Their analysis of data collected from 1938 to 1990 indicates that sperm densities in the United States have exhibited an average annual decrease of 1.5 million sperm per milliliter of collected sample, or about 1.5 percent per year, while those in European countries have declined at about twice that rate (3.1 percent per year).

The study was conducted by epidemiologists Shanna Swan, Eric Elkin and Laura Fenster of the California Department of Health Services. It appears in the November issue of Environmental Health Perspectives, the monthly scientific journal published by the National Institute of Environmental Health Sciences.

Since the early 1930's, there has been considerable interest in declining semen quality as a key predictor of male reproductive dysfunction. The vast majority of studies designed to answer this question have focused on sperm density - the number of sperm contained in one milliliter of sample. (One milliliter is approximately 1/30th of an ounce.)

Despite enormous differences in data collection methods, study population and time period, most studies have come to the same conclusion - that sperm density has declined. In fact, a 1992 review of 61 such studies (Evidence for decreasing quality of semen during past 50 years, E. Carlsen, A. Giwercman, and N. Skakkebaek, British Medical Journal, vol. 305, page 609) revealed a steady decline, from 113 million sperm per milliliter in 1938 to 66 million in 1990, or about 1 million sperm per milliliter per year.

However, these studies did not take into account such factors as the age of the subjects, the length of abstinence prior to sample collection, and method of sample collection, each of which can influence the ob
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Contact: John Peterson
Peterso4@niehs.nih.gov
(919) 541-7860
NIH/National Institute of Environmental Health Sciences
24-Nov-1997