Soy foods, low sperm count linked, says study

July 24th, 2008 - 3:47 pm ICT by IANS  

Washington, July 24 (IANS) Even eating half a serving of soy food daily could engender a lower sperm count among men, particularly the obese. The largest ever study examining the link between semen quality and phytoestrogens (plant compounds that behave like oestrogen), found that soy eaters had 41 million sperm per millilitre (ml) less than those who avoided soy products.

The normal sperm count ranges between 80-120 million per ml, the study conducted by Jorge Chavarro of Harvard School of Public Health, Boston and his colleagues revealed.

Isoflavones (daidzein, genistein and glycitein) are plant-derived compounds with oestrogenic effects that are found mainly in soyabeans and soy-derived products.

Animal studies have linked the high consumption of isoflavones with infertility in animals, but so far there has been little evidence of their effect in humans.

Chavarro and his colleagues analysed the intake of 15 soy-based foods in 99 men who had attended a fertility clinic with their partners to be evaluated for sub-fertility between 2000 and 2006.

They asked them how often and how much they had eaten in the previous three months; the foods included tofu, tempeh, tofu or soy sausages, bacon, burgers and mince, soy milk, cheese, yoghurt and ice cream, and other soy products such as roasted nuts, drinks, powders and energy bars.

The men were divided into four groups according to their intake of soy foods and isoflavones. After adjusting for factors such as age, abstinence time, body mass index (BMI), alcohol and caffeine intake and smoking, Chavarro found that men in the highest intake category had, on average, 41 million sperm/ml less than men who did not eat soy foods.

“Men in the highest intake group had a mean soy food intake of half a serving per day: in terms of their isoflavone content that is comparable to having one cup of soy milk or one serving of tofu, tempeh or soy burgers every other day,” he said.

The researchers found evidence that the association between soy food intake and sperm concentrations were stronger in men who were overweight or obese (72 percent of them were).

The study does not reveal why soy foods have this effect on sperm, but Chavarro speculates that increased oestrogenic activity may have an adverse effect on the production of sperm by interfering with other hormonal signals.

These findings were published online in Europe’s reproductive medicine journal, Human Reproduction Thursday.

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