Taking a daily multivitamin does not help people to live any longer and may actually increase the risk of an early death, according to a major study in which American researchers analysed health records from almost 400 000 adults.
Their aim was to see whether daily multivitamins reduced their risk of death over the next two decades.
However, reports The Guardian, rather than than living longer, people who consumed daily multivitamins – none of whom had any major long-term disease – were marginally more likely than non-users to die in the study period, prompting the government researchers to comment that “multivitamin use to improve longevity is not supported”.
Nearly 50% of all British adults take multi-vitamins or dietary supplements once a week or more, and while the global market is estimated to be worth tens of billions of dollars each year, researchers have questioned the health benefits and even warned that the supplements can be harmful.
While natural food sources of beta-carotene protect against cancer, beta-carotene supplements – for example – can raise the risk of lung cancer and heart disease, suggesting the supplements are missing important ingredients.
Meanwhile iron, which is added to many multivitamins, can lead to iron overload and raise the risk of cardiovascular disease, diabetes and dementia.
For the latest work, Dr Erikka Loftfield and colleagues at the National Cancer Institute in Maryland, USA, analysed data from three major US health studies. All launched in the 1990s and gathered details on participants’ daily multivitamin use. The records covered 390 124 generally healthy adults who were followed for more than 20 years.
The researchers found no evidence that daily multivitamins reduced the risk of death and reported instead a 4% higher mortality risk among users in the initial years of follow-up.
The greater risk of death may reflect the harms multivitamins can cause or a trend for people to start daily multivitamins when they develop a serious illness. The findings were published in JAMA Network.
Dr Neal Barnard, an adjunct professor of medicine at George Washington University and co-author of a commentary published alongside the study, said vitamins were useful in specific cases. Historically, sailors were saved from scurvy by vitamin C, while beta carotene, vitamins C and E, and zinc appear to slow age-related macular degeneration, a condition that can lead to severe loss of eyesight, he said.
Additionally, vitamins may be beneficial without reducing the risk of early death. A preliminary study in 2022 found evidence that multivitamins might slow cognitive decline in old age, but more research was needed.
Yet “multivitamins over-promise and under-deliver”, Barnard said. “The main point is they are not helping. The science is not there.”
Instead of taking multivitamins, people need to eat healthy foods, he added, which provide a broad range of micronutrients, macronutrients and fibre, while limiting saturated fat and cholesterol.
Study details
Multivitamin Use and Mortality Risk in 3 Prospective US Cohorts
Erikka Loftfield, Caitlin O’Connell, Rashmi Sinha et al.
Published in JAMA Network on 26 June 2024
Abstract
Importance
One in 3 US adults uses multivitamins (MV), with a primary motivation being disease prevention. In 2022, the US Preventive Services Task Force reviewed data on MV supplementation and mortality from randomised clinical trials and found insufficient evidence for determining benefits or harms owing, in part, to limited follow-up time and external validity.
Objective
To estimate the association of MV use with mortality risk, accounting for confounding by healthy lifestyle and reverse causation whereby individuals in poor health initiate MV use.
Design, Setting, and Participants
This cohort study used data from 3 prospective cohort studies in the US, each with baseline MV use (assessed from 1993 to 2001), and follow-up MV use (assessed from 1998 to 2004), extended duration of follow-up up to 27 years, and extensive characterisation of potential confounders. Participants were adults, without a history of cancer or other chronic diseases, who participated in National Institutes of Health–AARP Diet and Health Study (327 732 participants); Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (42 732 participants); or Agricultural Health Study (19 660 participants). Data were analyded from June 2022 to April 2024.
Exposure
Self-reported MV use.
Main Outcomes and Measures
The main outcome was mortality. Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% CIs.
Results
Among 390 124 participants (median [IQR] age, 61.5 [56.7-66.0] years; 216 202 [55.4%] male), 164 762 deaths occurred during follow-up; 159 692 participants (40.9%) were never smokers, and 157 319 participants (40.3%) were college educated. Among daily MV users, 49.3% and 42.0% were female and college educated, compared with 39.3% and 37.9% among nonusers, respectively. In contrast, 11.0% of daily users, compared with 13.0% of nonusers, were current smokers. MV use was not associated with lower all-cause mortality risk in the first (multivariable-adjusted HR, 1.04; 95% CI, 1.02-1.07) or second (multivariable-adjusted HR, 1.04; 95% CI, 0.99-1.08) halves of follow-up. HRs were similar for major causes of death and time-varying analyses.
Conclusions and Relevance
In this cohort study of US adults, MV use was not associated with a mortality benefit. Still, many US adults report using MV to maintain or improve health.
JAMA Network article – Multivitamin Use and Mortality Risk in 3 Prospective US Cohorts (Open access)
JAMA Network commentary – The Limited Value of Multivitamin Supplements (Open access)
See more from MedicalBrief archives:
Common vitamin and mineral supplements provide no health benefits
Daily multivitamins linked to slower cognitive ageing — COSMOS-Mind study
Big Pharma and naturopathy — ‘unholy allies’ in the supplementation scam
Adverse effects of non-prescribed vitamins and supplements intake
Meta-analysis: No cardiovascular benefits to dietary supplements except vitamin B