Thursday, May 14, 2009

Suicide Rates in Greenland Are Highest During the Summer

by: crdagain

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...

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.
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).

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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At May 14, 2009 7:34 PM, Blogger Sandra K said...

It's May-June, here.

At May 14, 2009 7:44 PM, Blogger The Neurocritic said...

It's May everywhere!

Your latitude is a bit lower than Greenland's...

At May 14, 2009 8:24 PM, Blogger Silver said...

It's interesting when you then look at this.

May is never, ever my favorite time of year; I take a lot of extra shifts and I can't get anyone admitted around here...

(Note latitude.)

At May 15, 2009 6:51 AM, Anonymous Anonymous said...

Huh. That's very interesting. I would have assumed that the depths of winter would trigger a rise in suicides, especially among SAD sufferers. Or is it just that when people are feeling depressed in the winter, they don't have the energy to actually attempt suicide?

I know from my own case, the short days and lack of light from Dec-Feb leave me in an extended emotional low. But it was July when I made a suicide attempt. (An obviously unsuccessful one.)

At May 15, 2009 8:05 AM, Anonymous B. D. Colen said...

There are two possibilities here:
The first is the most obvious - call it the Al Pacino effect; expose someone to 24 hours of daylight for too long and the crumble from lack of sleep;

The second is that when depressives awake from their long winter nap and are bathed in 24 hours of sunlight they gain the strength to end it all.

At May 15, 2009 4:09 PM, Blogger The Neurocritic said...

Silver - Thanks for the link, I was not familiar with that study.

Anonymous - I'm glad you're still with us. I hope you're getting treatment that helps your SAD.

B.D. Cohen - As to the second possibility, very few of the suicides had been diagnosed with an affective disorder (3.8%). Alcoholism or alcohol intoxication were more common (15.8%). It could be the case, however, that depression and bipolar disorder were underdiagnosed.

At May 15, 2009 4:18 PM, Blogger The Neurocritic said...

Here's a link to some interesting information on Light and Dark Therapy.

At May 19, 2009 9:40 PM, Anonymous Anonymous said...

A pure speculation. Perhaps a large percentage of Greenland people are depressed all the time. However, in Winter, they can attribute the sadness to the bad weather, whereas in the Summer they cannot do so. So, it is during the Summer that they realize it's mostly internal. And that can be a painful realization.

At May 24, 2009 5:16 PM, Blogger Sandra K said...

Epidemiological studies - not just from Greenland, but Finland, Canada, Australia, Italy, many other locations - aren't "pure speculation," Anonymous #2.

Springtime is suicide season. Why? That's where speculation rides in.

At June 03, 2009 11:36 AM, Blogger Phoenixkidd said...

Interesting, I know that deprivation of sleep is a sure way to instigate neurotic or psychotic response. I should know with my bi-polar sister. Now I sleep in a room with blinds that let in tons of light, I know in Sunny Phoenix it is especially hard to sleep in Summer.

At July 22, 2009 2:42 PM, Anonymous woke said...

Recently a friend, upon learning I had spent the 18th year of my life in Thule deployed in USAF, asked me which season bothered me the most, summer=light or winter=dark.

My first response was summer-light. Then I told him that i believed it was the isolation that was the toughest.

And of course, being young and in the military, alcohol played a role also.

At October 08, 2009 12:10 PM, Anonymous Anonymous said...

I came across this post looking for data on whether the strength of the seasonal response corresponded more to the latitude of the sample or the latitude from which the population derived (high latitude in both cases here, but comparison between Victoria, NSW and Santiago Chile suggests the magnitude of response is lower in a low-latitude derived population.) The underlying hypothesis is that people from high latitudes are most prone to go into despair from frustration of desires when day length is long.

At October 11, 2009 7:05 PM, Anonymous Anonymous said...

Slate picked this up too:

Remember that Greenland had one of the world's lowest suicide rates until the 1970's, even though the sun is a little older than that. There is clearly something else going on.
Based on the data, it's equally possible that impulsiveness in general does increase in the summer, and the homicide rates examined didn't reach significance because the sample size is so small - they analyzed about 1/5 the number of homicides as suicides.

Personally, I think "seasonality" is a red herring - the difference in suicide rates from winter to summer is small compared to the huge increase in yearly suicides before and after 1970. According to the Slate article, most of those suicides are indigenous Inuit and many are teenagers, which means that the first wave of suicides in the 1970s were part of the first generation of Inuits to grow up in the communities formed after government mandated resettlement. This period of increased suicide also coincides with increased alcohol abuse among Inuit populations. Is sunlight really the most likely explanation here?

At October 12, 2009 1:03 PM, Blogger The Neurocritic said...

Thanks for linking to the Slate article, I hadn't seen it. I agree that social factors play a huge role in the increased suicide rate. Bjorksten et al. acknowledged that as well, concluding their article by stating:

"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."

At January 10, 2011 4:55 PM, Anonymous Anonymous said...

The problem is obvious. These were indigenous people living off the land and they were moved, against their will, into ugly, stark towns. Their freedom was taken away. Simple answer to the problem, let them go back to the bush and live off the land again. They will find meaning in life and stop killing themselves. The G60 policy is 100% to blame here.

At February 26, 2013 3:36 AM, Anonymous Michelle said...

Of course its not the sun causing the suicides. If it was the suicides would have been high in the past but they had the lowest rates 100 years ago. Duh


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