News from: COLUMBIA-PRESBYTERIAN MEDICAL CENTER
Contacts: Karin Eskenazi or Ruth Flaherty, 212/305-5587
FLUCTUATIONS IN SPERM COUNTS CORRELATE WITH FLUCTUATIONS IN BIRTH RATES
Role of male reproductive function in fertility may be underappreciated
NEW YORK, NY, FEBRUARY 12, 1997 -- Researchers at Columbia-Presbyterian Medical Center have found that population-wide sperm counts vary significantly from year to year, and that these variations coincide with yearly changes in birth rates. The findings, to be published in the March issue of the Journal of Urology, may also explain why previous fertility studies have concluded that sperm counts around the world are declining.
"This is an important finding, since it establishes sperm counts as an index of fertility," says the principal investigator, Harry Fisch, MD, Director of the Male Reproductive Center, Department of Urology, Columbia-Presbyterian Medical Center. "The study also shows that male reproductive function is a much more important factor in fertility than was previously understood."
In the study, the researchers analyzed data from 660 men who banked semen in a Roseville, Minn., sperm bank between 1971 and 1994 (the longest interval over which semen analysis data have been collected in a single site in the United States). The data were then correlated with regional birth data from the National Center for Health Statistics.
Average sperms counts fluctuated widely during these years, reaching a high of 123 million sperm per ml in 1980 and a low of 46.5 million sperm per ml in 1974. The fluctuations were found to coincide with changes in birth rates in Minnesota and in the United States as a whole.
Earlier studies have established a link between sperm counts and pregnancies in individuals. The current study now suggests that "changes in population-based sperm counts influence population-based birth rates."
Fisch and his colleagues do not know why sperm counts vary so greatly from year to year. They speculate that "heat may play a significant role. It is known that mild changes in scrotal temperature can decrease sperm counts. Our data, consistent with other reports, revealed that sperm counts fluctuate by season, with the highest sperm counts in the winter months... It is certainly possible that yearly temperature and climate changes may affect annual sperm counts in a similar manner as seasonal changes affect sperm counts."
The findings may influence the way researchers interpret male fertility studies. "While we found an upward trend in sperm counts for the last 24 years, perhaps more significantly, our data revealed that mean sperm counts varied from year to year," Dr. Fisch writes. "In fact, the year-to-year variability was so great it became apparent that the overall linear trend with time was strongly dependent on the year in which the study was initiated."
If the current study had been initiated in 1977, when sperm counts were high, instead of 1971, when counts were low, "we would have likely reported a decrease in sperm counts with time" Dr. Fisch reports. This would explain why several studies have reported a precipitous decline in sperm counts in recent years. According to Dr. Fisch, "it is possible that different conclusions ... would have been reached if more years were studied."
Dr. Fisch's co-authors include Howard Andrews, PhD, James Hendricks, MD, Erik T. Goluboff, MD, John H. Olson, MD, and Carl A. Olsson, MD.
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