Men worked harder to earn money for charity when someone was watching them, unless they had been given testosterone. In a University of Vienna study of 192 men, a single dose of the hormone wiped out that watched-by-others boost in generosity. Each man rubbed a gel onto his upper arms and shoulders. For half of them it held 150 milligrams of testosterone, and for the rest it was an identical gel with none, and neither the men nor the researchers knew who got which. The men then played a learning game, working out which symbols paid off, sometimes to win money for themselves and sometimes for a charity they picked. Neuropsychopharmacology published the study in 2023. Some men played while two women, introduced as charity representatives, sat in the room watching. The rest played alone. They were told nobody would ever see their results. Men on the plain gel made more correct choices for the charity when they were being watched. Men on testosterone chose the same way whether anyone was watching or not. The hormone left their ability to learn the game intact, and when they were watched, it changed how closely their choices followed what they had learned. Among men on the plain gel, those who cared most about conformity and tradition were the most consistent when watched. Testosterone erased that link. The authors describe the extra generosity in front of an audience as strategic, a way of looking good, and say testosterone pushed against that kind of conformity. This was one dose, a lab game, and healthy men aged 18 to 40. For these men, testosterone removed the extra effort that only appeared when someone was watching.

Losing just 1.36 percent of your body weight in water, about 800 milliliters for a 60 kg woman, left young women more tired and less focused. They also got more headaches, in a University of Connecticut study. Twenty-five women around age 23 spent three separate 8-hour days in the lab. On two of those days they became mildly dehydrated through moderate exercise, and on one of them they also took a water pill. On the third day they stayed properly hydrated. Throughout each day, they answered mood questions and took thinking tests, both at rest and while exercising. The study was published in the Journal of Nutrition in 2012. At just 1.36 percent dehydration, the women felt less energetic, more tired, and worse overall on a standard mood questionnaire. They also said tasks felt harder, found it harder to concentrate, and reported more headaches. These effects showed up both at rest and during exercise, yet most scores on the thinking tests held steady, so the damage showed up in how the women felt far more than in how they performed. Part of the dehydration came from exercise and a water pill, a different route from simply forgetting to drink at your desk, and 25 women is a small group. In this study, a shortfall of less than a liter of water was enough to make ordinary tasks feel harder.

People who ate breakfast once a week or less had nearly three times the odds of developing depression symptoms over three years, compared with people who ate it every day. A study of 716 workers in Japan found the risk climbed as breakfast got rarer. At a Japanese electrical manufacturer, 716 employees aged 19 to 68 answered detailed questions about what and how often they ate. None of them had depression symptoms or a mental health diagnosis at the start. Three years later, researchers from Japan's National Center for Global Health and Medicine checked who had developed symptoms using a standard depression questionnaire. The study appeared in Psychiatry Research in 2019. Breakfast frequency was sorted into five groups: daily, 5 to 6 times a week, 3 to 4 times, 1 to 2 times, and once a week or less. People in the rarest group had 2.9 times the odds of developing depression symptoms, even after accounting for the rest of their diet and their lifestyle. The odds tended to rise with each step down in breakfast frequency. Low mood can make people skip meals, which raises a chicken-and-egg question. Starting with people who had no depression symptoms helps with that, although it can't settle it completely, and every participant worked for the same company in one country. Among these 716 employees, the ones who almost never ate breakfast were the likeliest to develop depression symptoms three years later.

Optimists work harder and plan to keep working longer, according to Duke University finance professors Manju Puri and David Robinson. The most extreme optimists went the other way: they worked fewer hours and saved less money. Each person's guess about how long they would live became the optimism score. Puri and Robinson took answers from the Federal Reserve's Survey of Consumer Finances and compared them with official life expectancy tables, so people who expected to outlive the statistics counted as optimists. The score lined up with standard psychology tests of optimism and with people's hopes for the economy. The study appeared in the Journal of Financial Economics in 2007. Optimists worked more hours each week and expected to retire later. They saved more, put more money into individual stocks, and were more likely to remarry after a divorce. Self-employed people scored as more optimistic than regular employees. Extreme optimists, the people who expected to live far longer than the tables predicted, looked different. They worked fewer hours, saved less, were less likely to pay off their credit cards regularly, and were more likely to smoke. Survey data like this can't show which comes first, since hard work and savings might also make people feel more hopeful. Across American households, a moderate overestimate of your future went with working harder and planning ahead, and a wildly inflated one went with the opposite.

Eating 85 percent dark chocolate every day for three weeks lowered negative moods in a randomized trial, and the people who ate it ended up with more varied gut bacteria. The 70 percent chocolate had no clear effect on mood. Seoul National University researchers split 48 healthy adults aged 20 to 30 into three groups. One group ate 30 grams a day of 85 percent dark chocolate, about a third of a standard 100-gram bar. Another ate 30 grams of 70 percent chocolate, and the third ate none. The study appeared in the Journal of Nutritional Biochemistry. Mood was tracked with a standard questionnaire that measures good and bad feelings, such as feeling upset, nervous, or irritable. After three weeks, bad feelings dropped in the 85 percent group, and the 70 percent group showed no clear change. Stool samples from the 85 percent group showed a wider variety of gut bacteria than the no-chocolate group. One type, Blautia obeum, went up, and another, Faecalibacterium prausnitzii, went down. People whose gut bacteria became more varied, and whose Blautia obeum rose the most, had the biggest drops in bad mood. Dark chocolate may work like food for certain gut bacteria, the researchers suggest, and those bacteria could affect mood through the connection between the gut and the brain. Each group had only 14 to 18 people, and the link between bacteria and mood is a correlation. In this trial, the darker chocolate lowered bad moods within three weeks, and the milder one left mood about where it started.

Thirteen women living with a partner who has ADHD said so much of daily life fell on them that Hebrew University researchers concluded they should be recognized as caregivers. The study's title quotes the feeling: "I wish it wasn't all on me." Dana Zeides Taubin and Adina Maeir, occupational therapy researchers in Jerusalem, held long, open-ended interviews with 13 women who don't have ADHD themselves. Each was in a relationship with a partner diagnosed with adult ADHD. The study appeared in the journal Disability and Rehabilitation. Three themes came up across the interviews: how ADHD shows up in everyday life, the burden that falls on the partner, and the ways women learned to cope. Their accounts showed their partners' symptoms placing a heavy weight on them. Learning about ADHD, setting limits, and building ways to work around ADHD-related barriers as a team were the main strategies the women developed. Many of them took on a caregiving role inside the relationship. Doctors treating adults with ADHD should see the whole household, the researchers argue, and offer both partners education and counseling. They also suggest peer support groups, individual counseling, or couples therapy built around life with ADHD. All 13 women were white and in heterosexual relationships, a limit the authors point out themselves, so the findings may look different in other couples. For these women, the organizing, remembering, and managing landed mostly on one side of the relationship.

Owning a dog was linked to 40 percent lower odds of developing disabling dementia over four years, in a study of 11,194 older adults in Tokyo. Cat owners showed no difference at all. Residents of Ota City, Tokyo, aged 65 to 84, filled out a detailed health survey in 2016. Researchers from the Tokyo Metropolitan Institute of Gerontology then followed them for about four years using Japan's long-term care records, where doctors rate whether someone's dementia is severe enough to need care. The study appeared in Preventive Medicine Reports in 2023. Only 8.6 percent of these older adults owned a dog. Dog owners can differ from everyone else in health, income, and lifestyle, so the team statistically balanced the groups on physical, social, and psychological traits before comparing them. Current dog owners had 40 percent lower odds of disabling dementia than people who had never owned a dog or no longer did. Cat owners matched non-owners. Dog owners who also exercised regularly had 63 percent lower odds compared with non-owners who didn't exercise, and dog owners who weren't socially isolated had 59 percent lower odds than isolated non-owners. Walking a dog counts as moderate exercise, and the researchers point to both the physical activity and the social contact that come with daily dog care. Cats rarely need a walk around the neighborhood. Healthier people may also be more able to keep a dog, and a study like this can't fully separate the two. Across 11,194 older adults, the lowest dementia risk showed up in dog owners who were also active and socially connected.

Leaving messages on read is tied to feeling overwhelmed. A study in Computers in Human Behavior found that too many messages, heavy workloads, and time pressure made people anxious and more likely to put off replying, and messages that looked useful got answered faster. Researchers from Sun Yat-sen University, Wuhan Institute of Technology, and Yunnan University started with in-depth interviews about how people handle messaging apps. From those conversations they built a model of why replies get delayed, then tested it with survey data from app users in China. The study was published in 2023. Forgetting to deal with messages, putting off replies, and reading without answering came up again and again in the interviews. The researchers call these negative use behaviors, small ways people push back against a flood of information. Too many messages, too much work, and tight deadlines all raised two feelings: anxiety about keeping up, and a mental resistance to the app itself. Both feelings went with paying less attention to messages and replying later. Messages that looked worth reading interrupted that chain, because when usefulness was high, the path from feeling overloaded to replying late got weaker. People still felt the overload, but useful messages were more likely to get an answer. All the data came from one country at one point in time, so the authors want studies in other countries and over longer periods. In this study, the messages that got faster replies were the ones people saw as useful.

People with tattoos bigger than the palm of their hand had more than double the risk of skin cancer and lymphoma, a cancer of the immune system, in a Danish twin study. The lymphoma number that went viral rests on 32 cancer cases, and only 7 of them had tattoos. Researchers at the University of Southern Denmark used the Danish Twin Registry for two studies. One followed 2,367 randomly chosen twins. The other looked at 316 twins born between 1960 and 1996, from pairs where at least one twin got cancer. Cancer diagnoses came from national records, tattoo details came from a 2021 survey, and BMC Public Health published the results in 2025. Ink from a tattoo travels from the skin into the blood and builds up in nearby lymph nodes, the small immune filters in places like your armpits and neck. The researchers worry the ink causes long-lasting inflammation there. Over years, that could push cells to grow out of control. Tattooed people in the second study had a 62 percent higher risk of skin cancer. For tattoos larger than a palm, skin cancer risk was 2.4 times higher and lymphoma risk was 2.7 times higher. In the group of 2,367 twins, tattooed people had about 4 times the risk of skin cancer. Once tattoo size was ignored, tattoos showed no clear link to lymphoma. Comparing each tattooed twin with their own untattooed sibling, the strongest test a twin study can run, wasn't possible for lymphoma because there were too few pairs. For skin cancer, that twin-versus-twin test used just 14 pairs and found a much smaller link that could easily be chance. Sun exposure wasn't measured either, and the authors note that tattoos can make skin cancers harder to spot. The concern about ink is serious enough to study further. The headline lymphoma risk, though, comes from 7 tattooed patients.

Living simply is linked to greater happiness. A review of 259 groups of people found that the more someone cares about money and possessions, the lower their well-being, and the worst effects show up in how people see themselves and in risky behavior. Helga Dittmar and colleagues at the University of Sussex combined 753 results from studies around the world. Their review was published in the Journal of Personality and Social Psychology in 2014. People who see possessions as a sign of success and a path to happiness showed the strongest link to lower well-being, and people who simply care about money showed a weaker one. Risky health habits, compulsive shopping, and feeling bad about yourself had the biggest links. Life satisfaction and bad moods showed smaller links that still held. Jobs and schools that reward materialistic values made the link stronger, and it also shifted with a country's economic growth and the gap between rich and poor. Unmet basic needs were the best explanation for the pattern: feeling capable, feeling free to make your own choices, and feeling close to others. A life built around stuff may crowd those out. Most of the studies took one snapshot in time, so the direction isn't proven, and the effects were modest. Across 259 groups, the people doing best were the ones who felt capable, free, and close to other people.

Regular walking for a year grew the memory center of older adults' brains by 2 percent, undoing one to two years of age-related shrinkage. A study of 120 older adults showed the brain can still grow late in life. Memories form in the hippocampus, a seahorse-shaped part of the brain that shrinks with age and raises the risk of dementia as it does. Kirk Erickson and colleagues at the University of Pittsburgh and the University of Illinois randomly split 120 older adults into two groups: one did walking workouts, and the other did stretching and toning. The study appeared in PNAS in 2011. In the walking group, the front part of the hippocampus grew by 2 percent. In the stretching group, it shrank, as normally happens with age. The walkers also got better at remembering where things are. Their bigger hippocampus came with higher levels of BDNF, a protein that works like fertilizer for brain cells. People who were fitter at the start lost less brain volume, even in the stretching group. Other brain areas the team checked stayed the same. Brain scans measure size and can't count new brain cells, so the study can't say how many were added. Even so, the memory center grew late in life, and a year of regular walking was enough to reverse its shrinkage.

Mental health is physical health. A study of 5.9 million people in Denmark found that people diagnosed with a mental illness were more likely to later develop physical diseases, in 76 of the 90 combinations researchers checked. Researchers at Aarhus University used Denmark's national health records for everyone born in the country between 1900 and 2015, and followed them from 2000 to 2016. About 1 in 9 people, nearly 700,000, were diagnosed with a mental disorder. The study was published in the New England Journal of Medicine in 2020. Ten types of mental illness were compared with 9 types of physical disease, such as heart disease, cancer, and lung problems. In 76 of the 90 pairs, people with the mental illness were more likely to develop the physical disease afterward. The typical increase was 37 percent. Eating disorders showed the biggest jump, with about 3.6 times the risk of urinary and reproductive organ problems. Within 15 years of a diagnosis, the risk of a physical disease ranged from under 1 percent for one pairing to 54 percent for heart and blood vessel disease among people with brain-based disorders such as dementia. A few pairs showed lower risk, like schizophrenia and bone and muscle problems. Medication side effects, habits like smoking, fewer doctor visits, and shared biology could all play a part, and the study can't separate them. Across nearly 6 million people, a mental health diagnosis came with higher physical health risk in 76 out of 90 comparisons.

Winning a lottery to buy a Nintendo Switch or PlayStation 5 made people measurably happier. During pandemic shortages, stores in Japan used lotteries to decide who got a console, and researchers used that luck of the draw to study 97,602 people. Most research on gaming and mental health just compares gamers with non-gamers, which can't show what causes what. Between 2020 and 2022, consoles were so hard to find in Japan that stores held lotteries, and winning or losing came down to pure chance. Of the people surveyed, 1,773 had entered a Switch lottery and 6,419 a PS5 lottery. The study appeared in Nature Human Behaviour in 2024. Owning a console lowered emotional distress and made people more satisfied with life, with effects ranging from small to moderate. People whose gaming time went up the most after winning improved the most. One console gave smaller benefits to teenagers and women, while the other gave bigger benefits to teenagers. Past three hours of gaming a day, the benefits got smaller. The study also happened during the pandemic, when people were stuck at home, so the effect might be smaller in normal times. For this group, a console won by lottery made people happier, and the gains leveled off after about three hours of play a day.

Happiness is linked to later success. Stop treating happiness like a reward you earn after the win. A review of 225 studies found that happy people tend to become more successful at work, in relationships, and in health, and that happiness often comes first. Psychologists Sonja Lyubomirsky, Laura King, and Ed Diener pulled the research together in Psychological Bulletin in 2005, testing the reverse of the usual assumption that success makes you happy. Their question was whether feeling good often helps you succeed. Snapshot studies showed happy people doing better in marriage, friendships, income, work, and health. Studies that followed people over years showed happiness came before many of those wins. And lab experiments, where researchers put people in a good mood on purpose, showed good moods made people more social, more helpful, and more creative. How often people feel good mattered most to the researchers, which is why "frequent" is in the paper's title. Small, regular good moods were the pattern connected with success. Some effects were modest, and studies measured happiness in lots of different ways. All three kinds of evidence still pointed the same way. Happiness showed up before success often enough that waiting to be happy until after you succeed gets the order backward.

This is a really interesting way to think about ADHD. A substantial subgroup of people with ADHD appear to have a delayed circadian rhythm, with later melatonin onset and delayed sleep timing. The 2025 paper by Luu and Fabiano pulls together evidence that shifting the body clock earlier with things like morning light, consistent wake times and in some cases melatonin may improve ADHD symptoms, although much of the intervention evidence is still early.

Kids who played more video games gained more IQ points over two years, even after scientists accounted for their genes and family background. A study of 9,855 American children found gamers gained about 2.5 extra points. Researchers from Karolinska Institutet in Sweden and Vrije Universiteit Amsterdam used data from the ABCD Study, a large US project tracking how kids' brains develop. They tested intelligence at ages 9 to 10 and again two years later, and asked how much time kids spent watching videos, chatting online, and gaming. Smarter kids might pick different screen habits, so the team used DNA to account for each child's inherited tendency toward intelligence, along with family income and background. The study appeared in Scientific Reports in 2022. At the start, kids who watched more videos or chatted online more scored slightly lower, while gaming made no difference. Two years later, kids who gamed more than average had gained about 2.5 extra IQ points. Watching videos also seemed to help, by about 1.8 points, but that result went away when the researchers used parents' education in place of family income. Chatting online had no effect. Which games helped, and how much gaming is too much, the study can't say, and it looked at test scores with no data on school grades. Across nearly 10,000 kids, gaming still came with the biggest gain of any screen activity.

Sunlight may be the most underrated antidepressant. A study in The Lancet measured serotonin coming straight out of the brain in 101 men, and the brain made more of it on days with more bright sunshine. Many common antidepressants work by boosting serotonin, a brain chemical that affects mood. Measuring how much the brain makes is hard, so researchers at the Baker Heart Research Institute in Melbourne took blood from the neck veins that carry blood away from the brain. The study was published in 2002. Serotonin activity in the brain hit its lowest point in winter, and how fast the brain made it matched how many hours of bright sunshine there had been that day. Production climbed quickly as the light got brighter. Mood tends to dip in the darker months, and this finding fits that pattern. Seasonal affective disorder, a kind of depression that comes back every winter, follows the same calendar, and bright light therapy is already a proven treatment for it. Only healthy men took part, and the study measured a brain chemical with no mood measurement. The link was moderate, and people with clinical depression still need proper treatment. On the days with the most bright sunshine, the brains in this study made serotonin fastest.

Exercising before something stressful makes your body react less to the stress. In a Berlin study, young men who exercised for 30 minutes released less of the stress hormone cortisol during a tough test 90 minutes later. One group of men did 30 minutes of moderate exercise on a treadmill, and the other did 30 minutes of very light movement, with fit and inactive men assigned at random. An hour and a half later, each man lay in a brain scanner and did mental math under time pressure, with feedback designed to make him feel like he was failing. The study appeared in the journal Psychoneuroendocrinology in 2015. The men who exercised had a smaller cortisol spike during the test. Exercise raises cortisol for a while, and the body seems to respond by turning its stress system down, like a built-in brake. The men whose stress hormones rose the most during exercise had the smallest spike during the test. Brain scans showed more activity in the exercisers' hippocampus, a memory center, and less at the front of the brain, two areas that help control stress hormones. Fitter men also had smaller cortisol spikes in general. Only young men took part, so women and older adults might respond differently. About 30 minutes of moderate exercise, an hour and a half before a presentation, exam, or hard conversation, was enough to shrink the stress response in this group.

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