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From SADwiki, the open SAD resource site for Seasonal Affective Disorder sufferers
Seasonal Affective Disorder afflicts both sexes, though virtually all studies of the prevalence of SAD report that women are more likely to suffer than males. The most widely reported statistic is that women are 3.5 times more likely to present symptoms of SAD. However such results may be confounded, for example, females might seek help more than males.
Academic studies have varied quite significantly in estimations of male to female ratio. Lee & Chan (1998) Pooled the epidemiological data reported in 40 studies on seasonal affective disorder to identify the male/female ratio. They concluded that about 70-80% of individuals with SAD are women. Among the 1,129 Ss (aged 28.7 - 47.0 yrs) recruited for these 40 studies, females out-numbered males 3.45 to 1.
More recent work by Lam & Levitt (1999) however argues that the average ratio across all studies is closer to 1.8 to 1. A sex difference in biochemical responses to climatic variables is postulated as one of the possible explanations of the observed females' increased vulnerability to seasonal affective disorder.
Partonen (1995) suggests that the mechanism may involve the action of the ovarian steroid hormones oestrogen and progesterone. Again, the reasons for differences in vulnerability by sex are unclear since the aetiology of the condition is poorly understood.