Here's a reason to set that alarm a little earlier: Being exposed to sunlight early in the morning (instead of later in the day) is associated with a lower BMI, a new Northwestern University School of Medicine study reports. This association was found regardless of other factors like how many calories people ate or how much they exercised.

Early morning light exposure accounted for 20 percent of the variation in BMI among people studied. Light sends an extremely strong signal to your body and brain to wake up and also helps regulate your body's circadian clock, says Kathryn Reid, Ph.D., one of the study's authors. Your circadian rhythm may impact your metabolism too. Reid points out that studies show that animals with changes to their circadian rhythm gain weight even though they didn't eat more. Messing with your body clock, then, and missing out on early rays may "alter the way your body processes the foods you eat, leading to weight gain," she says. What's more, it may also affect your hunger and satiety signals.