For the past two decades, at least, there have been concerns over declining sperm count. This is an important public health issue for a number of reasons. While low sperm count is only loosely correlated with male infertility, it has also been shown to be associated with all-cause mortality, morbidity, testicular cancer and various other disorders.
Levine and colleagues conducted a meta-analysis of 185 studies covering 38 years, which looked at the semen of 42,935 men in total. Adjusted meta-regression analysis showed that the sperm concentration of semen had declined significantly between 1973 and 2011 (slope of -0.64, 95% CI -1.06 to -0.22, p=0.003). On average, the mean sperm concentration had declined by 0.75% per year, with an overall drop of 28.4% since 1973. Sub-group analysis found significant decline among both unselected men (who were not selected by whether they were fertile or not, such as in screening for military service) and fertile men (who were known to have conceived a pregnancy) from Western countries (North America, Europe, Australia and New Zealand). The drop was most pronounced in unselected Western men who had declined by 1.5% per year, with an overall drop of 52.4%.
The results for all men, as well as the sub-groups, were similar when the analysis was repeated using studies conducted post-1995, suggesting that the decline was not ‘levelling off’.
Numerous factors have been suggested for contributing to such a decline, with studies showing plausible associations between sperm count and environmental oestrogens, pesticides, heat, and lifestyle factors, such as diet, stress, smoking and BMI. The authors suggest that a declining sperm count may be “a canary in the coal mine” for male health – and there is a pressing need for further research into its causes.
— Peter Chilton, Research Fellow
- Levine H, Jørgensen N, Martino-Andrade A, et al. Temporal trends in sperm count: a systematic review and meta-regression analysis. Hum Reprod Update. 2017; 1-14.