Male infertility is a growing problem across the globe.

And it’s one that dashes the parental desires of millions of disappointed couples.

Worldwide, 8% to 15% of couples suffer from infertility, and male sexual dysfunctions account for about half the problem.

Those male dysfunctions include low sperm count, abnormal sperm shape, barriers to the delivery of sperm, impaired sexual function, and/or poor sperm motility (i.e., difficulty “swimming” to the egg).

Because the omega-3 fatty acid called DHA is critical to the health of sperm, scientists have explored the potential reproductive benefit of diets rich in fish oil and/or seafood, which are its only good dietary sources: see “Why seafood and fish oil matter to the health of sperm”, below.

We’ve covered promising past research on seafood, omega-3s, and reproduction, most recently in Foster Romance and Fertility with Fish & Fruit?, which provides links to related reports.

The year-long study we summarized in that report found that — compared with couples who ate seafood less than once per month — couples who ate seafood more than eight times per month displayed two distinctions:

  • They engaged in sexual intercourse 22% more often.
  • More of the women became pregnant within a year — 92% versus 79%.

And the time to pregnancy was shortest among the couples in which both the man and woman ate seafood eight times or more per month, versus couples in which only the man ate seafood that frequently.

Now, the results of a joint American-Danish study suggest that fish oil improves the health of sperm and may therefore enhance a man’s ability to fertilize his partner’s eggs.

American-Danish study finds fish oil may boost male fertility
The new study was conducted by scientists from two Danish universities, the Harvard School of Public Health, and Harvard-affiliated Brigham and Women's Hospital in Boston.

As the authors wrote in the introduction to this study, “Many young men have poor semen quality, and the causes are often unknown.” (Jensen TK et al. 2020)

They went on to note that omega-3 fish oil supplements have been found to improve semen quality in men with infertility, but we haven’t known whether they do the same for all men.

For their study, the international team recruited 1,679 Danish men who were undergoing medical examinations to judge their fitness for Denmark’s compulsory military service.

All the men — whose average age was 19 years — completed detailed questionnaires about their diets and use of supplements over the past three months. Out of the total, 98 reported taking fish oil during at least 60 of the past 90 days.

Encouragingly — versus those who took no fish oil — the young men who reported taking fish oil supplements routinely displayed five fertility-related advantages:

  1. Larger testicles
  2. Higher sperm counts
  3. Greater volumes of semen
  4. Higher proportions of normal sperm cells
  5. Lower levels of follicle-stimulating and luteinizing hormone, indicating healthier testicle function

Reinforcing the credibility of their findings, the researchers found a “dose-response” effect of fish oil: versus men who took fish oil less often, those who took fish oil on more than 60 out of the past 90 days displayed superior testicle function.

Importantly, the researchers adjusted their results to account for the known fertility effects of age, alcohol intake, smoking, sexually transmitted diseases, diet, and other factors.

And only fish oil produced these positive effects — the researchers detected no fertility-related benefits among the men who routinely took supplements other than fish oil, including vitamin C, vitamin D, and multivitamins.

Strengths and limitations of the study
Observational (epidemiological) studies like this cannot prove a cause-effect relationship between a food or nutrient and a health condition.

In part, that’s because — compared with other study participants — the men who reported taking fish oil routinely may have been following generally healthier lifestyles.

In addition — unlike in a controlled clinical trial — the researchers couldn’t be sure of the frequency with which the men took omega-3 fish oil. Nor was there certainty about their routine doses of supplemental omega-3s, because fish oil supplements vary in potency.

Accordingly, the researchers noted the need for controlled clinical trials to confirm their findings in a scientifically convincing fashion.

Further, while the men who reported taking fish oil displayed several fertility-related benefits, the researchers couldn’t confidently quantify the significance of those advantages to reproductive success.

Nonetheless, the findings reported by the American-Danish team echo the findings of many animal studies, and those of most prior human studies, including the few relevant clinical trials.

And as the researchers wrote, “… because [compared with the diets our ancient ancestors ate during their evolution into modern people] modern Western diets contain drastically reduced proportions of omega-3sthe present study would add to the substantial evidence suggesting that a return to such diets can have numerous health-beneficial effects, and those may include reproductive effects.”

Why seafood and fish oil matter to the health of sperm
As we said at the outset, omega-3 DHA is critical to the health of sperm, and the only good dietary sources are fish oil and/or seafood.

The body can make very small amounts of DHA — typically, just enough to enable basic brain, vision, immune, and reproductive (sperm health) functions — from the plant-source omega-3 called ALA.

Relatively few plant foods — such as walnuts, avocados, dark leafy greens — contain omega-3 ALA, with flax, chia, and hemp seed being the only rich and widely available sources.

Flaxseed and canola oils contain larger amounts of ALA than any whole plant foods do. However, the body makes very little omega-3 DHA from ALA.

Last but not least, the standard American diet features extremely high, historically unprecedented intakes of the short-chain omega-6 fatty acid called LA, which predominates in most nuts, seeds, and vegetable oils — and that excess greatly reduces the body’s ability to convert dietary omega-3 ALA into DHA.


  • González-Ravina C, Aguirre-Lipperheide M, Pinto F, Martín-Lozano D, Fernández-Sánchez M, Blasco V, Santamaría-López E, Candenas L. Effect of dietary supplementation with a highly pure and concentrated docosahexaenoic acid (DHA) supplement on human sperm function. Reprod Biol. 2018 Sep;18(3):282-288. doi: 10.1016/j.repbio.2018.06.002. Epub 2018 Jun 20.
  • Jensen TK, Priskorn L, Holmboe SA, Nassan FL, Andersson AM, Dalgård C, Petersen JH, Chavarro JE, Jørgensen N. Associations of Fish Oil Supplement Use With Testicular Function in Young Men. JAMA Netw Open. 2020 Jan 3;3(1):e1919462. doi: 10.1001/jamanetworkopen.2019.19462.
  • Martínez-Soto JC, Domingo JC, Cordobilla B, Nicolás M, Fernández L, Albero P, Gadea J, Landeras J. Dietary supplementation with docosahexaenoic acid (DHA) improves seminal antioxidant status and decreases sperm DNA fragmentation. Syst Biol Reprod Med. 2016 Dec;62(6):387-395. Epub 2016 Oct 28.
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