by Wei Perng, PhD
Serotonin. Phototherapy may affect mood by stimulating serotonin, a neurotransmitter found in the gastrointestinal tract and central nervous system. Serotonin contributes to feelings of happiness and well-being, and levels are low in persons with depression or affective disorders. A deficit also may trigger cravings for high-carbohydrate, high-fat foods, which in turn will increase serotonin release via insulin secretion. By prompting serotonin release, phototherapy may ease these cravings and prevent excess consumption of unhealthy foods.
Melatonin. Phototherapy may stop inappropriate secretion of melatonin, which is released during darkness and causes sleepiness. Inappropriate melatonin released in response to long periods of daytime darkness results in daytime lethargy could also cause poor sleep quality. As we saw from a previous blog post by Chelsea Jenter, poor sleep is a risk factor for obesity. By helping to regulate sleep, light therapy may promote a healthier weight.
Glucose metabolism. Studies in rodents indicate that duration and timing of light exposure can actually affect weight gain, independently of caloric intake via glucose metabolism. Some evidence in humans also supports use of bright lights for weight loss. In a randomized trial, 34 overweight adult women - 10 of whom displayed SAD symptoms - were exposed to two different sessions: a 3-week session of morning phototherapy treatment and a 3-week session with a placebo light. What did the investigators find? As compared to the placebo, light therapy resulted in lower percentage body fat, fat mass, and appetite, with an average fat reduction of 0.35 kg. Interestingly, these differences were even more pronounced among participants with signs of SAD.
Does this mean that light therapy is the next best weapon to combat the obesity pandemic? It’s certainly not a miracle answer. But light therapy does seem to help people with seasonal affective disorder, and early results suggest some benefit for weight loss, though it requires more careful investigation. Furthermore, we need to know more about whether light therapy can cause side effects; some consumers report headaches and eye/skin conditions that are not inconsequential. For now, fighting the winter blues and a growing waistline is best countered by keeping up on exercise and eating well. But, turning on the light may help too.