Research suggests that supplementing omega-3 and vitamin D may bring health benefits – but it all depends on what we buy.

Many people rely on vitamin D supplements but, even though vitamin D is essential for functions such as bone health and supporting the immune system, it’s long been debated whether supplements actually make a di­fference to health.

Recent research, however, indicates that it’s the type of vitamin D that makes all the difference.

This is what scientists from the Universities of Surrey and Brighton found when they compared vitamin D2 and D3 supplements.

For 12 weeks, 335 women consumed fortified foods containing either 15mg of D2; 15mg of D3; or a placebo.

Analysis of the women’s blood found that only D3 stimulated a key part of the immune system that acts as a first line of defence against bacteria and viruses.

Why D3 a­ffects the human body differently is yet to be explained, but one possible explanation may lie in nature.

When exposed to the sun's UV rays, whilst plants naturally produce D2, the human body naturally produces D3 — which may suggest the human body has evolved to better respond to it.

Look for a preparation close to the same doses of both EPA and DHA, with not a lot else

Vitamin D and omega-3

Whilst D3 has been found to stimulate the immune system, combining D3 with omega-3 may prove even more beneficial.

A study (named VITAL), published in The BMJ, reported that taking vitamin D with omega-3 supplements may prevent the onset of autoimmune diseases, such as rheumatoid arthritis, polymyalgia, thyroid disease and psoriasis.

During the study, 25,871 adults in the USA (average age 67), were given, every day for an average of 5.3 years, either: 50mcg of D3; 1g of omega-3; or matched placebos for either.

When taken for five years, vitamin D — with or without omega-3 — was associated with fewer autoimmune disease diagnoses.

The beneficial effect of omega-3 was greater among participants with a family history of autoimmune disease.

The findings were important, the authors said, because supplements were “well-tolerated, non-toxic… and that there are no other known effective therapies to reduce rates of autoimmune diseases”.

Safety and cautions

Whether supplements can be taken without caution is another question; omega-3 has been associated with a slightly increased risk of cancer.

Dr Karen Costenbader, corresponding author of the VITAL study, told Optimum Nutrition:

“Cancer risks are always a concern with any therapy, although the results of the VITAL trial where cancer was the primary endpoint were reassuring.”

Prostate cancer risk, she explained, was not statistically elevated among participants taking omega-3 but the trial continues to follow participants.

“I do think people can safely take omega-3 fatty acid supplements as there are many years of very good safety data,” she said.

There are, however, some cautions. “There is a slight increased risk of bleeding for people taking anti-coagulants,” she said.

“Liver function tests need to be monitored for those with liver disease, and some people may be allergic to them and unable to take them.

“In particular people with fish or seafood allergies should be cautious.”

Even weight may make a di­fference, as a stronger preventative e­ffect was found among participants with a lower body mass index.

This, it was suggested, may be due to vitamin D being stored in body fat and being less ‘bioavailable’ — meaning whether the body can use a nutrient or not.

Off oils vs fresh fish

Also, not all omega-3 supplements are made equal, with more than 10% of common fish oils in the USA reported to be oxidised (rancid).

Dr Ben Albert, a senior research fellow at the University of Auckland, NZ, says it’s a widespread problem.

Albert said the VITAL study was exciting because it was so large as well as being a randomised trial, “which makes the results more reliable”.

However, he noted that VITAL had used prescription grade omega-3.

“A previous study has shown prescription omega-3 supplements may have di­fferences in composition and rancidity compared to over-the-counter fish oils,” he said.

“It’s not clear that people who go out and purchase fish oil will get the same benefit.”

Albert said that globally, when all the evidence from studies was combined, around 20% of fish oils were oxidised above recommended limits at the time they were bought.

“Because there is no regulatory agency checking fish oil packages for oxidation, it is hard for the consumer to choose a supplement with low oxidation,” he said.

It’s not known what the impact of oxidised fish oils might be on human health, but some animal research has suggested it might be dangerous.

What to buy

Both Costenbader and Albert had advice on what to look for when buying supplements. “VITAL used a prescription grade preparation of omega-3 fatty acids: 1 gm of EPA+DHA combined,” said Costenbader.

“Look for a preparation close to the same doses of both EPA and DHA, with not a lot else — some preparations include soybean oil, olive oil, stabilisers, etc.”

Some research on rodents has associated soybean oil with inflammation, obesity and conditions such as diabetes.

She also said to check safety seals, and whether the product was sustainably produced and purified to remove mercury.

“Consumers…should buy small packages and store them in the refrigerator to reduce the rate that they oxidise at home,” said Albert.

“Alternatively, people could consume more oily fish like tuna, salmon, sardines or anchovies.”

It’s food for thought — and unlike with supplements, if fish goes off­ we are extremely unlikely to eat it.

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