According to statistics, it is observed that women outlive men in Western countries, and scientists have traditionally pointed to riskier behavior on the part of men as the reason why. A new study suggests that there may be more to it than that. Another reason for the earlier demise of men may be that they are more prone to parasitic infections.
In a report on the study, Ian P. F. Owens, from Imperial College London, writes, "In those species where males die younger than females, the males suffer a disproportionately high rate of parasitism. The authors also show that male-biased parasitism is the general rule among mammals, and that it is most extreme in those species where male-male competition for mates is most severe. Taken together, these findings suggest that male-biased mortality occurs not only as a result of death through risky behavior, but also because males are more susceptible to parasitic diseases."
What could make men more prone to infections? Owens believes testosterone may play a key role. The male hormone is well-recognized as an immunosuppressant, and studies have shown men who are castrated (and thus no longer produce testosterone) live about 15 years longer than men who are not castrated. Testosterone may suppress the immune system, he continues, by changing the way men's bodies allocate important resources, such as taking energy away from the immune system and using it for other purposes.
Another explanation for the increased risk for parasitic infections among males, however, may simply be that men are bigger than women and thus provide a larger target for parasites. Owens notes in mammalian species where females are larger in size than males, it is the females who are more susceptible to parasitic infections.