Seasonal affective disorder (SAD) is a cyclical depressive disorder that typically recurs every year during the shorter days and longer nights of late fall-early winter. Much of the research on SAD has focused on changes in the photoperiod and the accompanying effects on circadian rhythms during winter. So it might come as a surprise that in Greenland, the suicide rate peaks during the summer months of continuous sun (especially at the highest latitudes). However, the rate of homicides and the sales of beer do not show the same seasonal variation (Björkstén et al., 2009).
Why might this be? Most suicides in Greenland are of the impulsive variety and are committed using violent methods. The authors' previous work observed the summer suicide spike (Björkstén et al., 2005), and now they wanted to determine whether homicides show the same seasonal pattern. They reviewed the evidence on serotonin, impulsivity, and violence, and hypothesized that altered serotonin turnover might be a common factor in both violent suicides and violent homicides (reasoning that increased serotonin turnover in spring and summer might enhance impulsiveness and aggression).
How was this assessed? Northern Greenland (obviously) shows the greatest seasonal extremes in the amount of light and darkness. The country maintains good statistics, and the Inuit population is considered to be relatively homogeneous. Thus, Björkstén, Kripke, and Bjerregaard (2009) examined computerized records listing the causes of all deaths in Greenland during the time period of 1968-2002. To determine whether alcohol consumption played a role in the rates of suicides and murders, the pattern of beer purchases at a major chain store from July 2005 to June 2006 were used as a proxy ("Detailed sales data are secret for business reasons").
The authors note some extremely tragic statistics:
The suicide rate in Greenland increased during the 1970’s from a historically very low level to one of the highest levels in the world, 107 per 100,000 person-years in 1990-1994. The increase has been most pronounced among teenagers and young adults. A rapidly increasing suicide rate has been reported from other areas going through radical changes like in Eastern Europe after the fall of communism and among aboriginal people confronted with modern lifestyle.We have previously demonstrated that the vast majority of suicides in West Greenland are violent and peak in the summer when the Northern half of Greenland has constant day-light and the Southern half has extremely long days. Depression has, however, been reported uncommon and the majority of suicides seem impulsive rather than depressive.The overall homicide rate in Greenland has been reported much higher than that of the other Nordic countries. Homicides are almost exclusively impulsive and committed under the influence of alcohol...Continuing in a depressing vein, there were 1351 suicides (80.5 % were men) and 308 homicides during the 35 year period under study.
Persons in upper teens and young adults were heavily over-represented among the suicide cases. Median age was 25 years...However, affective disorders could have been underdiagnosed in the population... we don't really know for sure. What we do know is that violent methods of suicide were used in 95% of all cases (n=1286), with men using violent methods 97% of the time and women 86% of the time (the latter percentage in stark contrast to the general population outside of Greenland). Figure 3a below shows the seasonal variation in all suicide cases. The annual peak occurred on June 11th and the trough in November-January, and the effect of seasonality was significant (p<0.001). For homicides (Fig. 3b), the calculated annual peak occurred on May 2nd, but the seasonal variation in homicides did not reach significance (p<0.10).
In 391 out of the 1351 cases (29%), the death certificate included a psychiatric diagnosis. In 214 cases (15.8%), there was a diagnosis of alcoholism or alcohol intoxication; two cases also had a diagnosis of psychosis. In only 52 cases (3.8%), there was a diagnosis of affective disorder, either unspecified or in the depressive state. In 104 cases, there was a diagnosis of psychosis. In addition to the 104 cases (7.7%), there were two with alcoholism and psychosis.
Figure 3 (Björkstén et al., 2009). Monthly distributions of suicides and homicides. The monthly distribution of all suicides (n=1351) is shown in Fig 3a and all homicides events (n=286) in Fig 3b. Please note that the scales on the Y-axes are different.
Finally, the seasonality effect for suicide was greater for those living above the Arctic Circle.
- Suicides were almost exclusively violent with significant summer peaks when there is either midnight sun or very long days. The suicides were more concentrated around the summer months at higher latitudes. At about 77ºN, 82% of the suicides occur during the period of constant day.
- In 29% of the suicide cases, there was a psychiatric diagnosis in the death certificate, however rarely depression (3.8%).
- Homicide deaths showed a non-significant increase in spring, and the rate was high compared to other Nordic countries.
- There was a bi-phasic seasonal variation for suicides related to alcohol, but no seasonal variation in consumption of beer.
- Light is only one of many factors in the complex tragedy of suicide, but this study shows that there is a possible relationship between light and suicide.
Björkstén KS, Bjerregaard P, Kripke DF. (2005). Suicides in the midnight sun--a study of seasonality in suicides in West Greenland. Psychiatry Res. 133:205-13.
Bjorksten, K., Kripke, D., & Bjerregaard, P. (2009). Accentuation of suicides but not homicides with rising latitudes of Greenland in the sunny months. BMC Psychiatry, 9 (1) DOI: 10.1186/1471-244X-9-20.
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