A high intake of alpha linolenic acid (ALA) - found mainly in nuts, seeds and plant oils - is associated with a lower risk of death from all causes, and specifically from diseases of the heart and blood vessels, finds a new study.
A higher ALA intake was associated with a slightly higher risk of death from cancer, but the researchers say further studies are needed to confirm this.
Alpha-linolenic acid (ALA) is an omega-3 polyunsaturated fatty acid found in plants, such as soybeans, walnuts, canola oil, chia seeds, ground flax and hemp seed.
Previous studies have shown that a high ALA intake is associated with a lower risk of fatal coronary heart disease, but findings from other studies on ALA and risk of death have been inconclusive.
About the new research
To address this uncertainty, an international team of researchers analysed the results of 41 studies published between 1991 and 2021 on the associations between ALA intake and risk of death from all causes, cardiovascular disease and cancer.
Together, these studies involved around 120,000 participants between the ages of 18 and 98 years who were followed for up to 32 years. The researchers accounted for other cardiovascular and cancer risk factors such as age, weight, smoking status, alcohol consumption and physical activity.
The resuls showed that a high intake of ALA was associated with a 10%, 8%, and 11% lower risk of mortality from all causes, cardiovascular disease (e.g., heart disease and stroke combined) and coronary heart disease, respectively.
This is equivalent to 113 fewer deaths per 10,000 person years for all causes, 33 fewer cardiovascular disease deaths and 23 fewer coronary heart disease deaths.
A higher intake of ALA, however, was associated with a slightly higher risk of cancer mortality.
A dose-response effect was found for dietary ALA intake and cardiovascular disease mortality, such that a 1 gram per day increase in ALA intake (equivalent to one tablespoon of canola oil, 1.5 teaspoons of ground flax or chia seeds or 6 walnut halves) was associated with a 5% lower risk of cardiovascular disease mortality.
Higher blood levels of ALA were also associated with lower risks of mortality.
Study limitations
Due to the observational design of the reviewed studies, causality cannot be established, nor can the researchers rule out the possibility that other unknown factors or measurement errors of food and nutrient intakes might have affected their results.
Still, the study adds to evidence of the potential health benefits of the plant-based omega-3 fatty acids, ALA.
Despite the beneficial effects of omega 3 fatty acids, it suggests that recommendations for intakes should be made cautiously because ALA intake might slightly increase the risk of cancer mortality. Further studies are, however, needed to confirm the increased risk.
Source: BMJ, October 13, 2021.
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