Effects of exposure to morning bright light in the blind and sighted controls

Seven blind subjects and 11 sighted controls were exposed to 3300 lux of cool-white fluorescent light for either 1 h or 15 min in the morning for 2 weeks during the winter. Serum 25-hydroxyvitamin D3 concentration, melatonin concentration in saliva, body temperature from the armpit, subjective sleepiness, and depressive symptoms were measured before and after the 2-week trial. The intervention resulted in a significant elevation in the concentration of melatonin at 21.00 hours in the healthy controls but at 23:00 hours in the blind subjects. The body temperatures measured were increased in the controls but decreased in the blind in the morning following the cessation of the intervention, and these opposite changes resulted in significant differences in the temperatures between the two groups. The decreases in the body temperature were associated with the increases in the levels of melatonin in the blind but not in the controls. Bright light administered in the morning decreased subjective sleepiness and improved mood in the healthy controls and in the blind subjects as well. The intervention had no effect on the levels of vitamin D in either of the two groups.