Regular use of fish oil supplements has been linked to an increased risk of a heart condition or stroke in a UK study of over 400,000 people.
But it also reduced the risk of a heart attack in people with existing heart disease.
The finding adds to growing concerns about the supplements market, which is not held to the same exacting standards as the medical drug industry.
The study analysed data on over 415,000 people ages 40 to 69 participating in the UK Biobank, a longitudinal study of the health of people in the United Kingdom.
The finding adds to growing concerns about the supplements industry, which lacks regulatory oversight
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Nearly one-third of those people, who were followed for an average of 12 years, said they regularly used fish oil supplements.
For people without heart issues, regular use of fish oil supplements was associated with a 13 percent higher risk of developing atrial fibrillation - a heart condition that causes an irregular and often abnormally fast heart rate.
Regular consumption was also linked to a five percent heightened risk of having a stroke, according to the study, published in the journal BMJ Medicine.
Conversely, the new study found that people with existing heart disease at the beginning of the research had a 15 percent lower risk of progressing from atrial fibrillation to a heart attack and a nine percent lower risk of progressing from heart failure to death when they regularly used fish oil.
The risk to benefit ratio was influenced by a range of factors. For example, the risk of healthy patients going on to have a heart attack, stroke or heart failure was six percent higher in women and six percent higher in non-smokers.
There was also a greater beneficial effect for older people and men with existing heart conditions, where the risk of transition from good health to death was 11 percent and seven percent lower respectively.
This was an observational study, so no causation could be be established, the authors note.
Should you avoid fish oil supplements?
Fish oil supplements are a good source of omega-3 - essential fats that cannot be made by the body so need to be obtained from your diet
However, supplement use is generally not recommended as it seems any benefits of fish oils comes from eating the fish rather than in supplement form.
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Any benefits of fish oils comes from eating the fish rather than in supplement form
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Omega-3 fats are found in oily fish such as mackerel, kippers, herring, trout, sardines, salmon and fresh tuna.
It is the essential fatty acids eicosapentaenoic acid (EPA) and docosahexaneoic acid (DHA) found in these fish that are healthy for the heart.
Tracy Parker, a senior dietitian at the British Heart Foundation, shared this view: “This research shouldn’t be concerning to people who regularly take fish oil supplements, but it’s also not a green light to start taking them to prevent heart and circulatory diseases.
“In the UK, Nice guidelines don’t recommend taking fish oil supplements to either prevent heart and circulatory diseases or stop another heart attack. Supplements such as omega-3 fatty acids are no substitute for a healthy diet and, instead of focusing on individual nutrients, it’s important to look at your diet as a whole to help lower your risk.
“The traditional Mediterranean diet has been shown time and again to reduce the risk of heart attack or stroke. This includes more fish – white and oily – and less red meat, along with plenty of fruit and vegetables, beans, lentils, nuts, seeds and wholegrains.”
