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If you’re taking vitamin D and/or fish oil supplements to help guard against cardiovascular disease or cancer, you’re likely wasting your money. That’s according to new findings from a randomized controlled trial – the largest and longest of its kind – published on Nov. 10 in the New England Journal of Medicine.

Previous observational studies, which don’t prove cause and effect, have shown a link between low blood levels of vitamin D and an increased risk of cancer and heart disease.

Observational research has also suggested that people who eat plenty of fish have a lower risk of heart attack and stroke.

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Randomized controlled studies – the gold standard of scientific evidence – conducted in people who have had a heart attack or who are high risk for cardiovascular disease have turned up inconsistent results on the heart benefits of omega-3 supplements.

In healthy people at average risk for cardiovascular disease or cancer, there’s a lack of data from well-controlled studies on whether fish oil or vitamin D supplements are beneficial. Until now.

The VITAL trial

The Vitamin D and omega-3 randomized controlled trial (known as VITAL) tested whether vitamin D3 and/or omega-3 fatty acids reduce the risk of cancer and major cardiovascular events (defined as a composite of heart attack, stroke and death from cardiovascular disease) in healthy men and women.

The trial, which ran for 5.3 years, enrolled 25,871 Americans of various ethnicities who were over the age of 50 and had no previous history of cancer, heart disease or stroke.

Participants were randomly assigned to take either 2000 international units (IU) of vitamin D3 and one gram of omega-3 fatty acids from fish oil, a vitamin D and a placebo pill in lieu of fish oil, or a fish oil supplement and a vitamin D placebo pill.

The findings: Compared to the placebo group, vitamin D supplementation did not lower the risk of cancer (total cancers or breast, prostate or colorectal cancers) or major cardiovascular events.

Likewise, participants taking a daily omega-3 fatty acid supplement did not experience a reduction in cancer or major cardiovascular events compared to the placebo group.

When researchers looked at heart attacks specifically, they found that participants taking the omega-3 supplement had a 28 per cent lower heart attack risk, and a 50 per cent reduced risk of fatal heart attack compared to the placebo group.

Among participants who ate less than 3 to 4 ounces of fish a week, supplementing with fish oil led to a 19 per cent reduction in major cardiovascular events, including a 40 per cent lower risk of heart attack, compared to the placebo group.

People who ate at least two servings of fish a week did not benefit from taking fish oil, perhaps because they were already getting adequate omega-3s by eating fish.

Among African-Americans, taking fish oil led to a 77 per cent reduction in heart attacks, whether these participants were infrequent fish eaters or not.

Keep in mind, though, these secondary findings about heart-attack risk and omega-3 supplements need to be replicated; they haven’t been consistently found across other large randomized controlled trials.

Strengths and limitations

This trial is noteworthy. It included a large sample of racially and ethnically diverse participants, making the findings applicable to most people age 50 and older.

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It showed that 2000 IU of vitamin D had no effect on cancer risk across a wide range of blood vitamin-D levels, including participants who were deficient. Study participants were also highly compliant to their pill regimen.

There were limitations, though. The trial may have been too short in duration to find an effect of vitamin D or omega-3s on cancer risk.

It also didn’t test dose response; it’s not known if a higher dose of the supplements could have led to better results.

What to do?

If you’re already taking a vitamin D and omega-3 supplements in the doses studied, there’s no reason to stop taking them based on the findings. There was no difference in adverse events between the supplement and placebo groups.

If you don’t eat fish often, consider adding it to your diet twice a week before reaching for a supplement. Besides omega-3s, fish delivers protein, vitamin B12, selenium, iodine and potassium.

Fish high in omega-3 fatty acids – EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) – include salmon, trout, Arctic char, sardines, herring and mackerel.

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If you’re unlikely to add more fish to your diet, consider taking an omega-3 supplement. The results, though not conclusive, suggest doing so may reduce the risk of heart attack. DHA supplements made from algae are available for people who follow a vegan diet.

Current vitamin-D intake recommendations are based on maintaining a sufficient vitamin-D blood level for bone health, not cancer or heart disease prevention. Until age 70, adults need 600 IU per day; older adults require 800 IU. (Some people may need more to maintain a sufficient level.)

Additional VITAL studies are testing whether vitamin-D and omega-3 supplements affect the risk of diabetes, cognition, autoimmune diseases, depression and other health outcomes. These results, expected over the next six to 12 months, may provide a more complete picture of the benefits and risks of supplementation.

Leslie Beck, a Toronto-based private practice dietitian, is Director of Food and Nutrition at Medcan.

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