Supersensitivity to light: possible trait marker for manic-depressive illness.

Exposure to light during the night reduces plasma melatonin levels. A previous study showed that, in response to light, nighttime plasma melatonin levels fell twice as much in a group of acutely ill manic-depressive patients as in a group of normal subjects. The present study compares 11 euthymic manic-depressive patients not taking medications with 24 age- and sex-matched normal subjects. Melatonin levels in these patients also fell twice as much as the levels of the normal subjects, suggesting that supersensitivity to light may be a trait marker for bipolar affective disorder.