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How can vitamin D and fish oil affect your risk of stroke and cancer?

How can vitamin D and fish oil affect your risk of stroke and cancer?Scientists have discussed for quite some time to what extent vitamin D or omega-3 fatty acids from fish oil are able to lower the risk of a heart attack, stroke, and cancer. Although quite a lot of studies have been conducted in this area, there still is no large-scale clinical population study that includes different races. However, an American study has shown that fish oil supplements lower your risk of a heart attack, and large quantities of vitamin D have a long-term preventative effect on different cancer forms. The effect of these two different supplements is also affected by a person’s race.

The new study, which is named VITAL, was headed by scientists from Brigham and Women’s Hospital in Boston, Massachusetts, USA. Twenty-six thousand men and women aged 50 years and older from all parts of the United States participated, and 20 percent of the participants were African-American. VITAL was carried out like a randomized, double-blind, placebo-controlled study that lasted more than five and half years and provided an abundance of information. VITAL is one of the few studies to investigate a diverse population group and look closer at the preventive effect of supplementing with vitamin D and fish oil.

Because VITAL was designed to test the effect of vitamin D and fish oil on a separate basis, the participants were divided in four groups, each of which received one of the following regimens every day:

  1. Vitamin D (50 micrograms) and fish oil (1 gram)
  2. Vitamin D (50 micrograms) and placebo
  3. Fish oil (1 gram) and placebo
  4. Vitamin D placebo and fish oil placebo

Fish oil is particularly effective for preventing heart attacks

The researchers compared the participants that got real fish oil supplements with those that got fish oil placebo. Over a five-year period, they noted a 28% lower (significant) risk of heart attack with 145 cases of stroke in the fish oil group and 200 cases in the placebo group. Among the participants, who had lower consumption of dietary fish, there was an even greater protective effect, as their risk of a heart attack was 40 percent lower. In addition, a greater protective effect was observed among African-American study participants.
The researchers see a huge potential in using fish oil for preventing cardiovascular diseases – especially in population groups that are more exposed.
No significant difference was observed in terms of cancer, which is most likely because the participants only got one gram of fish oil and limited quantities of EPA (eicosapentaenoic acid), which is believed to be able to prevent several cancer forms by inhibiting inflammation.

Did you know that one herring fillet contains a gram of fish oil, while a salmon steak contains three?

Vitamin D prevents cancer – in the long run

The scientists also looked at vitamin D’s impact on cancer rates. After five years, 1,617 study participants had been diagnosed with cancer. Seven hundred-ninety-three of them had taken supplements of vitamin D, and 824 had taken placebo. At that point, there was no significant difference between the two groups. Two years later, however, the researchers noted a significant difference, as cancer mortality had been reduced by 25% in the group that took vitamin D. Because it often takes years for cancer to develop, vitamin D appears to have a greater long-term effect, which means that it is important to get enough of the vitamin through all stages of life.
The participants received 50 micrograms of vitamin D daily, which is an amount that your body can easily synthesize on a summer day with adequate sun exposure. However, dark-skinned individuals and older people, who often have thin skin, do not produce as much vitamin D. Also, overweight individuals and diabetics have difficulty with synthetizing and utilizing the vitamin. In places like Scandinavia and other parts of the world where there is lack of sunshine during the winter period, it may be advisable to take a vitamin D supplement, considering how little of the vitamin we get from our diets.

Other effects of the two supplements and updating of the RI (reference intake) levels

No serious side effects were observed such as bleeding due to the fish oil supplementation or elevated calcium levels due to vitamin D supplementation. Similarly, fish oil and vitamin D did not appear to counteract each other, and they are both present in things like cod liver and cod liver oil. Besides the cardiovascular benefits and the effect on cancer, the scientists plan to look closer at how the two supplements work on diabetes, cognitive functions, autoimmune diseases, respiratory infections, and depression. This is very relevant, as there is already a lot of research in this area.
With regard to the study results so far, the scientists urge health authorities to update the official guidelines for intake of vitamin D and fish oil. There are no official recommendations for omega-3 intake, other than general advice about including fish as part of a healthy diet. Many people do not like fish, however, or they simply don’t eat enough of it. It is therefore a good idea to take a supplement to make sure to get at least one gram of fish oil daily, which is the amount that was used in the study.


Brigham and Women´s Hospital. Study: How vitamin D and fish oil affect risk of heart attack, stroke and cancer. November 2018

Sarawoti Khadge et al. Long-chain omega-3 polyunsaturated fatty acids decrease mammary tumor growth, multiorgan metastasis and enhance survival. November 2018


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