Evidence of deteriorating semen quality in the United Kingdom: birth cohort study in 577 men in Scotland over 11 years

Abstract

Objective : To determine whether the quality of semen has changed in a group of over 500 Scottish men born between 1951 and 1973. Design : Retrospective review of data on semen quality collected in a single laboratory over 11 years and according to World Health Organisation guidelines. Setting : Programme of gamete biology research funded by Medical Research Council. Subjects : 577 volunteer semen donors. Of these, 171 were born before 1959, 120 were born in 1960-4, 171 in 1965-9, and 115 in 1970-4. Main outcome measures : Conventional criteria of semen quality including semen volume (ml), sperm concentration (10 6 /ml), overall motility (% motile), total number of sperm in the ejaculate (10 6 ), and total number of motile sperm in the ejaculate (10 6 ). Results : When the four birth cohort groups were compared a later year of birth was associated with a lower sperm concentration, a lower total number of sperm in the ejaculate, and a lower number of motile sperm in the ejaculate. The median sperm concentration fell from 98x10 6 /ml among donors born before 1959 to 78x10 6 /ml among donors born after 1970 (P=0.002). The total number of sperm in the ejaculate fell from 301x10 6 to 214x10 6 (P=0.0005), and the total number of motile sperm in the ejaculate fell from 169.7x10 6 to 129.0x10 6 (P=0.0065). Conclusion : This study provides direct evidence that semen quality is deteriorating, with a later year of birth being significantly associated with a reduced number of sperm in adult life. Key messages: Key messages When men born in the 1970s were compared with men born in the 1950s, the total number of motile sperm in the ejaculate was reduced by almost 25% These data confirm previously published data from other countries that semen quality is changing, declining by about 2.1% per year Research is urgently required to examine the function as well as the number of sperm and to assess whether these changes are affecting human health and male fertility