If the little soldiers inside the testicles are fast swimmers, it could give men an evolutionary advantage, according to a new study.
There is no clear-cut answer to why men with high sperm quality tend to live longer. Not much evidence supports the view that the link can be attributed to the man’s general health.
“Our survey showed that men with a high death rate did not die from typical lifestyle-diseases such as lung cancer and alcohol-related diseases,” says Professor Tina Kold Jensen of the Department of Environmental Medicine at the University of Southern Denmark, where the study was conducted.
“So our hypothesis is that although good sperm quality can be linked to a low death rate, it is not necessarily an indicator of a healthy lifestyle.”
The research team has collected sperm samples from 51,543 men gathered from the Danish sperm analysis laboratory, covering the period 1963-2001. The men had delivered their sample because they had problems with getting their partners pregnant – so the reason could either be that they were infertile themselves or their partner was.
The researchers registered the men's death rates over the 38-year period and then compared the quality of their sperm samples. 1,475 men died in the period.
There was a clear correlation: men with high-quality sperm had a significantly greater likelihood of living longer than those with low-quality sperm. The figures were then compared to the general death rates, which also showed that men with low-quality sperm have a shorter than average lifespan.
Sperm quality is defined by the number of sperm per milliliter. In general, if a man has more than 40 million sperm per milliliter, he has a ‘high’ sperm quality and has good reproduction odds. In the study, a sperm count of less than 25 million per millimeter was regarded as ‘low’ sperm quality.
It is, however, not possible to tell how much longer men with good sperm live, since many of the participants are still alive.
Another point of uncertainty is whether the correlation between good sperm and low death rates should be put down to biological or social factors. According to Jensen, the link could to a certain degree be attributed to testosterone.
Sperm quality has traditionally been associated with testosterone levels, where a high sperm count equals a high level of testosterone and vice versa. If the hypothesis that testosterone is a deciding factor for death rates holds true, it would make sense that high sperm quality equals a low death rate, according to Jensen.
“I believe that testosterone plays a major part in determining survival skills,” she says. “For instance, men with testicular cancer receive testosterone injections as part of their treatment, and testosterone is also important hormone for men who workout as it boosts their energy levels.”
The study was published in the American Journal of Epidermiology.