Local daily temperatures, thermal seasons, and suicide rates in Finland from 1974 to 2010

Abstract

Objectives: Suicide peaks in late spring and October are still seen in Finland among many countries. Weather factors have been suggested as explanations for these peaks, although with inconsistent results. Since the exact timing of these peaks varies each year, the length of daylight and changes in it seem inadequate as an explanation. We hypothesized that ambient temperature and the timing of thermal seasons might associate with suicide rate.

Methods: Suicide rates from three areas across Finland (N = 10,802) were analyzed with Poisson regression in six different models against variables calculated from the local ambient daily temperature, diurnal temperature range, and the duration from the onset of thermal seasons. Separate models for men and women were constructed.

Results: The temperature change over 5 days associated with the suicide rate of men in Helsinki region, or in other words, the lower the suicide rate was, the higher the temperature decrease had been. For women, the results were more inconsistent.

Conclusions: Our study is in line with some earlier studies which imply that impairment of thermoregulation might exist among suicide victims.

Fig. 1

Men’s monthly suicide rate suicides per 100,000 (black line), and smoothed (1 year window) temperature (gray line) in Oulu, Helsinki (Hki), and Jyväskylä (JKL) from 1974 to 2010. The right side vertical axis is for temperature (°C)

Fig. 2

Women’s monthly suicide rate suicides per 100,000 (black line), and smoothed (1 year window) temperature (gray line) in Oulu, Helsinki (Hki), and Jyväskylä (JKL) from 1974 to 2010. The right side vertical axis is for temperature (°C)

Fig. 3

Rate ratio (solid line), with 95 % confidence intervals (dash lines), for the suicide rate of men in Helsinki in relation to the change in daily mean temperature during 5 days in Helsinki (60N, 24E), from 1974 to 2010

Fig. 4

Rate ratio (solid line), with 95 % confidence intervals (dash lines), for the suicide rate of women in Jyväskylä in relation to the number of days from the onset of thermal spring in Jyväskylä (62N, 25E), from 1974 to 2010

Fig. 5

Rate ratio (solid line) with 95 % confidence intervals (dash lines) for the suicide rate of men in Oulu in relation to the number of days from the onset of thermal winter in Oulu (65N, 25E), from 1974 to 2010