A daily multivitamin does not increase the risk of death, says a new meta-analysis from Australia that supports the safety of the supplements and challenges previous controversial analyses.
Writing in the American Journal of Clinical Nutrition, scientists from Swinburne University of Technology report that multi-vitamin and –mineral supplements did not affect the risk of mortality from cancer or vascular causes.
In addition, a “trend” was observed for a reduced risk of all-cause mortality, but this did not reach statistical significance.
“By performing a meta-analysis of RCTs, the current study provides the highest level of evidence to indicate that multivitamins supplementation has no significant effect on the risk of all-cause mortality, mortality of vascular etiology, or mortality due to cancer,” wrote the authors, led by Helen Macpherson.
Links between supplements and ‘all-cause mortality’ have been controversial, with a 2007 meta-analysis in the Journal of the American Medical Association (Vol. 297, pp. 842-857) reporting that antioxidant supplements are linked to a 16% increase in mortality risk.
The initial JAMA meta-analysis included 66 randomized trials with antioxidant supplements, including vitamins A, C and E, and beta-carotene. Over 400 clinical trials were excluded from the analysis because no deaths were reported.
Following criticism of the initial JAMA article (corrections were published in JAMA, 2008, Vol. 299, pp. 765-766), the authors republished their meta-analysis in the prestigious Cochrane Systematic Review.
A re-analysis of this meta-analysis by a group of well-respected antioxidant experts led by Prof Hans Biesalski from the University of Hohenheim found that 36% of the trials showed a positive outcome or that the antioxidant supplements were beneficial, 60% had a null outcome, while only 4% found negative outcome (Nutrients, 2010, Vol. 2, pp. 929-949).
Regarding multi-vitamins, data from the Iowa Women's Health Study, published in the Archives of Internal Medicine (2011, Vol. 171, pp.1625-1633), found that multivitamins increased the so-called absolute mortality risk by 2.4%.
The Iowa study was an observational study, not the meta-analysis of the randomized clinical trials reported by Macpherson and her co-workers.
The Swinburne researchers analyzed 21 scientific articles, providing data on 91,074 people and 8794 deaths.
Only studies that lasted for at least one year were included and studies with people with terminal illnesses were excluded.
Results showed that the average participant was 62 years old and took multivitamins and minerals for an average of 43 months.
No link between all-cause mortality was observed by the researchers.
The researchers noted that multivitamins are used extensively in developed countries, where consumers are “more likely to meet their daily vitamin requirements from dietary sources.
“This is an important issue because the safety of multivitamins use may be influenced by the level of nutrient intake from dietary sources and concomitant supplement use.
“As most commercially available multivitamins approximate the recommended daily value, excessive nutrient intake may be more likely in those who use multiple dietary supplements than in those who take a daily multivitamins.
“Reducing the likelihood of polysupplementation, most studies we reviewed either excluded participants who were regular vitamin users at the time of enrollment or requested that participants discontinue relevant supplementation for the trial duration.
“Therefore, the safety of multivitamins identified in this review may be less applicable to those who supplement with a multivitamin in addition to individual vitamins.”
The authors note that they have previously received funding from Swisse Vitamins Pty Ltd.
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.112.049304
“Multivitamin-multimineral supplementation and mortality: a meta-analysis of randomized controlled trials”
Authors: H. Macpherson, A. Pipingas, M.P. Pase