Fresh research points to length of day as an unexpected possible contributor to rates of self-harm and suicide, writes MARINA MURPHY
UNDERSTANDING how length of day affects brain chemistry may help reduce the terrible human toll taken by suicide.
Researchers have found that the rate of self-harm rises as length of day increases, something that seems counter-intuitive to those of us who dread those long winter nights.
The longest day possible in the northern hemisphere, the summer solstice, is just around the corner, occurring on June 21st. The sun reaches its highest point in the sky at 5.45am on that morning, the point at which the days begin to shorten as the year progresses towards winter.
Countries at high latitudes have long summer days. In Ireland, daylight can last as long as 20 hours at the height of summer. In winter the reverse is true with very long nights. It is a commonly held belief that that depression and the rate of self-harm peak during the doom and gloom of winter.
A group of international researchers tested this by looking at how suicide rate varied with season. They studied the seasonal variation of all suicides in Greenland from 1968 to 2002.
The results show that, in fact, suicide rates peak in June and dip in December. The seasonal effect was most pronounced in the north of Greenland, where the sun does not set between the end of April and the end of August, according to the study in BMC Psychiatry.
It is thought that the explanation lies in the fact that production of the neurotransmitter serotonin in the brain is directly affected by daylight. Serotonin, popularly known as the body’s “feel-good hormone”, has many functions including the regulation of mood.
The authors speculate that light-induced imbalances in serotonin may lead to increased impulsiveness, which when combined with a lack of sleep, may explain increased suicide rates in the summer. There is already evidence that the amount of daily sunshine also affects production of melatonin, the sleep hormone, according to Dara Cannon, co-director of the Clinical Neuroimaging Laboratory at NUI in Galway. And, she says, there is a known relationship between melatonin and serotonin.
“It is incredibly interesting,” she says. “These observations have the potential to at least partly explain why there is a seasonal effect on suicide rates.”
Dr Cannon has previously used brain imaging techniques to study levels of serotonin in depressed patients. She says that there is evidence that greater hours of sunshine decrease the level of compounds that mop up serotonin in the brain.
The resultant increased serotonin levels should have a positive effect on mood. This is the effect sought when prescribing antidepressants. But some researchers have speculated that a spike in levels of serotonin with increasing daylight may give depressed people a sort of trigger, or motivational boost, to act on suicidal impulses.
Cannon points out that long daylight hours will be detrimental to a select group of people.
“We don’t yet know how to define who they are, but they are likely those who are already depressed, those at risk of depression or those who have a genetic defect in the mechanisms that control serotonin levels in the brain,” she says.
“The study also raises the possibility that there will be an effect of latitude and season on the efficiency of antidepressants that act on the serotonin transporter. However, the nature of these effects is not very well understood,” she adds.
Recent statistics (2007) from the National Office of Suicide Prevention show that Ireland has the fifth highest rate of youth suicide in the European Union. We top the table with Estonia, Finland, Latvia and Lithuania, all of which are at high latitudes, greater than 50 degrees north.
At the other end of the scale are countries, such as Malta and Greece, where daytime and nighttime hours are more or less balanced, no matter what the season.
The most recent data always shows that suicide has the greatest monthly variation of any cause of death. There were 27 per cent, 20 per cent and 37 per cent more suicide deaths than expected in Ireland in April, May and June, respectively, and 10 per cent, 25 per cent and 15 per cent fewer than expected suicide deaths in September, October and December respectively.