Sunlight linked to summer suicide spike

STOCKHOLM, Sweden, May 8 (UPI) -- Suicide rates in Greenland increase during the summer, peaking in June, perhaps due to the insomnia caused by incessant daylight, researchers in Sweden say.

The study, published in the journal BMC Psychiatry, finds there was a concentration of suicides in the summer months, and this seasonal effect was especially pronounced in the north of the country -- an area where the sun doesn't set between the end of April and the end of August.

Study leader Karin Sparring Bjorksten of the Karolinska Institutet in Sweden and colleagues studied the seasonal variation of suicides in all of Greenland from 1968-2002.

The researchers finds most suicides occurred in young men and employed violent methods, such as shooting, hanging and jumping. No seasonal variation in alcohol consumption was found.

The authors speculate light-generated imbalances in turnover of the neurotransmitter serotonin may lead to increased impulsiveness that, in combination with lack of sleep, may explain the increased suicide rates in the summer.

"People living at high latitudes need extreme flexibility in light adaptation. During the long periods of constant light, it is crucial to keep some circadian rhythm to get enough sleep and sustain mental health," Bjorksten says in a statement. "A weak serotonin system may cause difficulties in adaptation."