A meta-analysis pooling 185 studies found that sperm concentration in men from North America, Europe and Australia fell by 52.4 per cent between 1973 and 2011. An updated analysis in 2022 extended the finding to South America, Asia and Africa, and reported that the rate of decline appears to have accelerated since 2000.
No single cause has been established. The candidates under investigation are the ones you would expect — endocrine-disrupting chemicals, obesity, smoking, heat, sedentary work — and the honest position is that the trend is far better documented than its explanation.
