Lead and Age Reduce The Fertilizing Ability of Sperm

Susan Benoff, MD, NYU School of Medicine, R01ES06100
Andy Wyrobek, Ph.D. and Brenda Ezkenazi, Ph.D., Univ. Cal. Berkeley, P42ES04705

Background: Human sperm are fragile creatures, but there are so many in a single ejaculate, odds are good that one will find the target-the egg. However, over the past 15-20 years, the scientific community has been alarmed over the drastic decreases in human sperm concentrations reported in some scientific publications. Environmental agents have been shown to reduce sperm concentrations and viability in laboratory animals. Increasing age is known to be a factor in fertility reduction in women in part because of the finite number of oocytes women have at birth. Lead is known to reduce fertility in animal models, but a direct link between lead exposure and human fertility has not been established.

Advance: In two separate studies published in the same issue of Human Reproduction, two NIEHS-supported teams reported the harmful effects of age and lead exposure on human sperm. In the study on age, semen volume, motility, and the ability to swim in a straight line declined with age. Although the sperm concentration remained relatively constant, these decreases in function suggest that fertility starts dropping when men are in their 20s and continues to diminish for the rest of their lives. In the lead exposure study, lead was measured in the seminal plasma of 140 partners of women undergoing in vitro fertilization. Men with higher levels of lead had decreases in sperm counts and were more likely to have damaged sperm less likely to fertilize an egg.

Implication: These results present clinicians with additional information to consider when evaluating couples with unexplained fertility. Given the need for sperm function tests to predict the outcome of in vitro fertilization attempts, and to help in determining the appropriate course of infertility treatment, infertility clinics should consider measuring lead in semen of the partners of women undergoing in vitro fertilization.

Citations:

• Benoff S, Centola GM, Millan C, Napolitano B, Marmar JL, Hurley IR. Increased seminal plasma lead levels adversely affect the fertility potential of sperm in IVF. Hum Reprod. 2003 Feb;18(2):374-83.

• Eskenazi B, Wyrobek AJ, Sloter E, Kidd SA, Moore L, Young S, Moore D. The association of age and semen quality in healthy men. Hum Reprod. 2003 Feb;18(2):447-54.

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