SAD (seasonal affective disorder)
This depression is caused by the long nights experienced in high latitudes. Normal treatment is to make the sufferer extend the daylight hours with artificial lighting. Researchers have found that long nights cause a drop in the level of progesterone in the blood. One is tempted to speculate that SAD is not caused by the long nights but by the drop in progesterone. People have lived for centuries in high latitudes without suffering SAD, why now? Again it is tempting to draw a correlation between the incidence of SAD and the rise in environmental oestrogens.