Light Therapy part 3

Overview of Light Therapy


Seasonal Affective Disorder & Gender

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, more 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.
Seasonal Affective Disorder & Age
Epidemiological studies report that the lifetime prevalence of SAD increases with age until the sixth decade. After the age of 50-54 the prevalence declines dramatically, such that the prevalence of SAD over 65 is very low. Nonetheless, patients over 65 may still present to clinics for treatment and clinical experience suggests their response to treatment does not differ from that of younger patients with SAD.
Other Considerations
The recall of lifetime episodes of seasonal depression is affected by the time of year the interview takes place; that is, patients interviewed during autumn or winter are more likely to report lifetime seasonal difficulties as compared to patients interviewed in the summer (Lam & Levitt, 1999). A study carried out in the UK showed a prevalence rate of SAD was calculated to be 2.4% according to the strictest DSM IV criteria (American Psychiatric Association, 1994). The majority of identified cases had not previously received a diagnosis of SAD from their general practitioner, although over half had been diagnosed with other forms of depression and had been prescribed antidepressant medication. Therefore although SAD was found to be common in the general population sample it appeared to be largely under-diagnosed and/or misdiagnosed (Michalak et al, 2001). One USA study, which used a structured diagnostic interview, reported that SAD patients were more educated than non-SAD patients, and that it was more common in rural settings. However, a Canadian study, which used a similar diagnostic interview, found no urban-rural or educational effects.


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