Elevated levels of genistein and daidzein linked to improved fertility
NEW ORLEANS—Boosting the intake of soy protein may improve semen parameters and sperm DNA integrity in infertile men, according to findings presented here at the 62nd annual meeting of the American Society for Reproductive Medicine.
“It may be that the soy has a way of preventing oxidative stress. Isoflavones like genistein and daidzein function as antioxidants and this increased antioxidative activity can help regulate apoptosis,” said lead investigator GyunJee Song, PhD, a research scientist in the department of obstetrics and gynecology at the University of Rochester Medical Center in New York.
Epidemiological and experimental studies have shown that dietary or supplementary soy isoflavones may prevent a host of human diseases. Genistein and daidzein are two phytoestrogens in particular that function as selective estrogen receptor modulators. Recent studies have shown that, in vitro, the antioxidant activity of genistein may prevent sperm DNA damage induced by hydrogen peroxide to a greater extent than vitamin C or vitamin E.
Dr. Song and her colleagues recruited 48 men with abnormal semen parameters. All men had partners who had been trying to conceive for at least 12 months. The researchers used as a control group 10 men with normal semen analyses who within the previous 12 months had impregnated a woman. The mean age of the study population was 33 years and 90% were Caucasian. Dr. Song’s team used conventional semen analysis and semen aliquots were frozen to measure the sperm DNA integrity using sperm chromatin structure assay (SCSA).
Higher mean levels of dietary intake of genistein and daidzein were found in the fertile control group compared with the infertile men. The infertile group had genistein and daidzein intake of 527 and 241 µg/day, respectively, compared with 1,722 and 788 µg/day in the fertile controls.
Compared with men who had poor sperm DNA integrity, those with good sperm DNA integrity had higher levels of daidzein and genistein. Additionally, increased dietary intake of these proteins was associated with higher sperm count and greater sperm motility.
“For now we don’t know what the ideal dose is or what the upper limit may be for the benefits of these isoflavones in terms of sperm parameters,” Dr. Song said. “However, we know from observational studies of Asian populations that there is no risk from consuming soy-rich diets. Average intake of isoflavones in our study population was at least 20 times less than in Asian populations.”
Rebecca Sokol, MD, MPH, director of andrology and professor of medicine and obstetrics and gynecology at the University of Southern California Keck School of Medicine in Los Angeles, said the findings are intriguing and may have potential therapeutic implications. She cautioned that much more research is needed before infertile men are advised by urologists to increase their soy intake.
“A balanced intake of antioxidants is probably beneficial for good sperm function,” Dr. Sokol said. “However, isoflavones have weak estrogen-like effects. High levels of estrogens interfere with sperm function. Therefore, recommending antioxidant vitamins for men with infertility is probably a good idea, but suggesting that these men increase their soy intake cannot be recommended at this time.”