Higher intake associated with decreased sperm concentration, not sperm motility and morphology.
WASHINGTON, D.C.—Higher intake of soy foods and soy isoflavones may be associated with lower sperm concentrations, data suggest.
Researchers at the Harvard School of Public Health in Boston conducted semen analyses in 100 men who presented to the Massachusetts General Hospital Fertility Center. The study population was 90% Caucasian and had a mean age of 36.3 years. Those with the highest soy food intake (median intake 0.5 servings per day) had 41 million sperm per milliliter less than men who did not consume any soy. Soy consumption, however, did not affect sperm motility and morphology.
Using a questionnaire, the researchers collected information on the intake of 15 soy-based foods that the men had consumed in the previous three months. The researchers determined the isoflavone contents for each food based on the standards developed by the U.S. Department of Agriculture. The researchers found an inverse association between soy food intake and sperm concentration that remained significant after adjusting for age, smoking, abstinence time (no ejaculation), BMI, and caffeine and alcohol intake. Results for individual soy isoflavones were similar to the results for soy foods.
“We found that men were mainly eating tofu and miso soup as well as more subtle things like granola bars containing soy,” said lead investigator Jorge Chavarro, MD, a research fellow in the department of nutrition. “I don’t think we should tell people to avoid soy. The available evidence is not strong enough to recommend avoiding soy for fertility reasons. On the other hand, it seems to have important cardioprotective effects. However, if a man is obese and also has fertility problems and happens to consume high amounts of soy foods, then it might be a good idea to advise him to reduce his soy food intake.”
Dr. Chavarro presented study findings here at the annual meeting of the American Society for Reproductive Medicine.
Steven Ory, MD, immediate past president of ASRM, said the new findings are provocative. “A large number of lifestyle factors may influence a patient’s fertility,” said Dr. Ory, who is with IVF Florida Reproductive Associates in Margate, Fla. “It is important that physicians take this into account when seeking their histories to provide the most appropriate advice.”