The year in health: 7 things experts told us to avoid

Being rich makes you more likely to lie, cheat, and steal. A series of experiments conducted on volunteers with annual incomes ranging between $16,000 and $150,000 found that the wealthiest were most likely to cheat to win a $50 prize, take candy from children, and pocket extra change given to them by mistake. Drivers of pricier cars were also four times more likely than those who drove cheaper models to cut off other drivers and pedestrians. Being wealthy seems to insulate you from the outside world and make you "less likely to perceive the impact" that your behavior has on others, says study author Paul Piff.

Sleeping in on the weekends can make you fat. A German study found that a person's odds of being overweight increase 33 percent for every hour of difference between their weekday and weekend sleep schedules. Two out of three people effectively commute between two time zones each week, disrupting their circadian rhythms. That "social jet lag" leads them "to eat at times when the body doesn't want to eat or isn't prepared for digesting food properly," thus leading to weight gain, says study author Till Roenneberg.

Too much exercise may hurt you more than it helps. While being a runner lowers your risk of early death by nearly 20 percent over not running, running more than 20 miles per week appears to cancel out that benefit. Jogging slowly decreases mortality risk, whereas running at a pace faster than 8 minutes a mile has been found to put extra stress on the heart. Studies have shown that more than an hour of intense aerobic activity per day can cause serious heart problems — including scarring, an irregular heartbeat, and clogged arteries. Many people wrongly assume that "if moderate exercise is good, then more is better," says study author James H. O'Keefe. But beyond an hour, "you reach a point of diminishing returns."

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Playing youth soccer can permanently damage your brain, as can other sports that involve repeated blows to the head. Mounting evidence shows that the routine hits young athletes take playing football, soccer, lacrosse, and even volleyball can cause cognitive problems. Girl soccer players have more concussions than any other young athletes except football players. "What's happening in this country is an epidemic of concussions," says sports physician Bob Cantu, who warns that brain injuries can affect some young people "for the rest of their lives."

Worrying about everyday problems will shorten your life. A British study found that people who reported feeling even mild anxiety — the sort that distracted them, depleted their self-confidence, or occasionally kept them awake at night — were 16 percent more likely to die over a 10-year period than people with no such concerns. About one in four people experiences mild anxiety, but most go untreated. Mild stressors — including those surrounding work, finances, and relationships — are so common that they're virtually impossible to avoid, but psychiatrist Glyn Lewis says exercise, meditation, or talk therapy can tame "their biological impact."

Breathing city air raises your risk of heart attack and stroke. After analyzing a decade's worth of data, researchers found that Boston residents were 34 percent more likely to have a stroke following a day of "moderate" as opposed to "good" air quality, under Environmental Protection Agency standards. In reality, "there is no safe level" of air pollution, says Johns Hopkins professor Roger Peng. Inhaling fine particles from car exhaust and power plants can damage the heart and lungs in much the same way cigarette smoke does: by clogging arteries, increasing inflammation, and raising heart rate and blood pressure.

Breathing indoor air isn't safe either. Exposure to carbon dioxide — even at levels considered in line with good ventilation — can make you dumber. Researchers tested the reasoning skills of volunteers while exposing them to different levels of CO2 and found that as levels increased, the volunteers' strategic and leadership abilities worsened to a degree "so astonishing that it was almost hard to believe," says epidemiologist Mark Mendell. Alarmingly, the highest levels of CO2 that he and colleagues measured, 2,500 parts per million, can easily be found in buildings — including schools — that are in perfect compliance with current ventilation codes.