2017 Volume 29 Issue 2 Pages 143-151
The onset of bipolar disorder is influenced by the interaction of genetic and environmental factors. A previous study by the international research team found that a large increase in sunlight was associated with a lower age of onset. This study extends the analysis with more collection sites at diverse locations including locations in Japan. It also includes family history and polarity of first episode, and investigates whether the hours of daylight at the birth location affect the age of onset. Data from about 4000 patients with bipolar Ⅰdisorder were collected at 36 collection sites in 23 countries. Solar insolation values at the onset locations and the hours of daylight values at the birth location were obtained from the USA National Aeronautics and Space Administration (NASA) Surface Meteorology and Solar Energy (SSE) database. Generalized Estimating Equations (GEE) models were used to estimate the effect of solar insolation on the age of onset. There was a large, significant inverse relationship between maximum monthly increase in solar insolation and the age of onset. The effect was reduced by half if there was no family history and by one-third for initial episodes of mania than depression. More hours of daylight at the birth location during early life was associated with an older age of onset, suggesting reduced vulnerability to the future circadian challenge of the springtime increase in solar insolation at the onset location. Further research into the effects of the duration, intensity, timing and wavelength of sunlight is needed to better understand bipolar disorder.
