A man's fertility may be affected by his weight, a new study shows. Men who are either too fat or too thin may find that they have lower sperm counts, often low enough to be classed as 'impaired fertility'. The study, undertaken by researchers in Denmark and published in the journal Fertility and Sterility, could lend weight to the possibility that high levels of obesity in Western societies may be contributing to fertility problems.
The researchers studied 1558 Danish men, comparing their sperm count to their body mass index (BMI - a measure of weight in relation to height). They found that men with either a low or a high BMI had differences in reproductive hormone levels as well as lower sperm counts than men of the recommended weight. Men with a low BMI (below 20) were, on average, found to have a 28 per cent lower sperm count and a 36 per cent lower sperm concentration than men with a normal BMI. Men with a high BMI (above 25) had a 22 per cent lower sperm count and 24 per cent lower sperm concentrations. It was also found that as the BMI increases, levels of testosterone - the male sex hormone - decreased too. Dr Tina Kold Jensen, leader of the research team, said that weight might not be the only factor. It is possible, she said, that the types of lifestyles that cause extremes in weight may also cause decreased semen levels. For example, she pointed out, lack of exercise and poor diet may also be important when looking at overweight men.
A second study warns that male fertility can also be affected by the type of bed men choose. Researchers from the University of Pennsylvania studied the use of waterbeds and a number of other 'lifestyle factors' in more than 650 infertile and 698 fertile American men. Dr Clarisa Garcia, leader of the research team, said that the study showed 'current alcohol consumption, electric blanket use and waterbed use were associated with a greater likelihood of infertility'. Men who used waterbeds were found to be more than four times likely to be infertile than non-users, while those who used electric blankets were more than seven times more likely.
The researchers speculate that infertility problems may be linked to increased sleeping temperature, as many waterbeds are also heated. But, they said, there were 'surprising' findings about hot baths, which don't appear to affect fertility at all. There was also no link found between infertility and the use of Jacuzzis, smoking, coffee, tea, being exposed to vibrations, or electric heaters. The research was presented at the annual conference of the American Society for Reproductive Medicine (ASRM).