Scientists report that men’s average total testosterone levels have fallen markedly over the past half-century, citing a broader shift in male reproductive health. Data presented at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in London shows total testosterone levels decline by 54% between 1972 and 2019. Researchers describe the change as substantial and say it raises concerns about male fertility, framing it as a potential “major crisis in male reproductive health.” The analysis links the decline to trends in obesity and diabetes, suggesting these conditions may play a role in lower testosterone levels, though the report does not specify the extent of causation from each factor. The findings are based on trends compiled from available measurements across decades, rather than tracking a single cohort over time. The work is discussed in the context of ongoing public health concerns and reproductive outcomes, with researchers calling for attention to metabolic health and its possible effects on male hormone function.