Opening up your windows in the morning may do more than just light up the house and wake you up. A recent study suggests that exposure to morning sunlight may help shrink waistlines, too.

Researchers at Northwestern University say the benefits of getting a little sunshine may extend to altering people’s metabolic function, appetite and body fat.

In a recent study, the researchers found that participants who got most of their light exposure earlier in the day were more likely to have a lower body mass index than people who were exposed to light later.

Researchers say what matters is not only how much light you receive, but also when you get it and for how long. They suggest that the most beneficial morning light is actually strong indoor light, rather than direct outdoor light, at least as it relates to influencing body mass index.

Other studies have shown similar findings. According to a separate study, when obese women reduced their body fat and appetite by simply getting 45 minutes of light between 6 and 9 a.m.

So why is there a link between light and body mass index? Researchers think it might be because light signals our internal body clocks … our circadian rhythms. Mornings are filled with “blue light,” which has a stronger influence on the circadian system.

This internal biological clock determines our periods of sleepiness and alertness throughout the day. It is influenced by elements such as sunlight exposure and temperature. Researchers say that when this rhythm is disrupted, sleeping and eating patterns are affected as well.

Blue light has also been linked to lowering stress. Researchers say morning short-wavelength blue light can wake up the body to be active, and thus, prepared for any daily activities.

So, soaking up that early morning sunshine may help you feel more awake and ready for the day.