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Back in November of 2014, I wrote Sunshine and Suicide about a large, 40-year study linking increased suicide risk to sunny days. The risk seemed highest on the first sunny day after an overcast period, which made sense, as the highest rates of suicide occur in the springtime. As sunny days collect in a longer row (more than 10), the suicide rate seems to drop.
However, sunshine might not be the only climate factor associated with these sunny days. In fact suicide rates also go up as the ambient temperature increases. Dr. Jui-Feng Tsai found this association in Taiwan, and Maes et al noted the increase in violent suicide happening as temperature increases in other countries.
The Taiwanese data is particularly striking. In a 1995 heat wave, suicides went up by 46.9%, such that each increase in temperature of 1 degree C led to a 3.8% increase in suicide. The correlation was much stronger between temperature increases and suicide over the period studied (1991-2010) than economic factors such as unemployment rates. In addition, rainfall and associated cooling seemed to be protective, moreso for men than for women.
What could be the mechanism? How could a higher temperature lead to self-harm? Well, cooler temperatures actually change the shape of platelets, causing them to secrete serotonin. Low serotonin levels are definitely associated with violent suicide, so cooler temperatures could mean there’s a higher level of serotonin in the blood and therefore less violent suicide. However, the actual temperature is not as much of a risk factor as the change in temperature, which makes me believe there's more to it than just a serotonin issue.
If increases rather than sustained high temperature cause a higher risk of suicide, it makes you wonder about blazing hot areas where people spend most of the time indoors in air conditioning, then come out into the ambient air. And what about people who go swimming for exercise or recreation? Is there a higher rate of suicide or violence among cold ocean swimmers who experience vast temperature changes than those who take a lengthy dip in warm backyard pools? How about regular steamy sauna users in the wintertime in the far north?
The linkage to temperature increase could also be why the first few sunny days lead to a higher risk of suicide in the sunshine and suicide study, whereas more than 10 days in a row is not. Since the data in that study was collected from 1970-2010, it would be fascinating to go back and see if temperature increases were just as strongly correlated with suicide as a sudden increase in sunshine was to see if sunshine really is a factor after all.
Perhaps most interesting is that these climate changes have much more effect on the suicide rate in these studies than something like unemployment, which is traditionally thought to be a risk factor for suicide. Sometimes what seems like common sense isn’t as sensible as we thought.
Image credit: Flickr Creative Commons
Copyright Emily Deans MD
