Has Sperm Count Declined in the General Male Danish Population during the Last Several Decades？ A Study on the Relation of Sperm Count and Birth Year

It has been hypothesized that during the last several decades human sperm count has declined because of prenatal exposure to environmental chemicals. We examined the relation between semen.quality and birth year among 8608 men born from 1922 to 1971 and who from 1968 to t992 consulted 4 Danish medical centers because of barren marriage, Data were obtained from medical records and by a postal questionnaire to a subset of the population. The sperm concentration was significantly declining with increasing year of birth in 2 of the 4 centers, but this association disappeared when confounders were adjusted for. Within the subset of men born during 1955--1970 comprising 36% of the entire poputatlon we revealed a decrease of the average sperm concentration by 1.6 millionlml (95% CI: 0.7-2.5) per one advancing year of birth. This finding was consistent across all the 4 centers and robust to adjustment for effects of calendar period, season and duration of sexual abstinence. Effects of age were accounted for by restriction of the sample to men between 20 and 45 years. The findings are compatible with environmental impact in the prenatal period after 1955 but are far from unequivocal evidence that the sperm count in the general male Danish population has changed during the past decades.

Has Sperm Count Declined in the General Male Danish Population during the Last Several Decades?A Study on the Relation of Sperm Count and Birth Year

It has been hypothesized that during the last several decades human sperm count has declined because of prenatal exposure to environmental chemicals. We examined the relation between semen quality and birth year among 8608 men born from 1922 to 1971 and who from 1968 to 1992 consulted 4 Danish medical centers because of barren marriage. Data were obtained from medical records and by a postal questionnaire to a subset of the population. The sperm concentration was significantly declining with increasing year of birth in 2 of the 4 centers, but this association disappeared when confounders were adjusted for. Within the subset of men born during 1955~1970 comprising 36% of the entire population we revealed a decrease of the average sperm concentration by 1.6 million /ml (95% CI:0.7~2.5) per one advancing year of birth.This finding was consistent across all the 4 centers and robust to adjustment for effects of calendar period, season and duration of sexual abstinence. Effects of age were accounted for by restriction of the sample to men between 20 and 45 years. The findings are compatible with environmental impact in the prenatal period after 1955 but are far from unequivocal evidence that the sperm count in the general male Danish population has changed during the past decades.