Study Links Soy to Lower Sperm Counts

Tuesday, July 29, 2008

Eating even small amounts of soy products may cut a man's sperm concentration, a study published online last Thursday in the journal Human Reproduction shows.

Of the 99 men enrolled in the study, those who said they ate the most soy had much lower sperm concentrations than those who reported eating no soy. Soy eaters had, on average, 41 million fewer sperm per milliliter than those who avoided soy products. That association held up after other factors potentially affecting sperm health, such as smoking, alcohol and caffeine intake, age, abstinence time and body mass index were considered.

Still, a man starting with an average sperm count (80 million to 120 million per milliliter) and experiencing such a reduction would measure well above the 20 million that is the minimum count within the normal range, says lead author Jorge Chavarro, a research fellow in the department of nutrition at the Harvard School of Public Health.

Consumption of the study's 15 soy-based foods, from miso soup and tofu to soy burgers, ice cream and energy bars, was low, an average of one serving every other day among the highest-consuming group.

Soy contains isoflavones, which have long been tied to infertility in animal studies.

The study is the largest to look at soy's effect on human male fertility; its findings conflict with those of previous studies, one of which found no relationship between the two and another that found soy consumption actually boosted sperm counts.

Given those conflicts, Chavarro says, "I think there is not enough evidence to reach any strong conclusion or advise men one way or the other on whether soy foods can affect their fertility."

-- Jennifer Huget

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