Study suggests Vitamin D and fish oil supplements may help prevent autoimmune disease

Taking daily vitamin D and fish oil supplements may help protect older adults from developing autoimmune disorders such as rheumatoid arthritis, psoriasis, thyroid diseases and polymyalgia rheumatica, an inflammatory disease that causes muscle pain and stiffness in the shoulders and hips, a new study found.

This article is a repost which originally appeared on CNN
Sandee LaMotte - January 27, 2022
Edited for content and readability - Images sourced from Pexels 
Source: doi: https://doi.org/10.1136/bmj-2021-066452

Our Takeaways:

  • The body makes vitamin D when the skin is exposed to sunshine, and consuming fortified food and beverages.
  • People (aged 50+) taking 2,000 IU of vitamin D3 for over five years had a 22% lower rate of confirmed autoimmune diagnoses.
  • Taking both vitamin D and omega-3 fatty acid supplements, versus the placebo, decreased autoimmune disease by about 30%.
  • You should always talk to your doctor first before starting a new regimen.

People age 50 and older taking 2,000 IU (International Units) of vitamin D3 for over five years had a 22% lower relative rate of confirmed autoimmune diagnoses, said study author Dr. Karen Costenbader, a professor of medicine at Harvard Medical School in the division of Rheumatology, Inflammation and Immunity and the director of the lupus program at Brigham and Women’s Hospital in Boston.

That dosage is two to three times the recommended daily dose of vitamin D for adults, which is 600 IU for people up to 69 years old and 800 IU for those age 70 and up, according to the National Institutes of Health.

Once people had been taking vitamin D for at least two years, the prevention rate from autoimmune disorders rose to 39%, according to the study, published Wednesday in the journal BMJ.

The study also found a possible link between taking 1,000 milligrams of omega-3 fatty acid (fish oil) and a reduction in autoimmune disorders, but the association was not statistically significant until possible cases of autoimmune disease — not just confirmed cases — were factored into the analysis.However, the study did find that taking both vitamin D and omega-3 fatty acid supplementsversus the placebo alone, decreased autoimmune disease by about 30%.

Vitamin D toxicity

People should not just run out and start popping vitamin D pills to boost their chances of avoiding autoimmune disease, Costenbader warned, as there are significant consequences to taking too much of the supplement.

Unlike water-soluble vitamins, which the body can easily eliminate, vitamin D is stored in the fat cells of the body and can build up to toxic levels, leading to bone pain and kidney damage.Because the body makes vitamin D when the skin is exposed to sunshine, and milk and other foods like cereals are often fortified with vitamin D, many experts say healthy, younger people are not likely to require vitamin D supplements, especially in amounts over the recommended level of 600 IU/day.

Levels do drop in older age, but “I would say everybody should talk to their doctor first before taking 2000 international units of vitamin D on top of whatever else you’re taking,” Costenbader said. “And there are certain health problems such as kidney stones and hyperparathyroidism (a rise in calcium levels), where you really shouldn’t be taking extra vitamin D.”

The body attacks itself

Costenbader’s study analyzed 25,871 men and women age 50 and older who were participating in VITAL, a randomized, double-blind, placebo-controlled research study designed to see whether taking daily dietary supplements of vitamin D3 (2000 IU) or omega-3 fatty acids (1,000 mg of Omacor fish oil) would reduce the risk for developing cancer, heart disease and stroke in people with no prior history of these illnesses.That trial showed no benefits from the extra supplementation in preventing either cardiovascular disease or cancer. Because prior research has shown both vitamin D and omega-3 fatty acids derived from seafood can have a positive effect on inflammation and immunity in autoimmune disorders, Costenbader decided to use the same trial to investigate whether the supplements might prevent such diseases.

Autoimmune disease occurs when the body’s natural defense system suddenly sees normal cells as invaders and begins destroying those cells by mistake. In rheumatoid arthritis, for example, the immune system attacks the lining of joints, creating inflammation, swelling and pain. With psoriasis, overactive T-cells — which are among the body’s best defenders — cause inflammation that creates raised, scaly patches on the skin.In Type 1 diabetes, the body’s defenders destroy the insulin-producing cells of the pancreas. There’s even some evidence to show that inflammation throughout the body might be part of the progression of Type 2 diabetes. Autoimmune disorders can develop at any stage of life but do appear more among older adults, particularly women, Costenbader said.

More research needed

To date, no large randomized clinical trials (considered the gold standard of research) had investigated whether fish oil and vitamin D could actually prevent the development of autoimmune diseases.

“This is the first direct evidence in older adults that taking vitamin D or omega-3 fatty acids — or a combination — for five years reduces autoimmune disease incidence, with more pronounced effect after two years of supplementation,” Costenbader said.At five years into the research, the study could not tease apart which of the 80 or more autoimmune diseases might benefit most from vitamin D and fish oil supplements, Costenbader said, but research is continuing. The study is now in its seventh year, she said. and more data should be released in the future.

Is fish oil beneficial for men?

What to know about the benefits of fish oil for men

Medically reviewed by Grant Tinsley, PhD — Written by Zia Sherrell, MPH on March 7, 2021

This article is a repost which originally appeared on MEDICALNEWSTODAY

Edited for content

Fish oil is a common dietary supplement rich in omega-3 fatty acids. Research suggests they could be beneficial for health and protection from certain diseases. Additionally, there may also be specific benefits for men, as fish oil might help with erections and fertility.

People who eat lots of oily fish may get enough of these fatty acids from their diet. For those who do not, or only occasionally, eat fish, taking a fish oil supplement could ensure they get sufficient amounts.

This article explores the potential benefits of fish oil for men and the possible risks. It also suggests how people may increase their levels of omega-3.

Definition of fish oils

Fish oil comes from various species of oily fish, such as mackerel, tuna, and herring. Manufacturers can use many different methods to harvest fish oil, but most techniques typically involve a four-stage process that includes cooking, pressing, filtering, and centrifuging the resultant oil.

Fish oils contain omega-3 polyunsaturated fatty acids. These are essential fatty acids that the body cannot make itself. Two of the most well-known types of omega-3 are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Consuming fish oils and omega-3 may bring some health benefits and help with a number of health conditions.

List of possible benefits

Fish oil may have an impact on different areas of health and be a useful supplement for many people. The following is a list of some potential benefits of fish oil for men.

Sexual health and fertility

Although not widely reported, fish oil supplements may have benefits for sexual health and fertility.

A 2017 animal study examined the effects of omega-3 fatty acids and erectile dysfunction due to atherosclerosis. In this condition, the blood vessels narrow, which can affect erections. Rats in the treatment group fed omega-3 fatty acids demonstrated significantly improved erection quality.

It is essential to bear in mind that animal studies do not indicate the same results in humans. However, an earlier review also indicates that omega-3 could help men with erectile function.

In a 2020 study of 1,694 young male participants, those who reported using fish oil supplements had larger testes and higher semen volume and quality.

They also had a healthier-looking profile of follicle-stimulating hormone and luteinizing hormone. These are two key hormones that regulate sperm production.

Although the study cannot conclude that the fish oil is causing the improvement, it suggests that it may play a role.

Mental health

Research suggests that individuals with depression may have lower blood levels of omega-3 fatty acids. In a small study of 23 people published in Psychiatry Research, supplementation with omega-3s helped improve symptoms of depression within 3 weeks.

There are links between depression and memory problems. Supplementing with DHA alone or in combination with EPA may improve memory function in some groups of adults.

While studies suggest that omega-3 supplementation may help prevent cognitive decline, especially in older adults, a 2019 review notes that more research is still necessary.

Heart health

Heart disease accounts for 1 in 4 deaths in the United States each year. According to the Centers for Disease Control and Prevention (CDC), heart disease is the leading cause of death for men in the U.S.

Eating fish may have a protective effect on heart health by reducing some of the risk factors for heart disease.

Triglycerides are a type of fat found in the blood, and although the body needs them, if levels are too high, they can increase the risk of heart disease.

Fish oil may help lower elevated triglyceride levels and blood pressure. Eating fish may also help to significantly lower low-density lipoprotein or “bad” cholesterol.

While many sources promote the potential benefits of fish oil for cardiovascular health, clinical studies do not consistently support them. For example, an analysis published in JAMA Cardiology could not find a clear link between fish oil and lower heart disease risk.

Eye health

Some evidence suggests that an adequate intake of fish oil may help protect eye health. A 2017 review notes that fish oil may play a role in the treatment of inflammatory eye diseases such as age-related macular degeneration (AMD) and dry eye disease.

A 2019 study indicates that people who regularly consume fresh fruits, vegetables, and fish were less likely to develop AMD compared with those who did not.

The American Academy of Ophthalmology (AAO) recommend fish oils to reduce the symptoms of dry eye. However, some evidence suggests they have no effect. A 2018 study found no evidence to indicate that taking fish oil supplements was more helpful than taking a placebo for dry eye.

Optometrists may recommend taking omega-3 supplements or increasing dietary fish consumption to benefit eye health, even though some scientific evidence suggests fish oils are not suitable for this purpose.

Risks and considerations

Before deciding to supplement their diets with fish oils, people should also consider the possible risks.

While some research indicates that eating a diet rich in omega-3 may help prevent prostate cancer, other research suggests otherwise. A 2013 study notes that a high fish oil intake may actually increase the risk of high-grade prostate cancer.

The National Institutes of Health (NIH) note that the link between omega-3 and different types of cancer, such as prostate, currently remains unclear.

Some people may experience mild side effects if they supplement with fish oil. These may include unpleasant taste, bad breath, diarrhea, flatulence, nausea, and other digestive symptoms.

How to increase your omega-3 level

The three primary omega-3 fatty acids are EPA, DHA, and alpha-linolenic acid (ALA). While the first two are present in fish oil, ALA comes from plant oils such as flaxseed, soybean, and canola oils.

ALA is an essential fatty acid, meaning that the body cannot make it, and it must come from a dietary source. Although the body can convert small amounts of ALA into EPA and then to DHA, the most practical way to increase these omega-3 fatty acids is from food or a nutritional supplement.

ALA is the only omega-3 that is essential, so it is the only one with a recommended adequate intake. Research suggests that males should aim for roughly 1.6 grams.

Both EPA and DHA do not have official recommended daily dosages as they are not essential nutrients. However, the British Dietetic Association suggest a daily dose of about 450 mg EPA and DHA for adults.

It can be difficult to judge the intake from nutritional supplements, as the amounts of fish oil may vary. For example, 1,000 mg of fish oil from one brand of supplement may contain less or more EPA and DHA than the same amount of oil from another brand.

People can get enough omega-3 by including the following foods in their diet:

  • fish and seafood, especially sardines, tuna, mackerel, salmon, and herring
  • nuts and seeds such as chia seeds and walnuts
  • plant oils such as flaxseed, soybean, and canola oil
  • fortified foods such as some types of eggs, yogurt, and soy beverages

Alternatively, people may benefit from a fish or vegetarian algae oil supplement to boost levels. Some evidence suggests that taking a fish oil supplement with a meal that contains fat may help to increase absorption.

Summary

Fish oil is rich in omega-3, which is an essential nutrient. Eating a diet containing oily fish, or taking a fish oil supplement, can ensure someone has an adequate amount.

Consuming more fish oil and omega-3 may offer some health benefits for men. This may include increasing fertility and improving heart health. However, men should weigh up the benefits with a potential increased risk of prostate cancer.

Anyone who is considering taking supplements should first check with a healthcare provider to ensure that it is safe.

Medical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

Fertility supplements for men: What they are, how they work, and why to take them

Fertility supplements for men: What they are, how they work, and why to take them

“Randomized, placebo controlled clinical trials basically don’t exist in this area.”

This article is a repost which originally appeared on INVERSE

Edited for content

As sperm counts around the world plummet for as of yet unknown reasons and research indicates that male fertility issues account for 40-50% of infertility cases, many men who are struggling to conceive may wonder if they can do something to improve their chances. And, of course, the world of supplements stands at the ready, offering blends specifically advertised to boost male fertility. But do these products work?

Are there any supplements that you can take to boost your fertility?

There are some widely available nutrients have been investigated scientifically for their potential to boost male fertility, including one more associated with female sexual health than male fertility.

These include:

  • Fish oil/Omega-3s
  • Folic acid — much more associated with women, especially in relation to fertility
  • Zinc
  • Antioxidants

These nutrients can come from your diet, but it is also possible to supplement your intake, too.

Do male fertility supplements work?

Inverse spoke with Charles Muller, the director of the Male Fertility Lab at the University of Washington. He has been studying sperm and fertilization for decades. When asked about male fertility supplements, he did have a story to tell.

He had two patients, one from India and one from China, who came to the Fertility Lab for assessment after struggling to conceive. Both had a condition called cryptozoospermia, wherein their semen had incredibly low sperm counts. This condition makes the possibility of fertilization very low.

Both men were treated with medicinal formulas in their home countries for several months, and upon returning to the lab, their sperm counts were high.

“Now, the question is, is that just sort of a random event? Or did these herbal supplements really help them?” Muller wonders.

He says that while there are studies of the types of male fertility supplements commonly touted in the United States, “randomized, placebo controlled clinical trials basically don’t exist in this area.” These kinds of trials are the ‘gold standard’ for sussing out whether any medication or intervention is truly effective.

He also says male fertility studies are complicated by the fact semen samples are extremely variable across populations, and even when taken from the same individual.

To really establish whether a supplement is capable of positively changing semen quality on the population level, a researcher would have to establish a “normal range” for each evaluated semen parameter for each individual in the study.

“There’s a blood-testes barrier”

Even if, theoretically, you have a condition that could benefit from supplementation, the compounds in the supplements may not be able to get where they need to go, Muller says.

“It’s possible those things don’t have any effect whatsoever, because they’re just getting thrown out by the digestive system, or second, it’s possible they’re never making their way into the testes,” Muller says.

“Bioavailability in the testes is very limited, because very little can get into the testes. There’s a blood-testes barrier.”

These issues notwithstanding, Muller says: “I don’t knock people doing initial trials. I do them too, because you might find out if it is worth looking into further.”

What are the best male fertility supplements, according to science?

Should you take male fertility supplements?

The results from the existing studies are mixed. Here is a synopsis of some of the research:

· Fish oil for men:

A recent study of young, Danish military recruits found that Omega-3 supplementation improved sperm health. Inverse previously reported that 98 of 1,679 men evaluated in the study took fish oil as a supplement and they had higher sperm count, semen volume, and testicle size than those who did not.

Muller says that, while this study is promising, it was “uncontrolled in terms of amount of omega-3 and patient selection” — two major limitations to taking the results at face value. The study authors highlight this issues, too, saying “these findings need confirmation in well-designed randomized clinical trials among unselected men.”

Ultimately, the jury is still out on fish oil supplements for men’s fertility, but these preliminary results are promising.

· Folic acid for male fertility:

Folic acid is often billed as an essential supplement for female fertility and sexual health, but what about male fertility?

A meta-analysis of seven studies found sperm concentrations were higher in men who took folate supplements than those who ingested a placebo. How well sperm swam and whether they were the optimal shape and size were not shown to be correlated with folate supplementation.

The study authors concluded: “these results should be interpreted with caution due to the important heterogeneity of the studies included in this meta-analysis. Further trials are still needed to confirm the current findings.”

Inverse also recently covered a large male fertility study which followed 2,300 male partners from couples planning to undergo infertility treatment. The men were divided in half and one group of 1,150 took 30 milligrams of elemental zinc and 5 milligrams of folic acid daily, while the other group took a placebo. After 6 months, both groups had similar birth rates. The researchers concluded, “these findings do not support the use of folic acid and zinc supplementation by male partners for the treatment of infertility.”

· Zinc for men:

Both studies above involve zinc supplementation along with folic acid. Zinc is one of the most popular ingredients in dietary supplements for male fertility, according to a 2020 paper in the journal Nutrients. Overall, it appears to be in some 70 percent of the tested supplements.

Some scientists argue zinc is an essential nutrient for safeguarding male fertility and reproductive health. But as the 2020 paper above argues, the standards for testing how well any one supplement are lacking. And for zinc, the lack of standards can be worrying.

As the authors write in the Nutrients review: “We were surprised to point out that all RCTs and meta-analyses on zinc for male infertility relied on doses always exceeding the UL.”

In other words, many of the tests for zinc supplementation they looked at had doses of zinc which were above the upper recommended intake. Too much zinc can have adverse side affects, they write, sounding a note of caution over this supplement’s supposed benefits.

· Antioxidants:

Antioxidants benefit the body by neutralizing free radicals — metabolic waste products which can wreak havoc on cellular health if not properly disposed of. Free radicals can kill sperm and they can also result in the fragmentation of sperm DNA, which could potentially lead to the loss of a pregnancy or even childhood cancer, according to Muller.

Because of this, antioxidant supplementation has and is being investigated as a way to boost sperm health. One 2016 meta-analysis of four clinical trials found a combination of antioxidant supplements including vitamin C, vitamin E, and CoQ10, “can effectively improve semen parameters in infertile men.”

A clinical study in which participants took a daily antioxidant formulation comprised of vitamin C, vitamin E, selenium, l-carnitine, zinc, folic acid, and lycopene for three to six months found otherwise, however. This study found no benefits for sperm DNA integrity or other semen parameters.

Additionally, some researchers express concern excess antioxidant use could damage fertility through a different process than the damage caused by free radicals. Because of this potential, the researchers write, “we feel that there is a need for more elaborate research to establish the clear benefits and risks involved in antioxidant therapy for male infertility.”

How do you know you need male fertility supplements?

The science is still out on whether these supplements work.

But according to the Mayo Clinic, infertility is a common problem, affecting one in seven couples. They define infertility as the inability to conceive after a year or more of frequent, unprotected sex.

According to the Mayo Clinic, the following factors are crucial for fertilization to be successful:

  • Your sperm must be healthy
  • There needs to be enough of them: Low sperm count decreases the probability of fertilization
  • They need to be effectively transported out of your body: There are a series of delicate tubes and organs involved in the creation, maintenance, and transport of sperm and semen
  • They must be able to move: Sperm motility is a major issue. If they are not moving correctly, they may not be able to travel to the egg cell

These attributes of successful fertilization can be disrupted by factors such as:

  • Infection
  • Retrograde ejaculation (semen enters the bladder during orgasm instead of exiting the body)
  • Auto-immunity conditions
  • Previous surgeries
  • Undescended testicles
  • Hormone imbalances
  • Cancer
  • Chromosomal abnormalities (such as possessing an extra X chromosome)
  • Medications including: SSRI’s, channel blockers, and certain antibiotics
  • Physiological abnormalities in the reproductive tract that prevent the transport of semen or sperm
  • Celiac disease
  • Varicocele (swelling of veins in the testicle)
  • Cystic fibrosis or possessing one of the of the genes that causes cystic fibrosis

While many of these issues can be medically addressed, there are causes of male infertility, such as missing parts of the reproductive tract, that are hard to imagine being effectively treated with supplements.

Can you get the nutrients in male fertility supplements from your diet?

Diet can impact male fertility

Whether or not they work as supplements, omega-3s, folic acid, zinc, and many antioxidants can come from dietary sources.

Additionally, a recent study found correlations between diet and sperm count, and established a kind of diet hierarchy.

Listed from highest to lowest correlated sperm counts, the investigated diets were:

· “Prudent” diet: The researchers described this as a “generally healthy” diet, consisting of fruits, vegetables, fish, and chicken. This bears a lot of similarity to the Mediterranean diet, the benefits of which Inverse has reported on before.

· Vegetarian-like diet: Limited meat and plenty of vegetables, eggs, and dairy.

· Open-sandwich diet: Traditional Danish diet including cold cuts, whole grains, and dairy.

· Western diet: Lots of red meat, fried food, and sugary drinks, and deserts.

Feiby Nassan, a co-author on the study and researcher at the Harvard T.H. Chan School of Public Health, previously told Inverse that “because following a generally-healthy diet pattern is a modifiable behavior, our results suggest the possibility of using dietary intervention as a possible approach to improve sperm quality of men in reproductive age.”

Muller agrees diet is an important factor in sperm health and questions about diet are included on the UW Male Fertility Lab intake form. Specifically, Muller’s team looks out for diets low in omega-3s or high in nitrates.

Ultimately, following a Mediterranean diet may be the best recipe for male fertility health, these data suggest. For more information on the diet’s scientific backing, take a look at these four mental and physical health benefits.

How long do male fertility supplements take to work?

This is a difficult question to answer given the dearth of reliable studies showing they work at all.

However, the Cleveland Clinic website quotes Cleveland Clinic urologist and male fertility specialist, Neel Parekh, as saying that, for men with male oxidative stress infertility (MOSI), which is a condition where there are more free radicals than antioxidants in the semen, “taking supplemental antioxidants for three months or longer can improve sperm parameters. If a patient doesn’t have MOSI, however, taking antioxidants may do more harm than good.”

He also clarifies that this is only the case for men who don’t have other contributing infertility issues.

Muller says it takes about three months for a stem cell to develop into a sperm cell, and so a supplement study should be at least that long.

Some of the studies have found positive effects of supplementation featured trial periods ranging from 8 to 26 weeks.

Testosterone can haunt your sperm

Can male fertility supplements hurt your fertility?

Counterintuitively, testosterone supplementation can reduce sperm count.

According to Muller, while testosterone is necessary for the production of sperm, increasing blood testosterone levels through supplementation (or steroid use) can drive sperm production down because of a negative feedback loop involving the hypothalamus in the brain.

When the hypothalamus detects increased testosterone levels in the blood, it down regulates the production of other important hormones called LH and FSH. When the testes start getting less LH, they reduce their own testosterone production. This is significant because healthy testosterone levels in the testes should be ten times what they are in the blood stream.

“If the testes itself is not making testosterone, it’s going to have the same level as in the blood, which is a 10th of what it needs to stimulate sperm production,” Muller says.

Other lifestyle factors known to potentially reduce fertility are:

· Frequent hot tub/sauna use

· Marijuana use

· Diet low in omega-3s

· Exposure to industrial or environmental toxins at work or in the home including: plasticizers, xylene, toluene

The Inverse analysis — While there is reason to believe that certain kinds of supplementation or traditional herbal formulas could be helpful, that certainly doesn’t mean that anything advertised as boosting male fertility is efficacious or safe.

Fertility can be impacted by myriad factors such as overall health, habits, and environmental stressors which may need to be resolved. If you’re having trouble conceiving, a first step is to get to a specialist and get some analysis done before you start popping pills.

Fish oil can boost sperm count and make men’s testicles BIGGER, study claims

Fish oil can boost sperm count and make men’s testicles BIGGER, study claims

  • Scientists in Denmark tested the sperm and testicles of young, healthy men
  • Supplement-takers had bigger testicles and ejaculated more sperm, on average
  • Research only observed the link and could not prove supplements caused this
  • Experts say omega-3 could be a part of general good health, which is beneficial

By Sam Blanchard Senior Health Reporter For Mailonline
Published: 11:00 EDT, 17 January 2020 | Updated: 15:06 EDT, 17 January 2020

This article is a repost which originally appeared on MAILONLINE

Edited for content

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.

Fish oil supplements contain omega-3 fatty acids, which are believed to reduce the risks of heart disease and improve brain health.

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 39 million 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 147 million for men with no supplement intake, 159 million for men with other supplement intake, 168 million for men with fish oil supplement intake on fewer than 60 days, and 184 million 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.