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Abstract
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Suicide is a significant medical and social problem around the world.1,2 It is estimated that over 800,000 people die by suicide each year around the globe and that there are many non-fatal suicide attempts for each suicide death. In some countries, suicide rates are increasing.1,2 For example, in the United States, the age-adjusted suicide rate increased 36.7% between 2000 and 2018 (10.4/100,000 to 14.2/100,000).2
Multiple biological and psychological mechanisms are involved in the pathophysiology of suicide.1-4 For example, childhood traumatic experiences are a risk factor for non-suicidal self-injury and suicidal behavior.4 Meteorological influences such as the ambient temperature may affect human behavior, including suicidal behavior.5-8
Several research reports indicate that a higher ambient temperature is associated with an increased risk of suicide.5-8 Page et al.5 studied the relationship between daily suicide counts and temperature in England and Wales and found that above 18 °C, each 1 °C increase in mean temperature was associated with a 3.8 and 5.0% rise in suicide and violent suicide, respectively. Using comprehensive data from multiple decades for both the United States and Mexico, Burke et al.6 found that suicide rates increase 0.7% in United States counties and 2.1% in Mexican municipalities for every 1 °C increase in monthly average temperature. Kim et al.7 examined the temperature-suicide relationship using data collected from multiple locations in 12 countries and found that the risk of suicide increased with the increasing ambient temperature. Kayipmaz et al.8 found that an increase in the ambient temperature leads to an increase in the number of suicides in Turkey. It has been proposed that the association between higher ambient temperature and increased risk of suicide is related to alterations in the serotonergic system, including a decrease in the levels of l-tryptophan, a precursor for serotonin.5,7,8
It is interesting to hypothesize that changes in testosterone levels may mediate the effect of the ambient temperature on suicidal behavior. Several animal and human studies conducted over the past decades have shown that an increase in the ambient temperature reduces testosterone secretion.9-12 For example, Gomes et al.9 observed that a high ambient temperature is detrimental to testosterone secretion in rams. Gesquiere et al.12 examined the effects of season and ambient temperature on testosterone levels in male baboons. The authors observed that testosterone levels were lower in months of high average daily maximum temperatures and suggested that their finding was a result of the direct impact of heat on testes. Some human studies have produced similar results.10,11 For example, a study of seasonal effects on blood testosterone concentration in a large sample of 32-44 y.o. U.S. military veterans found that testosterone levels peaked in December, a cold time of the year.10 Another research group reported that testosterone levels showed significant seasonal variation in men living in the north of Norway, with lower levels during the summer months.11
Several observations published over the past 15 years indicate that lower testosterone levels may be associated with suicidal behavior.13-16 In our study, we examined morning testosterone levels in male combat veterans with or without a history of suicide attempt...
Language: en |