Do vitamins prevent cancer and heart disease?

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In a cohort of nearly 700,000 people, scientists are taking a closer look at whether vitamins help prevent cancer and heart disease.

The vitamins are already taken by more than half of adults in the United States and are still growing in popularity. In the United States alone, around $50 billion was spent on dietary supplements in 2021, and that is expected to nearly double over the next decade or so.

This is not surprising considering the promising health benefits supplements are said to provide, such as disease prevention and overall health improvement. “Many people in this country […] take at least one dietary supplement on a regular basis. If you ask them why, they answer ‘to maintain or improve their general health,’” said John Wong, a member of the United States Preventive Service Task Force (USPSTF).

Since cardiovascular diseases and cancer are the two main causes of death in developed countries, preventive measures are attractive to maintain a long and healthy life. With the amount of money spent each year, one would hope that there would be some degree of certainty about the benefits of supplements. However, the science is still unclear, with many studies providing mixed results.

In a recent study published in the Journal of the American Medical Association By a team led by Elizabeth O’Connor, associate director of the Center for Health Research in Portland, scientists took a closer look at the effect of supplements on preventing cancer and heart disease.

“One of the most difficult issues with supplements is that we in our daily diets have foods that are sometimes supplemented […] or foods we have that naturally provide vitamins, minerals and nutrients,” Wong said. Take, for example, vitamin D, whose daily levels are determined by both diet and sun exposure. Vitamins and other supplements are also added to processed foods, such as vitamin C, which acts as a preservative.

So how can researchers accurately measure vitamin intake compared to a control group if supplements aren’t the only source? Not to mention the variability in individual metabolism, varying diets and lifestyles.

In general, the answer lies in analyzing larger groups of people, as large datasets translate to greater confidence in the statistical analysis performed – the more information we have, the more accurate our estimates can be and the lower the uncertainty caused by anomalies.

To help provide a clearer answer, O’Connor and his team reviewed 84 studies, which included more than 700,000 healthy participants and excluded children, those with chronic conditions and pregnant women.

The results are in…

The team found that multivitamins had a small overall positive effect on reducing cancer risk, 8.0% compared to 7.5% in women over 60. Effects were negligible in other population groups, and similar results were found for cardiovascular disease.

The analysis also found that in 94,830 people who regularly took beta-carotene – a precursor to vitamin A – this supplement increased the risk of lung cancer by 20% in people who were already at high risk due to smoking or environmental exposure to substances such as asbestos. Additionally, in a study group of 2,297 people, vitamin A was found to increase the overall risk of mortality by 17% compared to the control group. The researchers wrote that the explanation for this result, as well as the increased risk of lung cancer, is still unclear and recommend further study in a larger cohort.

The researchers also determined that there is no clear evidence of the beneficial effects of vitamin D and calcium in the prevention of cancer or cardiovascular disease. Evidence also suggests that vitamin D increases the risk of kidney stones in women.

Overall, the results of this analysis indicate that vitamin supplements may have a beneficial impact on health, but the effect is small. Adopting a healthier lifestyle, which includes both healthy eating and regular physical activity, will have greater long-term benefits, according to Wong.

This study and a statement issued by the task force based on these findings will help shed light on these outstanding questions and have also highlighted the gaps that still exist in this area of ​​research.

The hope is that in the future, studies will become standardized and optimized to better define the potential benefits and risks associated with taking vitamins and supplements daily. Until then, perhaps we should be wary of health quick fixes.

Reference: Elizabeth A. O’Connor, et al., Vitamin and mineral supplements for primary prevention, Journal of the American Medical Association (2022). DO I: 10.1001/jama.2021.15650

Image credit: Diana Polekhina on Unsplash

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