Expensive pee or elixir of life? The two extreme views of multivitamins. I’ve been taking multivitamins for a number of years now. I’ve taken them on faith backed by a little evidence. This week, I think for the first time, a randomised controlled trial has provided high quality evidence that my faith is justified. More on that in a minute.
Most trials of vitamin supplements to date have tested vitamins in isolation. The trials were justified on the observation that people with certain diseases lacked specific vitamins and/or the scientists’ understanding of biochemical pathways that require the vitamin in question to work well. This is well and good. From what I understand most of these trials have failed to show a clinical difference (ie in health outcomes) (see, eg, my report on the Vitamin D trial in Christchurch).
Vitamins (and trace minerals), of course do not exist in us in isolation. They work together with each other and along with all the other chemicals in us with names that only a biochemist could love. The theory, which I’ve accepted largely by faith, is that vitamin supplementation works best when it is multiple vitamins together. Studies of multivitamin supplementation have largely been short term or retrospective observational. That is, scientists have surveyed people on vitamin use and drawn conclusions based on that. One such study, the Iowa women’s study(1), caused me to pause and reassess last year when it seemed to indicate supplementation including copper increased mortality in post-menopausal women. Being neither a woman nor post-menopausal I did not panic.
The prospective randomised controlled trial (RCT) is regarded as a much higher level of evidence than retrospective observational studies. Published this week in the Journal of the American Medical Association (JAMA) is an RCT of multivitamin supplementation in men (2). Briefly, 14641 men aged 50+ were enrolled in a trial in 1997 and followed until 2011. Participants were randomly chosen to receive either a multivitamin or a placebo. Neither the participants nor the people running the study knew which people received placebo and which received multivitamin. This is known as “double-blind.” Only a statistician knew and he or she did not reveal anything until all the data was in. The primary outcome was to compare the rates of cancer and cardiovascular disease in both groups. Secondary outcomes (ie ones that the statistics can not be so precise about because of the numbers) were the rates of some specific cancers (eg prostate cancer). There was amongst the 14641 men a subgroup of about 1300 men with a pre-existing history of cancer.
Men taking multivitamins had a modest reduction in total cancer incidence (HR, 0.92; 95% CI, 0.86- 0.998; P = .04)
My interpretation: Those taking multivitamins were about 8% less likely to get cancer. The statistics show that they are 95% confident that the amongst all men with the same characteristics as the men in their sample the true reduction in probability of getting cancer over the 11 year follow up period is between 0.2 and 14%.
A little frighteningly whilst major cardiovascular events were mentioned as part of the primary outcomes they were not reported on!
The strengths of the study are its size, that it is an RCT and double-blind, that it has good length, that all participants who received the multivitamin received the same one and that the multivitamin manufacturer had no role in designing or running the study, or analysing the data.
The weaknesses are that it is all men, all over the age of 50, and all physicians.
S0, is my faith justified? If by that do you think I mean “proven” then think again. Proof or proven are words that should never be used in the company of good scientists. Rather, I think there is some more good quality evidence to support the taking of multivitamins – so I shall continue to do so. I must, though, remain open to evidence of the opposite variety and be aware that like all studies there is a probability that the conclusions will not be backed up by future studies.
Of course not all multivitamins are created equal (beware of fillers), they have different compositions and some are less likely to be absorbed than others, so do some homework before you rush out an buy some.
(1) Mursu J, Robien K, Harnack LJ, Park K, Jacobs DR. Dietary supplements and mortality rate in older women: the Iowa Women’s Health Study. Arch Intern Med 2011;171(18):1625–33.
(2) Gaziano JM. Multivitamins in the Prevention of Cancer in MenThe Physicians’ Health Study II Randomized Controlled TrialMultivitamins in the Prevention of Cancer in Men. JAMA : the journal of the American Medical Association 2012;:1.
[Conflict of interest: My wife's business includes the selling of multivitamin supplements]