A study by US researchers of the health records of 400,000 healthy adults shows “no evidence” that a daily multivitamin helps people to live longer.

The researchers behind the study say their findings raise questions about the effectiveness of micronutrients in supplement form, and urge the prioritisation of healthy eating.  

The US team say they wanted to test the effectiveness of multivitamin use in disease prevention, the “primary motivation” for taking them. So they designed a study pooling data from three large-scale trials to see whether daily multivitamins reduced people’s risk of death over the next two decades. Significantly, the study accounted for confounding by healthy lifestyle (supplement users often report eating a healthier diet, exercising more and smoking less, potentially skewing findings) and reverse causation where people in poor health initiate supplement use.

The study showed that rather than living longer, people who consumed daily multivitamins were marginally (+4 %) more likely than non-users to die in the study period, leading the researchers to comment that “multivitamin use to improve longevity is not supported”.

The researchers acknowldge there are potential benefits in supplementation that their study does not capture. As well as suplementing for particular life stages and defiencies (they note many people “come up short” for vitamins B12 and D), they cite the role of beta carotene, vitamins C and E, and zinc in slowing the progression of age-related macular degeneration, and multivamin use to improve memory and cogntive decline in older people. The researchers also point to “important” documented health risks associated with supplementation for particular groups. 

Refocusing on food
In a commentary accompanying their study, the researchers – led by Neal Barnard – stress that “micronutrients come most healthfully from food sources”. They write: “Refocusing nutrition interventions on food, rather than supplements, may provide the mortality benefits that multivitamins cannot deliver … A healthful dietary pattern delivers micronutrients while also providing healthful macronutrients and fibre and limiting consumption of saturated fat and cholesterol.”

Barnard told The Guardian: “Multivitamins overpromise and underdeliver. The main point is that the multivitamins are not helping.” 

Industry reaction
US industry groups say the new study has limited value and misses the bigger picture. The Council for Responsible nutrition (CRN) says that “substantial parts of the (US) population … fall short in (a range of) nutrients of public health concern”. 

Andrea Wong, CRN’s SVP, Science and Regulatory Affairs, said. “There is substantial evidence supporting the role of multivitamins in addressing nutritional needs, reducing the risk of specific diseases and health conditions, and supporting overall health. Analyzing mortality rates in isolation fails to recognize the range of health benefits of multivitamin use identified in rigorous scientific studies, including the reduction of birth defects, reducing cancer risk, slowing cognitive decline, and many others.”

Daniel Fabricant, president and CEO of the Natural Products Association, said: “Nearly 80% of Americans use dietary supplements as a way to support their health and wellness. Obviously, there is no magic bullet for mortality, however, diet and exercise are bullet-proof for life-long health goals. Unfortunately, this study peddles more of the same information NPA has spent nearly 90 years fighting.”

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