Related research from Canada looked specifically at the immunization decisions made by parents of children diagnosed with autism. “Our study found that roughly 60 percent of parents who had a child with autism delayed or declined vaccinations for a later-born child,” says Dr. Jessica Brian, a developmental psychologist at the University of Toronto. According to Brian’s research, those children who did not receive their shots on time or altogether were slightly more likely to develop autism. “I don’t want to suggest that vaccines offer some protection against autism,” she says. “But our data show that there’s no increased risk of autism among kids who are vaccinated on time.”

Brian, Smith and other vaccine researchers repeatedly point to the Internet as a source of misinformation and, in some cases, unsubstantiated fear mongering when it comes to vaccines. Not uncommon are conspiracy theories involving pharmaceutical companies and the CDC. But travel overseas, and the picture changes slightly.

In Europe, where some diseases were never eradicated as thoroughly as they were in the U.S., health officials say there isn’t as much “too much, too soon” concern among parents when it comes to immunizations. Still, European moms and dads do harbor fears about potential vaccine side effects, says Niklas Danielsson, deputy head of the vaccine-preventable diseases program for the European Centre for Disease Prevention and Control. Danielsson says the “unprecedented success” of vaccination programs has created a generation of young parents who aren’t familiar with the reality of something like a measles outbreak, so they’re focus is on a shot’s rare risks as opposed to its many proven benefits.

The lingering presence of diseases in other countries is one of the big reasons having your children vaccinated on time is so important, says Dr. Simon Hambidge, a professor of pediatrics and epidemiology at the University of Colorado. “We live in a world of international travel, and people are coming into our country all the time who may be carrying these diseases,” Hambidge says. “Unfortunately, the vast majority of the new outbreaks we’re seeing involve unvaccinated children.”

Hambidge has looked closely at one possible vaccine side effect that has parents worried: seizures. The CDC recommends that all healthy infants receive their first measles vaccination between the ages of 12 and 15 months, and some research has linked the measles vaccine to higher rates of febrile seizures. Though frightening for parents, seizures of this type are relatively common and almost never cause lasting damage, Hambidge explains. “About one in 2,000 to 4,000 kids will experience one of these febrile seizures after receiving the measles vaccine,” he says. “But we found that that seizure rate rises to one in 1,000 or 2,000 if the measles vaccine is given late, or between 16 and 23 months of age.” Hambidge says this is just one example of how a slight deviation from the CDC’s vaccination schedule can put your child’s health at risk.

“The risk of measles is far, far more serious than the risk for febrile seizures,” Hambidge says. “Even if your child is unlucky enough to have a seizure after a vaccination, these seizures are short-lived and don’t lead to any long-term issues, while measles is a life-threatening disease.”

Despite the overwhelming amount of research and real-world evidence that points to the reliable safety of vaccines, experts acknowledge that parents will continue to worry about the chemicals and additives in immunization shots. To those who have doubts, Dr. Smith says, “Vaccines are one of the most rigorously tested and effective health products on the planet. Nothing involving them is done lightly.”

And when it comes to the CDC’s recommendations regarding vaccination schedules, he adds, “As a pediatrician and as a parent, if my family’s on vacation and we have to put off my daughter’s doctor visit, I get anxious each day that she goes unvaccinated. I think the timing is that important.”

TIME

You Asked: Are All Calories Created Equal?

Are all calories equal?
Illustration by Peter Oumanski for TIME

Kale or corn dogs, bananas or beer, a calorie is still a calorie. At least, that’s what dieters have been told for the past half-century. Now, experts don't agree

“By and large, we’ve been taking an accounting approach to weight loss,” says Dr. David Ludwig, a professor of nutrition at the Harvard School of Public Health. By that he means, health scientists have traditionally focused on the number of calories coming in versus the number of calories going out. But there are a lot of problems with that approach, he says. For one thing, it’s really tough to accurately keep track of your daily calorie intake. “Being off by just 100 calories a day could add up to a hundred pounds over a lifetime,” he says.

If burning more calories than you consume would keep you skinny, a low-fat diet should be the answer to all your diet prayers. That’s because, compared to protein or carbohydrates, fat contains roughly twice the number of calories, ounce for ounce. But Ludwig says low-fat diets have proved ineffective when it comes to losing weight. “Mediterranean or low-carbohydrate diets outperform a low-fat diet every time, and that wouldn’t be true if calories were the only measure that mattered,” he adds. (Mediterranean diets and others like the now-trendy Paleo diet are both high in fat, comparatively speaking.)

In reality, Ludwig says the body responds differently to calories from different sources. “Your weight is regulated by a complex system of genetic factors, hormonal factors, and neurological input, and not all calories affect this system the same way,” he explains.

As for fat: “Some naturally high-fat foods are among the most healthful we can eat in terms of promoting weight loss and reducing risk for diabetes and heart disease,” he explains, listing off foods like nuts, avocados, and many types of fish. “If you’re counting calories, you would want to eat these foods sparingly because they’re dense in calories. But they’re also very filing.”

Refined carbohydrates, on the other hand—like those found in white bread, cookies, crackers, and breakfast cereals—raise your blood’s level of the hormone insulin, which signals to your body that it needs to store fat cells. Also referred to as high-glycemic foods, these refined carbs pass through your digestive system quickly—which is why you can eat a whole bag of potato chips and feel hungry 15 minutes later, Ludwig says.

Dr. Richard Feinman, a professor of cell biology at the State University of New York Downstate Medical Center, compares insulin to a faucet handle. The more your blood’s amount of the hormone rises, the more the faucet opens and the more fat your body stores.

Feinman has looked at calories from the perspective of thermodynamics—or the laws that govern heat and energy. Like Ludwig, he says the idea that calories from different macronutrient sources would have the same effect on your body is silly. Put simply, it doesn’t make sense that “a calorie is a calorie” because your body uses the energy from different foods in a variety of ways, Feinman explains.

The big lesson here is that people need to look at food as not just a collection of calories, experts say. By cutting out refined carbs and eating more protein and healthy fats, which help you stay full without triggering the storage of fat cells, “You can work with, as opposed to against, your body’s internal weight-control systems,” he says. “That will make weight loss more natural and easy.”

The best part: You can put away the calculator. No more calories counting.

TIME You Asked

You Asked: Is Hot Yoga Good For You—And For Weight Loss?

Hot Yoga
Illustration by Peter Oumanski for TIME

Devoted hot yogis swear by the activity’s many benefits. Others roll their eyes and wonder: Is it even safe to work out at 104 degrees? Here's what the experts say

Start poking around for hard science on Bikram or “hot” yoga, and you’ll find something curious: There’s not much of it. “Considering how popular this is, it’s pretty shocking that our study is one of the very first published research efforts on the subject,” says Dr. Brian L. Tracy, an exercise scientist at Colorado State University.

Tracy and his team have conducted two experiments on the physical effects of Bikram yoga, which involves completing a strict series of poses over a period of 90 minutes in a room heated to 104 or 105 degrees. The first experiment included healthy (but sedentary) young adults with no yoga experience. After eight weeks and 24 Bikram sessions, Tracy says the study participants showed some modest increases in strength and muscle control, as well as a big improvement in balance. They also achieved a slight drop in body weight.

“To be honest, we were pretty surprised by the small size of the weight change, because when you’re in the Bikram studio you feel like you’re working really hard,” Tracy says. “And remember, these were people who didn’t regularly exercise before the study. We were expecting a bigger drop.”

For his follow-up experiment, Tracy hooked up experienced yogis to equipment designed to measure their heart rates, body temperatures, and energy expenditures during a typical Bikram session. That new data helped explain some of those disappointing body-weight findings: While heart rate and core temp climbed significantly (but not dangerously) during the 90-minute session, the participants’ metabolic rates—or the amount of calories their bodies burned—were roughly equivalent to those of people walking briskly.

“I think the immediate reaction is disappointment if you’re a Bikram fan,” Tracy says, adding that, if you’ve spent time reading about the activity online, you might assume you’d be shedding up to 1,000 calories per session. “But that’s not the case,” he says. His research shows men burn an average of 460 calories, while women work off about 330. “I think the heat and the difficulty of the postures combine to alter your perception of the intensity of the exercise,” he explains. On the other hand, one part of your body is getting a major workout, Tracy says. “Heart rates are quite high for the amount of work you’re doing. Quite high.”

Is that something you should worry about, though? “Potentially,” says Dr. Kim Allan Williams, president-elect of the American College of Cardiology. When you’re hot, your heart pumps large volumes of blood to the vessels in your skin where, through a process called convection, sweat is produced. “And it’s actually not the sweat, but the sweat’s evaporation that helps cool you off,” he explains. “Sweat does not evaporate efficiently in those conditions,” he adds.

What does this have to do with hot yoga? The humidity in Bikram yoga studios is supposed to be kept at 40 percent. But in reality, Tracy says it’s tough to know how often that goal is achieved or maintained. As the humidity climbs and your heart keeps working to cool you off, you’re sweating out minerals like potassium and sodium, along with H20, Williams says. “It’s the same for athletes working out in the middle of summer,” he adds. “You have to be mindful of the heat and humidity.”

To protect yourself, both Tracy and Williams say hot yoga practicers need to pay close attention to their bodies. Feelings of light-headedness, nausea, confusion, or muscle cramping—either during or after a yoga practice—are all signs that you need to take a break. That’s especially true for inexperienced yogis, whose bodies aren’t acclimated to the rigors of hot yoga, Tracy explains.

Williams also stresses the importance of hydration and nutrient replacement. “You can’t sweat out a bunch of minerals and then replace them with water alone,” he says. Dangerously low levels of potassium, sodium, and other electrolytes contribute to those scary health risks mentioned above.

Left unanswered are questions about the long-term effects of hot yoga practice, or how people with heart defects or other health conditions might react to the strenuous conditions, Tracy says.

Sweaty bodies aside, most hot yoga fans also praise the activity’s mental and psychological benefits. And a growing pile of research on yoga suggests the practice—and not just the hot varieties—may help lower stress while improving pain management and emotion regulation in ways similar to meditation.

“This isn’t something we’ve studied directly, but I do think there’s an element of mindfulness in Bikram yoga instruction,” says Emily Lindsay, who researches stress and mindfulness meditation at Carnegie Mellon University. Focusing your attention on your breathing and body posture can anchor you in the present moment and foster mindfulness, Lindsay explains. Yoga practice can also provide moments of peace without interruption from your cell phone, email, or life’s other routine distractions. It’s not farfetched to think that these components could offer yoga practitioners some psychological benefits, Lindsay says.

“Millions of people do it, and there aren’t just one or two anecdotal stories about how Bikram changes people’s lives,” Tracy says. “So there has to be something to it.”

TIME Diet/Nutrition

A Chemical In Coffee, Fries, and Baby Food Linked to Cancer, Report Says

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The research isn’t conclusive. But lab evidence suggests a type of chemical found in starchy foods cooked at high temperatures—as well as coffee and some baby foods—could promote the growth of cancer cells

The crispy brown crust that forms on your french fries or toast? Those are hot spots for a chemical called acrylamide, which forms when the sugars and amino acids found naturally in foods like potatoes and cereal grains are cooked at temperatures above 150 degrees. It’s present in cookies, crackers, coffee and some baby food that contains processed bran. And according to a new report from the European Food Safety Authority (EFSA), it’s a public health concern.

So should you worry?

Here’s what scientists know now: Lab studies involving animals have shown that diets loaded with acrylamide can cause DNA mutations that increase the risk of tumor growth and the spread of cancer cells. But studies involving people have produced “limited and inconsistent evidence” when it comes to the ties between acrylamide and cancer, the EFSA says.

While people exposed to the chemical in an industrial setting have suffered from nervous system issues like muscle weakness or limb numbness, that has little to do with your diet. “That was through inhalation and skin exposure to high levels of acrylamide at the work place, not food consumption,” stresses Marco Binaglia, a scientist who helped draft the EFSA report.

Binaglia says that, for now, it’s not possible for him or other health scientists to make diet recommendations. “We’ve identified a possible model of action that explains how acrylamide could damage DNA in a way that leads to cancer-producing cells.” But more study is needed to produce specific dietary guidelines, he adds.

For example, Binaglia says the EFSA’s coffee research only looks at acrylamide content, and does not take into account all the other possibly beneficial chemicals and compounds found in your morning joe, for instance. “A lot of questions cannot be answered right now,” Ramos adds. Similarly, the American Cancer Society (ACS) says that, based on available research, “It is not yet clear if acrylamide affects cancer risk in people.”

Despite all the unknowns, if you want to reduce your potential risk by cutting out the chemical from your diet, the ACS recommends boiling potatoes, which results in less acrylamide formation than roasting or frying. They also suggest lightly toasting your breads—no dark spots.

And as for acrylamide in coffee, says Luisa Ramos, another researcher who helped draft the report: “It’s usually found at higher levels in light roasts because it forms during the first minutes of roasting and then degrades as the roasting process continues.”

Ramos says choosing darker coffee roasts may lower your exposure. And, for concerned parents, baby foods that don’t contain processed cereal grains should have lower levels of the chemical.

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