Would you predict suicides increase in the sunshine/summer or darkness/winter?
Obviously, if I'm asking...
A Greek study-- and Greece has one of the lowest suicide rates in the world, about 5/100,000 (U.S. is about 17) with two major findings:
1. Suicides in the northern hemisphere, across 18 very diverse countries (Europe, Eastern Europe, Japan, North America,) peak in May/June, with a relative risk 1.08-1.5.
2. This peak is actually due to the amount of sunshine. More sun=more death.
#2 seems a stretch to me, so I looked it up further. Wow.
Same guys, find that there was no relationship between suicide and that day's sunlight; but there was a strong correlation with the past days sunlight. There were several specific sun/day-suicide interactions, but in general for males that past 8 days and the day before, and for females that past 4 days (but not he day before) were correlated to increased risk.
If you consider that the solar radiance in June is 26 MW/m2, and December is 6 MW/m2, then the risk of suicide increases 3% for every 1 MW/m2.
Others have found the same. An illustrative example is the Chile study finding the springtime peak of suicides, but this effect was absent in the north, which is closest to the equator and thus has the least seasonal variability (Chile is a strip that runs up and down the western part of South America.) Interestingly, other equatorial regions have failed to find seasonal suicide links (e.g. Singapore); some have even identified a reverse pattern in the southern hemisphere. And urban areas seem to have a less pronounced or absent effect.
This is all quite interesting, but in order for it to be useful we have to show that there isn't another obvious explanation. Here's one: people kill themselves in June because there are more available tools. Jumping off a building, outdoor hanging, drowning, all prefer better weather. For example, you don't mull jumping off a building during a week of rain.
Now you could counter that such a suicidal person would simply come up with something else (e.g. OD) but that's not what happens; suicides are very specific and personal acts. The jumper doesn't instead use a gun. (Consider that people with multiple suicide attempts use the same one or two methods each time.) If two methods are similar, however, then I think such a move could happen. But if the person is considering drowning, then an OD is probably not an option, because drowning means something, it ihas unconscious significance, and that can't be ignored.
I might even propose that non-OD and non-self-cutting suicides are just as much about the act as about the desire to die. When you get drunk and then stab yourself in the abdomen 45 times, you're communicating something as well as trying to die.
Following from this, it has been observed that there is no seasonal pattern to non-weather related methods: cutting, OD, gassing, (i.e. non-violent methods). There's no seasonality (skew towards winter) to jumping in front of a German subway, which is thankfully free of sunlight's evil effects.
So if it rains for a week, instead of moving to another completely different suicide method, I believe they would simply postpone (i.e. continue to ruminate about it) their attempt, unless a similar method is available.
BTW, this is about completed suicide, not suicidality or suicide attempts, for which I have no idea about the seasonality.
I bring this up because of the discussions I've had, especially with the residents at my hospital, on the extent of volitional control in suicide. I say it is a cognitive process and not necessary outcome of a disorder, and the idea that sunlight or weather can influence the timing or method of a suicide goes along with that.