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All patients must meet the diagnostic criteria for recurrent major depression or bipolar mood disorder. Seasonal affective disorder (SAD) is then a sub-type specifier used to describe temporal variations of these disorders. As such, SAD is not considered a stand-alone diagnosis or comorbid condition to recurrent major depression or bipolar disorder. Common presentations include the initiation or worsening of depressive symptoms during the autumn or winter months, and full remission during the spring or summer months, or hypo-manic or manic symptoms presenting during spring or summer months.
Circadian and neurotransmitter factors are likely to contribute to the pathophysiology of SAD, although the exact mechanism of action remains ill-understood. The suprachiasmatic nucleus (SCN) of the hypothalamus is being increasingly recognised as the 'master regulator' of several systems implicated in seasonal mood regulation. Diminished light during the autumn and winter may cause a phase shift in various circadian rhythms, including sleep-wake cycle, body temperature, hormone levels, and melatonin secretion.
In a recent meta-analysis of 35 published studies ,the weighted CMR for AN was 5.1 deaths (95 % CI: 3.99-6.14) per 1000 person-years, translating into 5.1 % per decade or 0.51 % per year. One in five individuals with AN who died had committed suicide .The overall SMR was 5.86 (95 % CI: 4.17-8.26) with a mean follow-up period of 14 years. In a meta-analysis of SMRs in 2001, the overall SMR of AN in studies with 6–12 years of follow-up was 9.6 (95 % CI: 7.8-11.5) and in studies with 20–40 years of follow-up 3.7 (95 % CI: 2.8-4.7) . Age, case severity and study period influence mortality rates as well . In a Swedish study , a significantly higher mortality rate (4.4 % vs. 1.2 %) was found among female patients hospitalized due to AN in 1977–1981 compared with those hospitalized in 1987–1991.