Just as getting the right amount of sleep helps you lose more fat, consistent exposure to light at night has the opposite effect, leading to extra pounds. Here's the interesting twist to this recent study: Living with more light at night triggered metabolic changes in mice despite no differences in the amount of food they ate or their activity levels.

In one experiment, researchers compared the biological attributes of mice exposed to a normal day-night cycle (16 hours of light, 8 of darkness), 24 hours of constant light and an unusual cycle of 16 hours of light and 8 hours of dim light, with free access to their food. The latter group of night-lighters gained 50 percent more weight (12 grams) than did the mice exposed to the average day-night cycle (8 grams). Also, the mice ate a majority of their food during the day, unusual for nocturnal creatures who eat far more at night.

A second experiment, restricting the food intake of mice exposed to varying amounts of light to times they would typically be active or resting, confirmed the earlier variation. Mice exposed to the dimmer light at night gained no more weight than the other groups so long as they were fed during times of normal activity.

Interestingly, these metabolic changes in mice may not entirely be brought on by variances in melatonin levels. Scientists believe exposure to dim light at night may also disrupt the expression of clock genes that control when animals feed and are active.

Perhaps, this recent report from an international consortium of health agencies listing shift work as one of 20 new causes of cancer really does deserve more of our attention.

Proceedings of the National Academy of Sciences October 11, 2010

EurekAlert October 11, 2010