Light might make you a lightweight—in a good way. It’s been known that bright light in the morning can reduce appetite and body weight. But that fact did not prove that light has a direct effect on weight. Early morning exposure to light could just be a marker for a regular sleep cycle, which is also associated with a healthy body weight.
The question was thus whether light exposure was associated with weight regardless of sleep patterns.
To find out, researchers had 54 adults record their diet and sleep for a week. The subjects also wore sensors that monitored the timing and intensity of their light exposure.
And independent of sleep habits, the participants' body weight corresponded to when they saw the light—even dim light, with just half the intensity of sunlight on a cloudy day. The study is in the journal PLoS ONE. [Kathryn J. Reid et al, Timing and Intensity of Light Correlate with Body Weight in Adults]
So early to bed and early to rise appears to indeed make you healthy. Jury's still out on whether it also makes you wealthy and wise.
[The above text is a transcript of this podcast.]