TIME Aging

You Asked: Do Brain Games Really Improve Memory?

Illustration by Peter Oumanski for TIME

Unhand the crossword: it's not your golden ticket to a lifetime of quick wit and perfect recall

Games sure seem like a good way to work your brain out, but don’t put your stock in Sudoku. “They target very specific cognitive abilities, but they don’t transfer to clarity of thinking, problem solving, planning—all the complex skills that really matter,” explains Dr. Sandra Bond Chapman, chief director of the Center for Brain Health at the University of Texas at Dallas and author of Make Your Brain Smarter.

When it comes to keeping your brain real-world strong, research has shown–over and over again–two activities to be worth your time. The first is aerobic exercise, says Dr. Karen Li, head of Concordia University’s laboratory for adult development and cognitive aging.

By bolstering your cardiovascular fitness and blood circulation, exercise nourishes your brain with the nutrients and oxygen it needs to perform optimally, Li says. But physical activity offers more than just brain fuel. “Some brain regions and functions seem to benefit more than others,” she explains–specifically the frontal lobe, responsible for high-level skills related to complex processes like multitasking. “That tells us aerobic exercise helps the brain work more efficiently.”

Whether you enjoy running, speed walking, gardening or hiking, “as long as you sweat a bit and your heart rate goes up, that’s what your brain needs,” Li adds. Chapman agrees. “Skip the Sudoku and get out and exercise,” she says. (The Centers for Disease Control and Prevention recommends all adults get at least 150 minutes of moderate-intensity aerobic exercise a week.)

Along with physical activity, your brain needs mental stimulation to stay hale and fit. And when it comes to mental stimulation, novelty is important, Li explains. Here’s why: The more you use your mind to perform a task—whether it’s cooking your favorite dish or driving to the supermarket—the less effort your brain requires to complete that task. “If you feel like your brain’s on autopilot most or all of the time, that’s an indication that you need to increase the challenge a little bit,” she says.

One of the best ways to do that is to stay socially active, Li says. “Following and contributing to a conversation requires a lot of mental prowess.” Visiting intellectually invigorating places, like museums or cultural centers, and learning new skills are also great ways to keep your brain in shape. Even mixing in some variety when it comes to your favorite activities—like trying out a new recipe or cooking technique—will keep your mind off autopilot.

But there’s a catch. “It’s important that you feel genuine interest in these activities,” Li says. Practicing a foreign language for 30 minutes a day is a good way to challenge your brain, but if you feel meh about one day speaking fluent French, your mind won’t benefit as much as it would from something that truly excites or interests you.

If museum visits or learning new languages doesn’t float your boat, Chapman offers an alternate way to fire up your idling brain. “Challenge yourself to think in top-down, complex ways as you go about your day,” she recommends. When you watch a television show or read an article (like this one), pause once you’ve finished to really dissect the information you’ve just encountered. “Zoom out, then zoom in,” Chapman says. Start as broadly as you can (this is a health article) and work your way down (about the brain) until you’ve gotten to the nitty gritty—things like themes or lessons you could take away from what you’ve just seen or read (surely, too numerous to list).

“People take in a lot of information—probably more than we ever have before—but it’s not making us smarter because we’re not spending much time making sense of it,” Chapman says. “Try to push yourself out of your mental comfort zone by asking what about the information matters.”

This is especially important for older retired adults who aren’t faced with the everyday intellectual challenges presented by work or school. “We’re all going to be living longer,” Chapman says. “Along with aerobic exercise, engaging your brain in complex ways is absolutely necessary to keep your mind sharp in the second half of life.”

TIME Exercise/Fitness

You Asked: Should I Eat Before or After a Workout?

Illustration by Peter Oumanski for TIME

Experts answer the great exercise question of our time

Short answer: Both.

Long answer: How and when to fuel your body is the same for all exercisers to some extent, but your routine may warrant a few nutritional tweaks, says Dr. Nancy Cohen, head of the department of nutrition at the University of Massachusetts.

“In general, you’ll want to eat a meal high in carbs and protein and low in fat roughly three to four hours before you exercise,” Cohen says, whether you’re trying to shed pounds or build muscle. Carbohydrates supply your body with the glycogen it needs for your yoga session, gym visit, or jog. Skimp on carbs, and your muscles will sputter when called on to perform, she says.

If you’re trying to lose weight, it may seem weird and counterproductive to eat a carb-heavy meal before you hit the gym. But complex carbohydrates like beans, lentils, whole grains and starchy vegetables will provide exercise fuel plus nutrients and fiber. Unlike refined carbohydrates—things like white bread, cookies, soft drinks, or many pre-packaged foods—complex carbs won’t expand your personal equator or supercharge your appetite, research shows.

Cohen recommends avoiding fat in your pre-workout meal because it slows down your digestion. But eating protein supports your muscles. “During and after exercise, your muscle cells break down and rebuild,” Cohen explains. The right proteins contain the amino acids your muscles need to complete that cellular rebuilding process.

Complete protein packages include animal sources like chicken or lean beef, since they have all those amino acids, Cohen says. Grains like quinoa and bulgur as well as beans and some vegetables also contain protein, though probably not the “complete” kind. But if you eat a variety of those food sources, you can skip the meat and still get all the amino acids you need, she adds.

As for post-workout food, Cohen suggests eating or drinking more protein an hour or two after lifting weights for bodybuilders and athletes. But despite what you’ve heard, it’s not necessary (or healthy) to pound a massive protein shake the second you stop pumping iron.

According to Dr. Rob Danoff, an Aria Health System physician with a focus on sports medicine and nutrition, your body—and especially your kidneys—can only synthesize so much protein. Research suggests roughly one gram of protein per kilogram of body weight is plenty to maximize muscle growth. By that measure, for a person who weighs 175 pounds, 80 grams of protein all day is enough.

One large chicken breast or cut of red meat can contain 60 grams of protein or more, so slamming a huge protein shake after a workout will only inundate your kidneys with protein it can’t handle and your muscles don’t need, Danoff says. Apart from the risk of kidney damage, there’s evidence that overloading your body with protein can contribute to an imbalance in the acidity of your blood, which in the long run could lead to bone weakening. “It’s a myth that we need all this protein,” Danoff says. “More isn’t always better.”

In your workout-food focus, don’t forget water. If you exercise first thing in the morning, Cohen says dehydration is a big concern because you’ve probably passed much of the night without a sip of H2O. “Your whole cellular metabolism is dependent on fluid,” she says. And everything from your workout performance to your mood and mental acuity will suffer if you’re parched.

TIME You Asked

You Asked: Why Do Mosquitoes Always Bite Me?

Illustration by Peter Oumanski for TIME

You’re covered with itchy red welts while your friends seem blissfully unbitten. What’s the deal with that?

First of all, it’s not in your head. Mosquitoes really do prefer some people to others, says Dr. Jonathan Day, a medical entomologist and mosquito expert at the University of Florida. And that time your grandmother told you your skin was just sweeter? There’s some truth to that, Day says. “Some people produce more of certain chemicals in their skin,” he explains. “And a few of those chemicals, like lactic acid, attract mosquitoes.” There’s also evidence that one blood type (O) attracts mosquitoes more than others (A or B).

Unfortunately, your genes dictate your blood type and the chemical makeup of your birthday suit. Genetics also determine several other factors that could make you an object of blood-sucking affection for your local mosquito population, Day says. Maybe the most important: Your metabolic rate, or the amount of carbon dioxide (CO2) your body releases as it burns energy.

Mosquitoes use CO2 as their primary means of identifying bite targets, Day says. Why? “All vertebrates produce carbon dioxide, so what better way could there be for a mosquito to cue in on a host?” And while it’s true that you can moderate your metabolic rate through diet and exercise, you can only change your metabolism so much, Day says.

“Pregnant women and overweight or obese people tend to have higher resting metabolic rates, which may make them more attractive to mosquitoes,” he explains. Also, drinking alcohol or physically exerting yourself raises your metabolic rate—and also your appeal to winged biters, he adds. (Exercising before grabbing a beer and heading outside = asking for trouble.)

While CO2 detection is the primary technique mosquitoes and other blood-sucking bugs use to spot hosts, they also rely on secondary cues to differentiate you from cars, decaying trees, and other CO2-producing objects. And you can control some of those secondary cues, Day says.

For example: Dark clothing is more attractive to mosquitoes than light oufits. Why? “Mosquitoes have problems flying in even a slight wind, and so they keep close to the ground,” Day explains. Down there, they spot hosts by comparing your silhouette to the horizon. Dark colors stand out, while light shades blend in, he says. At the same time, lots of motion distinguishes you from your surroundings. So if you’re moving around a lot or gesturing, you might as well be shouting, “Hey, mosquitoes! I’m right here, ladies!” (Only the females bite, Day says.)

Obviously, you’re not going to spend the summer sitting stock-still in a white suit. So what are the best ways to avoid itchy bites? Day recommends protective clothing, which doesn’t mean baggy jeans and long-sleeved sweatshirts. “Lots of the lightweight, breathable fabrics made for athletes or fishermen are woven tightly enough to protect you from bugs,” he says.

If your summer style isn’t negotiable—or for those parts of your body you can’t cover up—Day recommends a mosquito repellant with 15% DEET. Just make sure to follow the label’s instructions for safe application. “Spray it into your hands and then rub it on your skin to avoid inhaling it,” he says. “That’ll protect you for around 90 minutes.”

Also, mosquitoes usually feed at dawn and dusk when the wind tends to die down and the humidity rises, Day explains. If you can stay indoors at those times, you’ll avoid bites. A good fan pointed in your general vicinity will also do a great job of keeping the bugs away. “Mosquitoes can’t fly in a breeze faster than 1 mile per hour,” Day says.

If all that fails, hug a bite-free buddy. Maybe some of his mosquito-repelling skin chemicals will rub off on you.

TIME Aging

You Asked: Can Computers Really Ruin My Eyes?

Illustration by Peter Oumanski for TIME

You spend most of the day staring at a computer, and your tablet or smartphone lull you to sleep at night. What does all that digital screen time do to your eyes?

From sore eyes and blurred vision to headaches, doctors have a catch-all term for any screen-induced discomfort: “Computer vision syndrome,” says Dr. Joshua Dunaief, an ophthalmologist and macular degeneration researcher at the University of Pennsylvania. Dunaief says the specific causes of computer vision syndrome (CVS) are numerous, from improper reading glasses to an overly bright screen. But in most cases, any eye issues you’re experiencing stem from two root issues. Either your eyes are dried out, or they’ve become too fatigued to see properly.

“There are tiny muscles inside your eyeball that change the shape of your eye’s lens in order to bring whatever you’re seeing into focus,” Dunaief explains. After hours of sitting in front of your computer screen, those muscles can grow tired from focusing on a single fixed point. “In some cases, those muscles become so fatigued that your eyes can no longer focus,” Dunaief adds. He says research has also shown that when reading or working online, people tend to blink less. That can lead to dry eyes, tearing, or a burning sensation, he says.

While you’re not powerless to combat these problems (more on that in a minute), Dunaief says these issues are typically short-lived—meaning they go away within a few hours if you abandon your computer. But are there any serious, long-term dangers associated with digital screens?

“Possibly,” Dunaief says. “There’s evidence that bright light can damage your retinas irreversibly. That might mean staring at a computer screen that is very bright could damage your eyes.” He says there’s also some experimental evidence indicating regular exposure to computer-strength light could be damaging in similar ways.

Sitting too close to your computer screen (or holding your cell phone very near to your face) could also potentially lead to some vision problems, explains Dr. Joan Portello, an associate professor and researcher at the State University of New York School of Optometry. “A lot of people don’t realize this, but when you’re viewing something really close, that’s when your eyes are working the hardest—much harder than when you’re looking at something far away,” Portello explains.

Both she and Dunaief say there’s some evidence that students who spend many hours hunched over textbooks tend to become nearsighted. (Some Chinese schools have started employing metal desk bars to keep kids from lowering their heads too near to their study materials.) “Kids who play outside a lot tend to have better distance vision,” Portello adds. “And heavy computer use could turn out to cause some similar issues to this close textbook reading.” Like Dunaief, Portello says it’s too early to say how bad long-term computer use is for your eyes.

One thing is crystal clear: Computers aren’t going anywhere. So what can you do to safeguard your sight? First and foremost, proper eyewear is essential—especially if you’re older than 40, when reading small print tends to become troublesome for most people, Dunaief says. “Your reading glasses aren’t made for your computer,” he explains. Ditto for your regular spectacles. “An optometrist can fit you for glasses made specifically for computer use that will make things easier on your eyes.”

Dunaief also recommends dimming your computer screen and moving it as far away from your eyes as comfort and readability allow. Enlarging the font, closing blinds, and turning down the lights in your office to prevent glare can also help keep your eyes safe, he explains.

Portello says eye drops or artificial tears can help, as long as you consult with your eye doctor first about which type will work best for you. She also recommends sticking to the 20-20-20 rule. “Every 20 minutes, look away from your screen at something 20 feet away for 20 seconds,” she advises. Why? This gives your eye muscles a rest and helps ward off fatigue and strain. Focusing on something even farther away is just as good, she adds. “And while you’re at it, try to blink as much as you can to keep your eyes moist.”

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?

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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.

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