A person pours a fish oil pill into their hand.
Given that human sperm quality has declined steadily for the past 50 years, supplements that could improve outcomes are certainly worth another look. (For Spectrum Health Beat)

Couples struggling to get pregnant might want to add a little more fish in their diet, a new study says.

Young men who take fish oil supplements appear to have better sperm quality and higher testosterone levels than those who don’t, as well as larger testicles, researchers report.

Although it wasn’t tested as part of the study, all these male reproductive factors should lead to overall improved fertility in young men taking fish oil, said lead researcher Tina Kold Jensen, a professor of environmental medicine at the University of Southern Denmark.

“Because they have a better sperm count, as a group they would have a better chance of fertilizing an egg,” Jensen said.

Fertility supplements haven’t always had a great track record.

For example, supplements containing zinc and folic acid don’t appear to boost male fertility despite their reputation, according to a study published this month in the Journal of the American Medical Association.

And this latest study can’t prove a direct cause-and effect link between fish oil and the improvements in sperm counts and testosterone levels, much less an improvement in overall fertility, noted Albert Salas-Huetos, a postdoctoral researcher of male infertility at the University of Utah School of Medicine in Salt Lake City.

“With one observational study, it’s impossible to recommend fish oil to a general population,” said Salas-Huetos, who wrote an editorial accompanying the study. “Well-designed randomized clinical trials are necessary to establish a causal relationship.”

The study and editorial were published recently in the journal JAMA Network Open.

But there’s reason in the data to believe that the omega-3 fatty acids in fish oil had a direct effect on sperm count and testosterone levels, Jensen argued.

Sperm cells contain a lot of omega-3 fatty acid, so it would make sense that increasing your intake would lead to healthier sperm, Jensen said.

The study involved nearly 1,700 young Danish men who reported for a compulsory medical examination between 2012 and 2017 to determine their fitness to serve in the military.

“They were healthy 18- or 19-year-old men with no diseases and no knowledge of their fertility,” Jensen said. The researchers offered the men $74 to complete an additional questionnaire and provide semen and blood samples.

About 6% of the men reported using fish oil supplements within the past three months, and half of those said they’d taken them 60 or more days during that period, researchers said.

These men had significantly higher semen volume and total sperm count, researchers found.

Interestingly, the study found no significant difference in sperm quality when they looked at men taking other sorts of daily supplements, Jensen said.

“The men who took multivitamins or B vitamins or C vitamin didn’t have the same effect,” Jensen said. “To me, that points to the fact that it could be the fish oil and not just the healthiness of the men or their healthier lifestyle.”

Jensen added that she would expect to see the same effect in older men taking fish oil supplements.

Two previous clinical trials found that older men had better sperm counts after 14 weeks of eating nuts as a means of improving their omega-3 intake, Jensen said.

Jensen said she would definitely recommend taking fish oil supplements to try and improve male fertility.

“It would be even better to eat more fish, to make sure you have a healthy diet with a lot of fish included,” Jensen said.

While he stopped short of a recommendation, Salas-Huetos said the new study is an important step in figuring out the factors that influence male fertility.

“As you know, human sperm quality has declined worldwide in the last 50 years,” Salas-Huetos said. “It’s really important to find the factors that are associated with human semen decline.”

Pollution, smoking, alcohol, lack of physical activity, stress and unhealthy diets have been associated with a decline in semen quality, Salas-Huetos said.