… and some of the things we were told to avoid

Daydreaming makes you unhappy. Harvard researchers randomly contacted volunteers throughout the day and had them describe what they were doing, what they were thinking about, and how they felt on a scale of zero to 100. People who were daydreaming often reported feeling sad or worried. When people’s minds wander, says study co-author Matthew Killingsworth, they tend “to wander toward negative thoughts,” regardless of the activity in progress. People who are intensely focused on what they are doing at that moment—especially sex—tend to report feeling much happier.

Lack of sleep will keep you fat. Two groups of study subjects were put on a reduced-calorie diet; one group was allowed to sleep just five hours a night and the other had a full night’s sleep. Both groups lost the same amount of weight, but the well-rested subjects lost twice as much of that weight in the form of fat. The sleep-deprived group lost more muscle mass and water, and woke up starving. “If your goal is to lose fat,” says University of Chicago researcher Plamen Penev, “skipping sleep is like poking sticks in your bicycle wheels.”

Sitting for prolonged periods shortens your life span. Epidemiologists found that people who sat for more than six hours a day were nearly 20 percent more likely to die over the 14-year study period than those who sat for less than three hours daily. Standing burns calories, boosts the ability of insulin to lower glucose, and activates an enzyme that sucks fat out of the bloodstream. “Sitting is hazardous,” says Marc Hamilton, a physiologist. “It’s dangerous.”

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Too much television hurts your kid in every possible way. Every hour of TV beyond average that younger toddlers watched made them, by fourth grade, 7 percent less engaged in class, 6 percent worse at math, and 10 percent more likely to be bullied; they also snacked more, exercised less, and had higher ratios of body fat.

Eating too much salt can subtract years from your life. Americans eat far more than the recommended amount of sodium, mostly in processed foods. Reducing the daily intake by three grams, or just half a teaspoon, would cut the number of heart attacks by 99,000—a 13 percent decline; strokes and new cases of heart disease would decline too, by 8 percent and 11 percent, respectively.

Cash receipts can be toxic. Forty percent of receipts from ATM machines, supermarkets, gas stations, and other major retail outlets carry significant traces of bisphenol A, or BPA, a chemical that has been linked to heart ailments, cancer, and behavioral and reproductive problems. Often found in plastics, BPA is also used as coating in the paper used to make receipts; it transfers easily to fingers and may penetrate the skin. Although the health risk is probably greater to cashiers than to shoppers, says researcher Frederick vom Saal, “I won’t touch receipts now.”

Running shoes can hurt your knees. An analysis of people running on a treadmill found that the use of running shoes led to 38 percent more torque, or twisting, around parts of the knee where osteoarthritis develops than barefoot runners experienced. In fact, the shoes put more strain on the knee than women’s high heels do. Unshod, a runner naturally runs on the balls of the feet, which allows the foot itself to absorb more of the impact. People who run on streets and hard pavement, of course, may not have the option of going barefoot, so for them researchers suggested a minimal running shoe with less padding.

Dogs and cats may be good companions, but they can break your leg. A new analysis of emergency-room data found that 86,000 people a year wind up in the hospital after tripping over a pet, its bowls, or its toys. Dogs cause nearly eight times more injuries than cats, mainly because they’re bigger and stronger, and can yank people down stairs or into holes when pulling on their leashes during walks.