TIME neuroscience

Here’s a New Trick to Help Babies Learn Faster

Surprise them. Not by jumping out of a closet but by challenging her developing notions about the world, and avoiding the same-old same-old

We know that babies like new things. Present them with something they haven’t seen before and they’ll gravitate toward it, touch it, bang it around, put it in their mouths. It’s all part of the learning process so they can build a database of knowledge about the world around them.

But for babies to really learn about how the world works, it takes more than novelty. In a series of experiments with 11 month olds published Thursday in the journal Science, researchers at Johns Hopkins University found that surprising information—things that went against babies’ assumptions about concepts like gravity and the solidness of objects—forms the seed for future learning.

Aimee Stahl, a PhD candidate in the department of psychological and brain science at Johns Hopkins University, and her colleague Lisa Feigenson conducted a set of experiments with 110 infants to tease out this effect of surprise in how babies learn. The studies began with the assumption that babies are born with certain core knowledge about how the world works — that objects are solid so other things can’t pass through them, for example, or that dropping things causing things to fall rather than float.

MORE: Naps May Help Babies Retain Memories, Study Finds

First, Stahl challenged these concepts with some babies by strategically using a screen to hide a wall as they rolled ball. When they lifted the screen, some babies saw the ball stopped in front the wall, as they would expect. Other babies, however, saw the ball on the other side of the wall. When both groups were then presented with something entirely new to learn — associating a squeaking sound with a new toy — the babies who saw the contrary event (the ball on the other side of the wall) learned to link the sound to the new toy more quickly than those who saw the expected event (the ball on the correct side of the wall).

To ensure that the babies weren’t just enthralled with the novelty of the new toy, Stahl and Feigenson then repeated the experiment, except this time during the testing phase they played a different, rattling sound instead of the squeaking noise. The learning scores in the first experiment were still higher than those in the second version, strongly suggesting that the babies were actually making new connections and learning something about the objects, rather than just paying attention to the new-ness of them.

MORE: How to Improve a Baby’s Language Skills Before They Start to Talk

This was supported by the other experiments Stahl and Feigenson conducted, in which babies tried to find an explanation for the contrary results; for the balls that appeared to melt through the solid wall, they bounced and banged the balls to verify their solidity. For situations in which objects seemed to defy gravity and float, they dropped them. “It seemed like they were seeking an explanation to the kind of surprising events they witnessed,” says Stahl. “If it was just novelty that was attracting them, they wouldn’t be so specific in the way they handled the objects.”

These are the first experiments to test the idea that learning involves more than just exploring new things; Stahl’s results indicate that surprising or contradictory information helps them to confirm and test their knowledge, and try to explain events that seem to go against what they know.

“It raises exciting questions about whether surprise is something educators, parents and doctors can harness to enhance and shape learning,” says Stahl. She’s exploring, for example, how surprise can help in learning even with older children in more naturalistic environments, outside of artificial lab experiments. “Our research shows that when babies’ predictions about the world don’t match what they observe, that signals a special opportunity to update and revise their knowledge and to learn something new.”

Video: Johns Hopkins University Office of Communications; Len Turner, Dave Schmelick and Deirdre Hammer

TIME Cancer

How Fish Oil Makes Chemo Less Effective

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Tetra Images—Getty Images/Tetra images RF

“You lose at least half the effect of the chemotherapy” because of the fish oil, the scientist says

It wasn’t something Dr. Emilie Voest and his colleagues expected to see, but in their labs, they found a disturbing connection between fatty acids and their effect on chemotherapy drugs. Fatty acids—the good fats found in fish like mackerel, salmon and sardines—turn out to work against chemotherapy agents in cancer patients, according to research published Thursday.

Voest, medical director of the Netherlands Cancer Institute, stumbled upon this in 2011 when he found that certain stem cells in mice with cancer that he was studying also produced fatty acids — and that these fats neutralized the effects of chemotherapy. Would the same occur in cancer patients, he wondered, who took fish oil supplements or ate fatty fish?

MORE: Omega 3s Reality Check: Are We Over-Exaggerating Their Benefits?

In a series of experiments described in JAMA Oncology, he and his team established that after getting fish oil supplements from commercially available brands, mice showed higher blood levels of the fatty acids for several hours. The same happened when healthy volunteers took one of two doses of fish oil supplements from three popular brands. Even at the lower dose, which was the recommended daily amount of fish oil of 10 ml (about two teaspoons), levels of fatty acids in the blood of the volunteers doubled on average after several hours.

In mice with tumors who were also given chemotherapy, the fish oil supplements suppressed the anti-tumor effects of the chemotherapy; “You lose at least half the effect of the chemotherapy” because of the fish oil, says Voest.

MORE: Fish Oil Fail: Omega-3s May Not Protect Brain Health After All

He stresses that there’s still a lot about the connection between fish oil and chemotherapy drugs that isn’t known. The effect seems to be limited to certain cytotoxic chemotherapy agents that work by damaging the DNA of tumor cells; some more targeted chemo agents won’t be as affected by the fatty acids. Voest also notes that fish oil supplements, because they aren’t regulated by the U.S. Food and Drug Administration, vary widely on how much fatty acids they contain. What’s more, the content of fish oil can change from pill to pill or drop to drop.

“I don’t want patients who had chemotherapy in the past and it didn’t work to think that it was their fault because they took fish oil,” he says. “Obviously there is a balance between how sensitive a tumor is to chemo v the resistance-causing effect of fatty acids.”

MORE: Omega-3 Supplements Don’t Lower Heart Disease Risk After All

In his studies, Voest also analyzed the effects of fish oil from eating fish among healthy volunteers without cancer; mackerel and herring — even at servings slightly smaller than a deck of cards — were two that contributed to the biggest peaks in fatty acid levels in the blood several hours later. Salmon and tuna only led to negligible blips in this particular study.

The one thing Voest and his team could not do was test the effects of fish oil on cancer patients. Because mouse studies showed that fish oil could compromise the effects of chemotherapy, he says it was “unethical in our view to demonstrate that chemo combined with fish oil was less effective than chemo alone,” he says, since some patients may be receiving an intentionally inferior therapy.

“These authors went beyond theory and showed with animal data that there may be an impact,” says Dr. Don Dizon, co-director of gynecologic oncology at Massachusetts General Hospital and a spokesperson for the American Society of Clinical Oncology, who was not involved in the research. “And in the absence of human data, we need to take this quite seriously and discuss these results with our patients.”

With most supplements, Dizon says, it’s difficult to counsel patients since there isn’t even data from animal studies to guide doctors, as there now is with fish oil. Dizon says he advises patients getting chemo to avoid taking antioxidants, for example, but only because in theory, chemotherapy causes oxidative stress and the supplements may counter that effect. “But I have absolutely no data to support that.”

But between the animal studies and the tests on healthy human volunteers, he’s more comfortable advising patients about fish oil. “I think I will be using this clinically, and discussing it with my patients,” says Dizon, especially since he relies on a DNA-damaging chemotherapy agents to treat the cancers he sees. Voest also says he’s advising patients to avoid taking fish oil or eating large amounts of fish on the day before, the day of and the day after receiving chemo. That may be difficult for some, especially since cancer websites advise patients to take fish oil as a way to reduce side effects from chemotherapy. But, as Voest says, “now we know why.” It may be that the fish oil is hampering the anti-cancer effects of the drugs instead of mitigating their adverse effects.

Voest is planning on studying the biological link between fatty acids and chemotherapy drugs more carefully. He’s also launching a clinical trial to see if a compound that inhibits the function of fatty acids might work to improve chemotherapy’s effect in patients taking fish oil and getting chemo.

TIME medicine

This Is What Binge Watching TV Does to Your Health

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Cultura/Liam Norris—Getty Images

Every hour spent sitting in front of the TV can increase your risk of diabetes

It’s easy—and tempting—to settle in for a marathon session with your favorite TV show, but that indulgence may come back to haunt you.

In a study of people at higher risk of developing diabetes, researchers say that every hour spent sitting can increase the risk of developing the metabolic disorder by 3.4%. For a day-long binge, that could be as much as a 30% higher risk. “With streaming TV, you can watch a program continuously; instead of watching just half an hour once day a week, you can watch a whole season in a day, so we expect to see increases in sitting to continue,” says Andrea Kriska, an epidemiologist at the University of Pittsburgh and senior author of the paper on the effects of TV on diabetes risk in the journal Diabetologia.

Kriska is part of the Diabetes Prevention Program Research Group, which found that people who spent more time sitting, whether in front of the TV or at work, were more likely to develop diabetes than those who sat less, regardless of how much they exercised.

MORE: Sitting Is Killing You

The group started with the population of people at higher risk of developing diabetes who were enrolled in the Diabetes Prevention Program. Some were assigned to exercise at least 150 minutes at a moderate level each week and change their diet with the goal of losing 7% of their body weight. Others were given the diabetes drug metformin, and another group was given a placebo. In 2002, after more than three years, those who adopted the lifestyle changes lowered their risk of developing diabetes by 58%, compared to 31% for those taking the drug.

More and more data suggest that to reduce disease, it’s not just enough to exercise more; you have to sit, less too. The scientists wanted to see what role, if any, sitting played in this reduction. Did being more physically active lead to helping people be less sedentary? And did time spent sitting have any connection with the rate of diabetes?

MORE: Sitting Can Increase Your Risk of Cancer By Up to 66%

“What we found was yes, and yes,” says Bonny Rockette-Wagner, from the department of epidemiology at Pittsburgh. “There is an independent effect of sitting behavior on diabetes incidence that does not have to do with physical activity. It’s an independent, additional effect.”

The researchers asked the 3,232 people in group how much time they spent sitting at work and how much time they spent watching TV, as a proxy for their total sedentary time. They also asked them about their leisure time physical activity and measured their blood glucose levels. After three years, the lifestyle group spent fewer hours sitting than the metformin and placebo groups, despite the fact that sitting less was not a specific goal of the program. And the more time they spent off their chairs, the lower their risk of going on to develop diabetes.

MORE: An Hour of Exercise Can Make Up for a Day of Sitting Down

The results suggest that efforts to help high-risk people avoid diabetes should include a goal of sitting less. That’s what Kriska and Rockette-Wagner are starting to do in their community sessions in which they teach people about the Diabetes Prevention Program. Instead of focusing exclusively on the target of 150 minutes of exercise each week, they’re asking people to think about sitting less, starting by spending a few minutes fewer on the couch each day and building up to becoming more active.

MORE: Sitting All Day Isn’t As Bad If You Do This

The researchers admit that simply sitting less won’t replace being physically active, but after so much focus on getting sedentary people to move, getting them to think about sitting less may be just as productive.

TIME Cancer

How We’re Failing at Preventing Cancer

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JUAN GARTNER—Getty Images/Science Photo Library RF Illustration of cancer cells in middle of dividing

We’ve made lots of progress in preventing cancer, but still have a long way to go in convincing people to drop the most prevalent cancer-causing habits

You have to know your enemy in order to defeat it, and in cancer’s case, we know quite a bit about how to keep tumors from growing. But how well are we exploiting this knowledge?

The latest report, published Wednesday morning, from the American Cancer Society lays out the major risk factors for cancer, along with the screening strategies we have in place and documents whether people have been avoiding risky behaviors and complying with screening guidelines.

The results, says Stacey Fedewa, director of risk factors and screening surveillance and one of the co-authors, are mixed.

MORE: The Cancer Gap

When it comes to tobacco use, the largest preventable cause of cancer, rates of smoking have declined, from 23.5% in 1999 to 17.8% in 2013. But there are still pockets of the country, both geographically and demographically, where rates remain close to what they were 10 years ago. In West Virginia, for example, 27.3% of adults smoked cigarettes, and 22.7% of American Indians lit up. About 22% of high school graduates smoked, compared to 5.6% of those with a graduate degree. Smoking tobacco increases the risk of lung, mouth, larynx, esophagus, stomach and other cancers

The survey also found that smokeless tobacco and e-cigarettes are also becoming popular, particularly among younger people. These forms of tobacco have been linked to higher rates of oral, pancreatic and esophageal cancer. People aged 18 to 24 years were twice as likely to use smokeless products like chewing tobacco and snuff than older adults.

The creep of tobacco use into younger cohorts is concerning, since studies show that the younger smokers start, the harder it is for them to quit. In fact, the ACS study found that even one in 10 cancer patients smoked nearly a decade after their diagnosis.

MORE: 66% of People Diagnosed with Cancer Survive At Least 5 Years

Fedewa says that obesity is also connected to a number of cancers, including breast, colon, kidney, pancreas and certain lymphomas and myelomas. And while obesity rates have stabilized, they remain high, with more than two thirds of adults considered overweight or obese. That rate may not change for a while, given the fact that in 2013, 30% of adults said they had no recreational physical activity at all. “I was surprised to see how low the percent of adults who reach the recommended physical activity levels was,” says Fedewa. Government guidelines suggest at least 150 minutes of moderate activity each week, and only about half of adults accomplish this.

Screening is another area with both good news and bad news. Public health messages about the importance of getting mammograms to detect breast cancer, and colonoscopy to pick up colorectal cancer, have raised awareness about these diseases. But rates of colon cancer screening have remained around 58%. Part of the reason may have to do with cost; studies showed that uninsured people tend to have the lowest rates of cancer screening, something that the Affordable Care Act should change. It’s also possible that conflicting news about the benefits and risks of screening, and changing advice about who should be screened and when — in 2009 groups said that women between ages 40 and 40 years no longer needed annual mammograms — may also hamper compliance.

More studies are also throwing out clues about the best anti-cancer diet, with fruits and vegetables at the top of the list. But, says Fedewa, “only 15% of adults ate the recommended three or more servings of vegetables a day. That’s surprising, and pretty low given all the messages about eating healthier.”

Also discouraging is the continued use of tanning beds despite the fact that the International Agency for Research on Cancer lists the devices as cancer-causing to people. In 2014, 4.4% of adults, and 20% of high school girls, reported using the beds in the previous year. That may explain why rates of melanoma, unlike some other cancers, have been increasing in the past 30 years.

“I don’t think there is one message” about how we’re doing in preventing cancer, says Fedewa. “It’s not all doom and gloom. There is a lot to be appreciated for what we’ve done in tobacco control; that’s a great public health accomplishment. But there is room to grow.”

TIME medicine

How 3D Imaging Can Tell Exactly How Old You Are

You may be able to dodge questions about your age, but your face can’t

For the first time, scientists have used 3D imaging of a people’s faces to predict their age. The 3D information was so accurate, in fact, that it was better at pinpointing age than the best known marker, a test that involves studying the DNA.

Reporting in the journal Cell Research, Jing-Dong J Han, from the Chinese Academy of Sciences-Max Planck Partner Institute for Computational Biology, found that certain facial measures are reliable predictor’s of a person’s biological age. The researchers analyzed 3D facial images from more than 300 people, and matched them up with measurements from several dozen blood markers including cholesterol and albumin. Specifically, the width of the mouth and nose, and the distance between the mouth and nose tend to expand with age, and the eyes tend to droop over time. Measuring this change provides a relatively stable way of tracking, and predicting, a person’s age.

“Overall facial features show higher correlations with age than the 42 blood markers that are profiles in routine physical exams,” says Han.

 

Weiyang Chen–2015 Nature Publishing Group. Visualizations of facial aging.

MORE: Human Faces Can Express at Least 21 Distinct Emotions

She arrived at the finding after hearing a colleague present work on using 3D facial images to quantify racial differences. “It immediately struck me that facial images might be a potential good phenotype to include in our study to quantify the extent of aging,” she says. “I did not expect to see such remarkable changes with age, nor did I expect the 3D images to be such an accurate biomarker for biological age.”

Why is it important? Han says that pinpointing how quickly a person is aging via the relatively easy 3D algorithm could have useful health implications that go beyond keeping people honest about their age. Such a measure might provide a window into deeper physiological processes that could be aging abnormally fast. “It might have important implications for assessing the risks of aging-associated diseases, and for designing personalized treatment schemes to improve their life styles and health,” she says.

TIME Exercise/Fitness

This Study Busts Your Work Out Excuse

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Brent Winebrenner—Getty Images/Lonely Planet Images

Air quality may not be the best in cities, but the benefits of physical activity can outweigh the harms of breathing in pollutants

Exercising outdoors is certainly preferable to being cooped up in a stuffy gym, but if you live in an urban area, the pollution from cars and buses may give you pause. It shouldn’t. Zorana Andersen from the center for epidemiology and screening at the University of Copenhagen and her colleagues report in the journal Environmental Health Perspectives that being active trumps some of the negative health effects that breathing in polluted air might have.

MORE: Pollution: Dangerous to Joggers

In a study involving 52,061 people who were followed for around 13 years, Andersen found that those who were more active were less likely to die during the study than those who were more sedentary, regardless of the pollutant levels where they lived. The researchers asked the participants to detail their physical activities, including their leisure sports, how much they walked, whether they biked or walked to work, and whether they spent time gardening. They compared these responses to the levels of nitrogen dioxide near their homes; NO2 is a gas produced from the burning of fossil fuels in cars, and is an ingredient for other harmful pollutants such as ozone and particulate matter, which can cause respiratory illnesses. Previous studies found that walking along a busy London street, for example, caused a drop in lung function and that cycling or running near high traffic roadways also compromised people’s respiratory functions slightly.

In Andersen’s study, however, people who participated in sports showed a 22% lower risk of dying from any cause during the 13-year followup, while those who cycled regularly showed a 17% lower risk and people who spent time gardening showed a 16% lower risk compared to those who didn’t do either of those activities — and regardless of the pollution levels where they lived.

MORE: Ozone Can Harm the Heart in as Little as Two Hours

“We found an even more positive message around physical activity than we even hoped for,” says Andersen. “Physiologically it’s plausible that you inhale more particles [of pollution] when you exercise in polluted areas, and we thought maybe the accumulated lifetime effect of this would reduce the benefit of exercise. But we don’t see that.”

Essentially, the benefits of being active were strong enough to overcome some of the negative effects of breathing in pollutants. That makes sense, she says, because even if people aren’t exercising to avoid inhaling pollutants, they are still exposed to them, and Andersen’s study shows that even if exercises might be exposed to slightly higher levels of compounds like NO2, that still doesn’t negate the positive effects of physical activity on their heart, blood sugar levels and more. In fact, for specific conditions, the benefits of exercising remained quite high; active people even in highly polluted areas had a 66% lower chance of dying early from diabetes compared to those who didn’t exercise.

She notes, however, that some cities may have significantly higher pollution levels than Copenhagen, where the participants lived, and it’s not clear yet how greater concentrations can affect the exercise-pollution-mortality balance. So if you have a choice for working out, biking or walking in a less polluted area, however, such as a park or a quieter side street, that might be a good idea. But don’t worry too much if you don’t. “Being active prolongs life more than staying away from air pollution,” says Andersen. “So pollution shouldn’t be a barrier to exercise.”

TIME medicine

Who Should—And Who Shouldn’t—Take Vitamin D

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Here's what experts say, based on the latest evidence

Does your diet need a little extra D? For researchers, it’s one of nutrition’s most vexing questions. “It’s the wild, wild west,” says Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School. “The issue has become murkier over time rather than clearer.” Research is mixed about whether doctors should routinely test for vitamin D levels, like they do for cholesterol, and whether people should be supplementing their diets with vitamin D pills.

Case in point: a study just released in JAMA Internal Medicine showed that vitamin D did not lower the risk of falls among an elderly population in Finland. The study, which compared the effects of exercise against vitamin D supplements on falls and resulting injuries, did find, however, that exercise cut the chances of more severe injury from falls in half compared to those who didn’t exercise.

MORE Want to Stay Healthy? Don’t Rely on Vitamins

But that doesn’t mean that vitamin D isn’t worth taking at all. The Institute of Medicine (IOM), and the U.S. Preventive Services Task Force (USPSTF) both recently reviewed all of the evidence on vitamin D and its health effects and concluded that in many cases, D supplementation is beneficial—with some important caveats. The two groups say that 600 international units (IU) are generally enough for most healthy adults and that higher doses of vitamin D don’t necessarily produce more health benefits. They also stress that those benefits are limited to bone health; there isn’t enough evidence to support the idea that taking the vitamin can protect against heart disease, cancer, diabetes or cognitive decline, all benefits suggested by some smaller studies.

“More isn’t necessarily better,” says Manson, who served on the IOM committee. “In some cases, it can be worse.”

Overdoing vitamin D can lead to calcium in the urine, which can cause kidney stones. Extremely high doses—around 10,000 IU a day—can trigger calcium deposits in the blood vessels, which can lead to clots that cause heart attacks. The IOM panel recommended no more than 4,000 IU of vitamin D daily to avoid these potential problems.

MORE Want to Build Endurance? Cut Back on Vitamin C and E Supplements

When people are tested for vitamin D deficiency and come up short, some researchers caution against treatment. In addition to the dosage risks, there’s also evidence that the lab tests for the type of vitamin D circulating in the blood, 25-hydroxyvitamin D, may not be the most reliable measure of a person’s D levels. Plus, not all labs use the same standard test for picking up 25 hydroxy D, and they set different standards for what are considered normal levels. “Clinicians are often left chasing a number, and trying to get patients’ blood levels up to a certain point,” says Manson. “But when you think about how many people are screened for vitamin D, and the concerns about the reliability in how it’s measured, and the differences in what is considered normal ranges across laboratories, it’s really concerning.”

Better data may be coming soon, however. Several large trials are underway in which people are randomly assigned to take different levels of vitamin D supplements so researchers can study their health outcomes, from bone problems to heart disease, cancer, diabetes and more. Manson is overseeing the largest of these, called VITAL, which has 26,000 participants. The results from these studies, which are being conducted in the U.S., Europe, Australia and New Zealand, should be available in 2017. “We should have conclusive answers in about three years,” Manson says.

The studies will also look specifically at whether vitamin D levels and metabolism differ across racial and ethnic groups. Some studies have hinted that disparities by race in heart disease and certain cancer risks may be due to vitamin D, and the randomized trials will hopefully provide more information on whether that’s true.

In the meantime, Manson says doctors and patients should follow the IOM and USPSTF guidelines: doctors should not order vitamin D blood tests for all of their patients, and people shouldn’t take more than 600 IU of the vitamin if they are otherwise healthy. The only people who may need regular testing for vitamin D deficiency, and possible supplementation, are those with malabsorption problems like Celiac disease, those who have had bypass surgery, or people who have already had fractures and have been diagnosed with osteoporosis. People taking certain medications, including treatment for tuberculosis, may also need to consider vitamin D pills.

For everyone else, however, universal screening isn’t necessary—and there isn’t any reason to take more than the recommended daily allowance of vitamin D.

Read next: The 4 Most Confusing Things About Sugar

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TIME Depression

How Pilots Are Screened for Depression and Suicide

While it’s not clear exactly why Germanwings Flight 9525 crashed into a French mountainside, the black box from the cockpit raises questions about whether mental health issues were involved, and how aviation officials identify and monitor the mental health of pilots.

Prosecutor Brice Robin said that the cockpit recordings suggest the lead pilot was locked out of the flight deck after leaving for the restroom, and that co-pilot Andreas Lubitz “voluntarily allowed the aircraft to lose altitude. He had no reason to do this. He had no reason to stop the captain coming back into the cockpit.” As investigators search for a second black box, experts are trying to piece together the reasons why Lubitz acted the way he did. His mental state remains a possible cause.

If the investigation reveals that mental health played a role, it wouldn’t be without precedent. In a 2014 study in the journal Aviation, Space and Environmental Medicine, researchers looked at 20 years of data for what they called “aircraft assisted suicide.” From 1993-2012, 24 of 7,244 plane crashes were thought to be deliberately caused by a pilot. That’s less than 1% of the total, but it’s still enough to raise questions about the mental health stressors of pilots.

“I really wish that we had some kind of deeper thinking about this issue, because it’s one of the most difficult in aviation medicine,” says Alpo Vuorio, MD, PhD, the study author and an aviation specialist in occupational medicine at the Mehiläinen Airport Health Centre in Finland. He screens pilots and cabin crew of commercial airlines for health issues—including mental health issues—and says he sees any given commercial pilot once a year for a short visit.

Commercial pilots have to pass a physical and mental evaluation every six months (for those over 40) or once a year (for those under 40) in order to be certified to fly a passenger plane. The emphasis, however, is on the physical and less on the mental, mainly because mental health is harder to quantify.

“You somehow try to see if the pilot is well, and it’s not the easiest thing,” Vuorio says. Pilots answer yes-or-no questions about their mental health, Vuorio says, like if they’ve ever tried to attempt suicide or visited a psychiatrist. “You speak yes or no, but it’s up to you, what you tell,” he says. Pilots can visit several different locations for these examinations, he says, and if they don’t occur in house, past data don’t appear on the screen.

And pilots aren’t likely to divulge any potential mental health problems, including signs of depression or anxiety, because that would take them out of the sky. “Pilots aren’t going to tell you anything, any more than a medical doctor would about their mental health,” says Scott Shappell, professor of the Human Factors Department at Embry-Riddle Aeronautics University who is a former pilot and crash scene investigator.

Pilots, like doctors and policemen and others with high-stress jobs, tend to be good at compartmentalizing — walling off difficult or emotional experiences so they don’t interfere with their ability to function day-to-day. Medical examiners who evaluate pilots for their recertification also aren’t always trained in mental health, so they may not recognize subtle signs of conditions such as depression or alcoholism.

According to Dr. William Sledge, medical director of the Yale-New Haven Psychiatric Hospital who has evaluated pilots for the Federal Aviation Administration, about 40% of pilots he saw were for alcohol related problems, and a third for depression or anxiety. Only about half of the latter group reported their problems themselves, however. The other half were referred to Sledge only after incidents required their superiors to intervene.

“The problem is there is no incentive” to report mental health issues, says Shappell. “They know that if they self report, the way the system is designed, it will be a black mark.”

In a statement, the FAA said: “Pilots must disclose all existing physical and psychological conditions and medications or face significant fines of up to $250,000 if they are found to have falsified information.”

In the case of mental health evaluations, pilots are taken off the flight schedule while they are treated or begin antidepressant medications. Until 2010, even these drugs were banned, and pilots required them could no longer fly.

When the U.S. Air Force began requiring annual suicide prevention and awareness training in 1995, including screening for mental illness, the suicide rate plummeted from about 16 suicides per 100,000 members to about 9.

Even for experts, however, judging whether a pilot is suicidal is one of the hardest parts of the job. That’s no surprise, since the struggles of spotting and talking about suicide plague our entire society, says Barbara Van Dahlen, a licensed clinical psychologist and the founder and president of Give an Hour, a network of volunteer therapists. “In our society we are so quick to try to make it ok, to say it will pass and to say suck it up,” she says. “We really don’t listen to ourselves and we don’t listen to others very effectively.”

But pilots and others in high-pressure occupations face several unique stressors, she says, like having a physically demanding job and being responsible for other lives. “In a lot of positions of authority and leadership, those people are supposed to be capable and on top of things,” she says. “They don’t have a lot of people to share with and talk to, to be less than perfect and less than OK. That adds to the stress.”

One study of suicides among general aviation pilots—civilians who aren’t leading scheduled commercial flights—published in the journal Aviation, Space and Environmental Medicine, looked at 21-years’ worth of general aviation accidents as reported by the National Transportation Safety Board between 1983-2003. During that time, 37 pilots either committed or attempted suicide by aircraft, and nearly all resulted in a fatality. 38% of the pilots had psychiatric problems, 40% of the suicides or attempts were linked to legal troubles, and almost half, 46%, were linked to domestic and social problems. 24% of the cases involved alcohol and 14% involved illicit drugs.

Having ready access to a plane also seemed to be a contributing factor, too; 24% of the crashed planes in the study were used illicitly.

Read next: German Pilots Cast Doubt on Blaming of Co-Pilot for Crash

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