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Fish oil supplements linked to better testicular function

Men who took supplements had higher semen volume and testicular volume, and better hormone levels

Louise Prime

Tuesday, 21 January 2020

Healthy young men who said they took fish oil supplements had better testicular function, on several measures, than those who didn’t take fish oil supplements, in a study* from Denmark published in JAMA Network Open. The study authors said they did not believe that confounding could explain the association, although they could not show whether it was causal – and they said their findings need to be confirmed in well-designed randomised controlled trials (RCTs) among unselected men or in large prospective cohort studies.

The research team, led from the University of Southern Denmark, Odense, and the University of Copenhagen, pointed out that supplement intake of ω-3 polyunsaturated fatty acid has been found to improve semen quality among men with infertility, but it is unknown whether or not this also applies in healthy men. To address this, they analysed six years’ data from compulsory examinations to determine young Danish men’s fitness for military service – men were approached after the examination and invited to participate in a study of reproductive function, regardless of their fitness for military service, and 30% of those invited agreed.

The study authors reported that of the 1,679 participants, 98 men (5.8%) said they had used fish oil supplements during the past three months, of whom more than half (54.1%) said they had taken them on 60 or more days.

Compared with men who reported no intake of fish oil supplements, and after adjustment, men who took fish oil supplements but on fewer than 60 days had a semen volume that was 0.38ml higher (a non-significant difference) and those who took them on at least 60 days had a mean of 0.64ml higher semen volume (significant). Testicular volume was higher in supplement users compared with non-users, but only significantly so in those who took them on 60 or more days. Men who took fish oil supplements also had significantly lower levels of both follicle stimulating hormone (20% lower) and luteinizing hormone (16%). The researchers found no associations between other supplements and measures of testicular function.

They said: “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 ω-3 fatty acids in the supplements…

“To our knowledge, RCTs on intake of fish oil supplements have only been performed among men with infertility, and our findings need to be confirmed in well-designed RCTs among unselected men or in large prospective cohort studies.”

*Jensen TK, Priskorn L, Holmboe SA, et al. Associations of fish oil supplement use with testicular function in young men. JAMA Netw Open. 2020;3(1):e1919462. doi:10.1001/jamanetworkopen.2019.19462

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