Current risk factors for male infertility and semen parameters: an umbrella review of systematic reviews and meta-analyses.
Plain-language summary
This umbrella review (a review of other reviews) set out to catalogue what damages male fertility. It gathered 43 systematic reviews and meta-analyses published between 2000 and 2025, covering 67 possible risk factors and 249 separate estimates of effect. Each estimate was rated with GRADE, a standard scoring system that asks how much confidence the evidence itself deserves, judging things like how well the studies were run, how consistent their results were and how large the effect was. Ratings run from very low to high. Not one of the 249 estimates here reached high certainty. Just over half, 54.6%, came out very low, 23.7% low and 21.7% moderate. Within those limits, the pattern was that type 1 diabetes, hyperthyroidism, lupus, chronic prostatitis and metabolic syndrome were linked to worse semen measures. Metabolic syndrome means a cluster of conditions that together raise heart-disease and diabetes risk: a large waist, high blood pressure, high blood sugar, high triglycerides and low HDL (good) cholesterol. The same pattern held for obesity, sleep disorders and smoking, exposure to pollutants such as lead and organophosphates, some medications including SSRIs, and some viral infections. Regular exercise, eating nuts and a diet built on vegetables, fruit, fish, whole grains and olive oil went the other way. The authors are explicit that most of these are associations rather than proven causes.
Key findings
- Type 1 diabetes, metabolic syndrome, hyperthyroidism, lupus and chronic prostatitis were linked to a higher chance of abnormal semen measures.
- Obesity, sleep disorders and smoking were linked to lower semen quality, as were pollutants such as lead and organophosphates, medications including SSRIs, and several viral infections.
- Regular exercise, eating nuts and a diet built on vegetables, fruit, fish and whole grains were linked to better semen quality.
- Of 249 effect estimates rated for certainty, none reached high: 54.6% were rated very low, 23.7% low and 21.7% moderate.
How to analyze the study yourself
- Study type
- Systematic reviews synthesize existing evidence but cannot establish causality on their own.
- Population
- The review included studies on men with infertility or abnormal semen parameters.
- Funding
- Not reported
- Watch for
- This study found that a long list of conditions, exposures and habits tracks with worse semen quality, but that the evidence behind every single item on the list is rated moderate at best and usually much weaker. If you are working on fertility, the items with the most support and the least downside are the familiar ones: regular exercise, not smoking, keeping weight in a healthy range, sleeping properly, and a diet that includes nuts.