Taking multivitamins regularly is not linked to a lower risk of dying, new research suggests.
The new study found that healthy adults who took daily multivitamins did not have a lower risk of dying over the course of the study, compared to who did not take any.
There were also no differences in rates of death from cancer, heart disease, or conditions that affect blood flow to the brain.
People across the world take supplements with the hope of improving their health, but benefits and harms of regular multivitamin use remain unclear.
In the initial years of the study, the researchers actually found that the risk of death was 4% higher among multivitamin users, compared with nonusers.
They suggested that some vitamins in the supplements may have an impact on other drugs being taken, for example vitamin K may reduce the efficacy of the anticoagulant warfarin.
Some experts suggest that shifting the focus from supplements to food may provide benefits that vitamins cannot deliver.
For the study, researchers at the National Institutes of Health’s National Cancer Institute USA, analysed data from nearly 400,000 healthy American adults who were followed for more than 20 years.
However, they say it is important to also study the potential impact of regular multivitamin use on other health conditions associated with ageing.
Writing in the journal Jama Network Open, the study authors said: “In this cohort study of 390,124 US adults without a history of major chronic diseases, we did not find evidence to support improved longevity among healthy adults who regularly take multivitamins.
“However, we cannot preclude the possibility that daily multivitamin use may be associated with other health outcomes related to ageing.”
Writing in a linked commentary, Neal Barnard, Hana Kahleova and Roxanne Becker, of the Physicians Committee for Responsible Medicine, Washington, said: “Refocusing nutrition interventions on food, rather than supplements, may provide the mortality benefits that multivitamins cannot deliver.
“Vegetables, fruits, legumes and cereal grains are staples in areas of remarkable longevity, known as Blue Zones—Okinawa, Japan; Sardinia, Italy; the Nicoya Peninsula, Costa Rica; the island of Ikaria, Greece; and Loma Linda, California.”
And the inclusion of iron in a supplement adds to that in foods, increasing the risk of iron overload, which is associated with an increased risk of heart disease, diabetes, and dementia, the commentary continued.
The experts also said similar concerns may apply to copper supplementation, and calcium and zinc may reduce the absorption of certain antibiotics.
