Associations of Fish Oil Supplement Use With Testicular Function in Young Men

This cross-sectional study examines the associations of fish oil supplement intake with testicular function as measured by semen quality and reproductive hormone levels in young men in Denmark. Importance Many young men have poor semen quality, and the causes are often unknown. Supplement intake of omega-3 polyunsaturated fatty acid has been found to improve semen quality among men with infertility, but the association with semen quality among healthy men is unknown. Objective To determine if intake of omega-3 fatty acid supplements is associated with testicular function as measured by semen quality and reproductive hormone levels among healthy men. Design, Setting, and Participants This cross-sectional study included young Danish men from the general population recruited between January 1, 2012, and December 31, 2017, at compulsory examinations to determine their fitness for military service. Young unselected men were approached after the examination and invited to participate in a study of reproductive function, regardless of their fitness for military service. Data analysis was conducted from September 1, 2018, to June 30, 2019. Exposures Intake of supplements, including fish oil, during the past 3 months. Main Outcomes and Measures Semen quality, measured as volume, concentration, total sperm count, percentage of morphologically normal spermatozoa, and motility, and serum reproductive hormone levels, measured as follicle-stimulating hormone, luteinizing hormone, testosterone, free testosterone, and inhibin B levels. Results Among 1679 young Danish men (median [interquartile range] age, 18.9 [18.7-19.4] years) recruited to participate, 98 men (5.8%) reported use of fish oil supplements during the past 3 months, of whom 53 (54.1%) reported intake on 60 or more days. After adjustment and compared with men with no supplement intake, men with fish oil supplement intake on fewer than 60 days had semen volume that was 0.38 (95% CI, -0.03 to 0.80) mL higher, and men with fish oil supplement intake on 60 or more days had semen volume that was 0.64 (95% CI, 0.15 to 1.12) mL higher (P for trend < .001). Similarly, testicular size in men with supplement intake on fewer than 60 days was 0.8 (95% CI, -0.2 to 1.9) mL larger and in men with fish oil supplement intake on 60 or more days was 1.5 (95% CI, 0.2 to 2.8) mL larger compared with men with no supplement intake (P for trend = .007). After adjustment, men with fish oil supplement intake had a 20% (95% CI, 9%-31%) lower follicle-stimulating hormone level and 16% (95% CI, 8%-24%) lower luteinizing hormone level compared with men with no supplement intake. There were no associations of intake of other supplements with measures of testicular function. Conclusions and Relevance These findings suggest that intake of fish oil supplements was associated with better testicular function, which is less likely to be due to confounding by indication, as no associations of intake of other supplements with testicular function were found. This cross-sectional study did not examine the actual content of omega-3 fatty acids in the supplements; therefore, these findings need confirmation in well-designed randomized clinical trials among unselected men. Question Is intake of fish oil supplements associated with testicular function as measured by semen quality and reproductive hormone levels among young healthy men? Findings In this cross-sectional study including 1679 young men in Denmark, fish oil supplements were associated in a dose-response manner with higher semen volume and total sperm count, larger testicular size, a higher calculated free testosterone to luteinizing hormone ratio, and lower follicle-stimulating hormone and luteinizing hormone levels after adjusting for confounders. Meaning These findings suggest that healthy men may benefit from intake of fish oil supplements, but a well-designed randomized clinical trial among unselected men is warranted.