Examining the impact of excess weight on semen quality
A recent systematic review and meta-analysis published in the International Journal of Obesity, conducted by researchers in China, has revealed the profound impacts of obesity and overweight on male fertility. This study delves into the association between Body Mass Index (BMI) and semen quality, indicating significant adverse effects, particularly in men with more severe levels of obesity.
Approximately 15% of couples of reproductive age worldwide face infertility issues, with male factors, notably poor semen quality, contributing to 20–70% of these cases. Over recent decades, a marked decline in semen quality has been noted globally. For instance, significant decreases in total sperm count and sperm concentration were observed from 1973 to 2011 in Western nations, and from 1981 to 2019 in China. This decline is influenced by various factors including age, lifestyle, and environmental conditions. An increase in abnormal BMI has been pinpointed as a potential risk factor amidst these changes. Previous studies have linked obesity to reductions in semen quality, but results have varied due to differences in BMI classifications and other methodological limitations.
To address these inconsistencies and provide clearer insights, the researchers included data from 50 human studies, involving a total of 71,337 men aged between 26 and 44 years. These studies were sourced from Embase, PubMed, and Web of Science and categorised men based on their BMI: under 25.0 kg/m² as the reference group, 25.0–29.9 kg/m² as overweight, and over 30.0 kg/m² as having obesity. The studies examined various semen parameters such as volume, sperm concentration, motility, total sperm count, and morphology. Men were also categorised based on their fertility status into general, infertile or sub-fertile, and suspiciously sub-fertile groups.
The analysis, employing statistical tools like the random effects model, Cochran’s Q tests, and I² statistics, demonstrated that obesity was associated with significant reductions in several key semen parameters. Men with obesity, for instance, showed reductions of 0.24 ml in semen volume, 19.56 × 10⁶ in total sperm number, and decreases in both total and progressive motility. Men with overweight experienced milder declines, which were not as widespread across different semen parameters.
The study also highlighted that the detrimental effects of obesity on semen quality varied across different global regions, including America, Asia, and Europe, suggesting regional differences in lifestyle and environmental factors could influence the degree of impact. Furthermore, the findings were consistent across different methods of semen assessment, reinforcing the robustness of the results.
Despite its strengths, such as a large sample size and unified BMI classifications, the study faced limitations related to potential inaccuracies in aggregated data and the BMI’s inability to distinguish between muscle and fat mass. Additionally, the traditional semen parameters used might not fully reflect the functional capacity of sperm.
In conclusion, the analysis confirmed a significant association between higher BMI and poorer semen quality, with more severe impacts observed in men with higher obesity classes. These findings emphasise the importance of maintaining a healthy weight to support male reproductive health and suggest that future studies should explore broader reproductive implications of obesity using more comprehensive indicators of sperm health and function.
