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Scientists debate whether sperm counts are really falling

Janice Hopkins Tanne, New York

The possible worldwide decline in sperm counts sparked lively debate at a symposium last week entitled Hazardous substances and male reproductive health, which was sponsored by the New York Academy of Medicine and the Mount Sinai School of Medicine in New York.

A reported decline in sperm counts of around 1% a year between 1930 and 1990 attracted wide attention when it was reported by Dr Niels Skakkebaek, from the Rigshospitalet in Copenhagen (BMJ 1992;305:609-13). However, a reanalysis of data in the paper showed there was no worldwide decline, said Dr Harry Fisch of the Male Reproductive Center at Columbia-Presbyterian Medical Center in New York, although there was considerable yearly and geographical variation (Fertility and Sterility 1996;65:1044-6). Most of the data between 1935 and 1970 are from the United States, where sperm counts were high, so what seems to be a decline is more likely to be a geographical variation when other areas with lower sperm counts are added to the study. "You will find a decline if you ignore the geographic data," he said. Furthermore, he said, measurement techniques varied from laboratory to laboratory and the duration of abstinence before giving a sperm sample also varied in the studies considered in the Skakkebaek paper.

The decline is real, argued Dr Shanna Swan of the California Department of Health Services. She also reanalysed the data, included newer data up to 1996, and found that sperm counts declined 1.5% per year in the United States and about 3% per year in Europe but not in non-Western countries.

The answer may come from a study Dr Skakkebaek is coordinating, enrolling 300 men at each of four centres in Europe, four in the United States, and one in Japan, plus studies of military conscripts in Denmark and Finland. Preliminary results suggest that suboptimal semen quality is very common among young men, he said.

"There's something going on out there. We don't know quite what it is, but certainly something has changed. Powerful data cry out for explanation," said Dr Philip Landrigan, head of the department of community and preventive medicine at Mount Sinai School of Medicine in New York. He cited reproductive abnormalities in wildlife, a 68% increase in testicular cancer in the United States, a doubling of the incidence of hypospadias between 1972 and 1985, the possible decline in sperm count, and a small but significant decrease in the ratio of male to female births.

Other problems that may be related to male reproductive health include delays in achieving conception, spontaneous abortion, low birth weight, and even developmental disorders and cancers in offspring. In the United States there are 80,000-90,000 potentially harmful chemicals in the home and work environment, among them 17,000 registered pesticides. Little is known about their effects on male reproductive health.