Is a diet low in omega-3 worse than smoking?

23 July 2021

A recent study suggests that low levels of omega-3 fatty acids in the blood can shorten your life as much as smoking.

Omega-3 fatty acids (the type found in oily fish such as salmon, sardines and mackerel) can help to keep your heart healthy, which is why we’re all recommended to eat one portion of oily fish per week. Omega-3 fatty acids are thought to help keep your blood vessels healthy and to help to reduce blood pressure.

The researchers set out to see if fatty acid levels in the blood could predict a person’s risk of early death in the same way as other risk factors associated with heart disease, such as age, sex, smoking and having diabetes. This could help identify people at risk of early death and ensure they get the right treatment to reduce their risk.

The study, published in the American Journal of Clinical Nutrition, followed 2,240 people over the course of 11 years. The researchers took blood samples from participants to measure levels of different fatty acids in the blood.

The researchers found that levels of omega-3 were a useful predictor of life expectancy, and compared well to established risk factors in terms of accuracy.

On average, people with the lowest levels of omega-3 lived 4.7 years less than those with the highest. Smoking had the same impact – 4.7 years of life lost, compared with non-smokers.

The researchers noted that the life expectancy in Japan, where people eat more oily fish and have higher omega-3 levels, is five years longer than in the United States.

The study’s authors conclude that there is “a strong association” between the omega-3 levels and mortality, and that “dietary choices that change omega-3 [levels] may prolong life.”

The study also looked at levels of nine other fatty acids and found three that were linked with life expectancy. People with higher levels of myristic acid and behenic acid were more likely to live longer, while those with higher levels of palmitoleic acid lived for less time. These fatty acids are less directly linked with diet than omega-3s, although the authors suggest that the myristic acid levels could be linked to consuming dairy products, which have been linked to some health benefits.

The researchers said that although they expected to see a link between omega 3 and life expectancy, the other fatty acids were not necessarily the ones they would have expected to show a link. And unlike omega-3, there isn’t a clear link between diet and levels of the other fatty acids in the blood.

They said their research suggests that consuming more omega-3 (as oily fish or in supplements) and not smoking are the biggest changes people can make to increase their life expectancy.

How good was the research?

One strength of the study is that it sampled a large number of people over a long period of time.

A weakness of the study is that it looks at risk of death in an older population, with an average age of 65 at the start of the study, and 76 at the end of the study, so its findings can’t be applied to the entire population. Further studies are needed to see if these results are the same in other age groups. The study compared the accuracy of fatty acids to predict risk of death, with existing measures (such as blood pressure, cholesterol levels, whether you smoke and whether you have diabetes). The researchers point out that the existing measures were developed from research in people with an average age of 49, so they may not be equally accurate in older age groups. Risk factors may affect the life expectancy of an older person differently to a younger person.

It can also be difficult to compare the effect of omega-3 levels with smoking, especially as omega-3 levels can fluctuate. The study measured the levels of omega-3, but did not measure how much people smoked – only whether they smoked or not.

The BHF view

Senior Dietitian Victoria Taylor says “Including fish as part of a healthy balanced diet has been a long-standing recommendation in the UK and it’s also a feature of the Mediterranean diet, which is associated with benefits to heart and circulatory health.

“But on average we are eating far less than the one portion of oily fish a week that’s recommended.

“Salmon, sardines or mackerel are all good options and easy to get hold of – try them in fish cakes, pasta or in a salad.”

How accurate was the media coverage?

The story was covered in the Daily Mail, The Telegraph and the Daily Express.

The Daily Mail says that “lack of omega-3 in the diet can shorten life even more than smoking”. This is not what the research says. The main takeaway of the research is that omega-3 levels could be used to predict risk of death, like smoking can. It found that smoking was linked to the same difference in life length as the lowest levels of omega 3 compared with the highest. The Mail article does helpfully suggest ways that risk can be reduced, including diet, and reducing tobacco and alcohol.

The Telegraph’s coverage has “Diet low in Omega-3 ‘can reduce life expectancy like smoking’”. It’s important to remember that research like this can only show an association, not prove cause and effect.

The Daily Express headline reads “How to live longer: One food you should never skip –you may shorten your life expectancy”. Although the headline is understandably trying to make this research relevant to people’s lives, omega-3 is not a food, and the article doesn’t go on to explain what “never skip” means in practice. The study only looked at blood levels of omega-3, not how much oily fish or supplements you’d need to consume to have the highest omega-3 levels. It does tell us that this is in ‘older adults’ although highlighting the ages of the people involved would be even more useful.

None of the news coverage mentions that the research also found other fatty acids linked with life expectancy, not just omega-3.