Fish oil supplements could make men’s testicles bigger and boost their sperm count, a study claims.
Men who took the pills, which contain omega-3 fatty acids, were found to have testicles 1.5ml larger and to ejaculate 0.64ml more sperm, on average.
The men, who had an average age of 18, were included as regular supplement-takers if they had consumed fish oil for at least 60 out of the past 90 days.
Larger testicles and more sperm creation is linked to higher testosterone levels and better fertility, although the study did not test how fertile the men were.
The experiment was described by scientists as ‘well-conducted’ and ‘insightful’ but it was clear that it did not prove fish oil makes men more fertile.
Researchers from the University of Southern Denmark did their study using 1,679 young Danish men going through military fitness testing.
In Denmark military service is mandatory for all healthy men over the age of 18, so the men in the study were not yet soldiers.
Each of the men were screened for STIs, had physical exams, gave sperm samples and then answered questions about their diets and lifestyles.
If someone was considered a regular fish oil supplement user, the research found, they produced millions more sperm in an average ejaculation.
The researchers wrote in their paper: ‘Fish oil supplements were associated … with higher semen volume and total sperm count, and larger testicular size.’
Ninety-eight men in the study said they took fish oil supplements regularly, while another 95 took vitamin D or C supplements.
Men in the fish oil group were less likely to have fertility problems, which were judged against the World Health Organization’s low sperm count limit of 39million sperm per ml of semen.
The scientists found that 12.4 per cent of the men who took fish oil supplements (12 out of 98) had sperm counts below the WHO’s measure.
This compared to 17.2 per cent (192 out of 1,125) men who took no supplements.
And the longer someone had been taking supplements for, the more sperm they were likely to produce.
The researchers added that, based on a model fit and healthy 19-year-old: ‘Total sperm count was 147million for men with no supplement intake, 159million for men with other supplement intake, 168million for men with fish oil supplement intake on fewer than 60 days, and 184million for men with fish oil supplement intake on 60 or more days.’
The study did not give exact measurements for men’s testicle volume or sperm volumes – they only compared the two groups.
And the scientists could not explain why – if it was true – the fish oil improved sperm quality.
It was also not clear whether increased sperm volume was caused by – or caused – the change in testicle size.
Scientists not involved with the research said the study had been well-conducted but it didn’t say how much fish oil the men took.
And nor did it reveal the men’s diets, which may have shown they were getting omega-3 from other sources such as fresh fish.
Professor Sheena Lewis, reproductive medicine expert at Queen’s University, Belfast, said: ‘This is a large well-designed study and the association between fish oil intake and improved semen quality is compelling.
‘However, the study focuses on healthy young men; mostly with sperm counts already in the fertile range.
‘There is no evidence from this study that infertile men with low sperm counts benefit from fish oil.’
Dr Frankie Phillips, of the British Dietetic Association, said missing information about the men’s diets did make the study’s results less convincing.
She added: ‘Antioxidants, including vitamin C, selenium and vitamin A, as well as zinc and omega-3 fats all have a role in the production of healthy sperm.
‘There is much focus on the diets of women who are trying to conceive, ensuring that they are in the best possible position to achieve a healthy pregnancy, but diet might also be a factor involved in men’s reproductive health.
‘Omega-3 is present in a both animal and plant derived foods, but oily fish stands out as an excellent source of long chain omega-3, and the UK population currently consume way below the recommended ‘at least one portion of oily fish per week’.
‘So including omega-3 is already part of current dietary recommendations – this study on its own can’t prove that upping omega-3 will itself improve testicular function.’
The research was published in the journal JAMA Network Open, by the American Medical Association.