Is it all in their heads? Experts criticize assumptions, structure of BMJ paper that blasts multivitamin use
The study, written by a lengthy list of experts from institutions such as Harvard and Yale medical schools and other hospitals and institutes, was published online yesterday in the BMJ Open journal.
The authors used data from the 2012 National Health Interview Survey. They examined records from almost 5,000 self reported vitamin users and more than 16,000 non users. Multivitamin and mineral (MVM) users were found to be older and in higher income brackets, a finding that squares with previous research. They were also found to be in generally better baseline health and were more likely to have health insurance.
Baseline assumption: No correlation between MVM use and better health outcomes
The researchers started their analysis with an assumption of no clinically relevant effects of MVM usage on health outcomes.
“The consumption of non-prescription, over-the-counter MVMs has not produced robust evidence for the wide-ranging health benefits expected by the general adult population. Likewise, large randomised clinical trials that evaluate MVMs at different doses, across both men and women at various ages, have failed to demonstrate benefit in prevention of chronic diseases,” the authors wrote in their introduction.
The authors said MVM usage has not been shown to reduce the incidence of heart disease. The data is inconclusive when it comes to the role of MVM use in supporting cognitive function. Nor have the products been shown to improve the picture in all cause mortality, the authors wrote.
Placebo effect, broadly speaking, accounts for MVM popularity
The researchers found that while 30% of MVM users reported that the products improved their overall health, that is not corroborated by the data on health outcomes. The authors speculated that a variant of the placebo effect is at work to explain why these products are so popular when, in their view, they cannot be shown to ‘work.’
“The results here suggest two potential explanations underlying widespread MVM consumption in the absence of clinically measurable benefits: MVM users believe in the efficacy of MVMs by harboring a positive expectation regarding the health benefits of MVMs; and MVM users intrinsically harbor a more positive outlook on their personal health regardless of MVM usage,” the authors wrote.
“Our study reveals that MVM users self-report better overall health than non-users despite not exhibiting improved health by clinically measurable standards,” the authors concluded.
CRN: Conclusions shouldn’t undermine the legitimate uses of multivitamins
Andrea Wong, PhD, senior vice president of scientific and regulatory affairs for the Council for Responsible Nutrition, said the study has a number of issues with its methodology which call into question the authors’ conclusions.
“The many limitations and shortcomings that hinder this study must be taken into account, only some of which are acknowledged by the study’s own authors. For instance, the results of the study are based on survey data, so rather than being determined by a clinician, all measured outcomes are self-reported and therefore, less reliable. The study also does not capture the composition of the multivitamin or multi mineral products reported by respondents or the duration or frequency of consumption,” Wong said in a statement.
By law a dietary supplement such as multivitamin cannot claim to treat or prevent any disease. Wong noted that primary role of these products has been to fill in well known and officially recognized nutrient gaps in the American diet.
“CRN reminds consumers that the primary role of a multivitamin is to fill nutrient gaps and to ensure the public gets the recommended levels of nutrients essential to everyday life. Government data repeatedly demonstrates that Americans fall short in getting the appropriate amount of essential nutrients they need,” she wrote.
“The conclusions of the study are a disservice to the public and should not influence consumers’ decision to take a multivitamin or other dietary supplement product. As data continues to show that Americans, particularly low-income populations, do not get the essential nutrients needed from diet alone, taking a multivitamin is a convenient and affordable way to ensure consumers get the nutrients they need,” she added.
Blumberg: Structural shortcomings swamp any hope of reasonable conclusions
Prof Jeffrey Blumberg, PhD, research professor at the Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy at Tufts University, said the cross sectional nature of the study, consisting of a snapshot in time in 2012, would prevent making a correlation between MVM use and health outcomes in any case, even if the authors had not gone into the exercise with their ‘no benefit’ assumption.
“It’s a cross-sectional study. There is no before and after. The only way to demonstrate outcomes like that would be to follow subjects through a longitudinal study. In that respect this is a fundamentally flawed approach to address the question they’re asking. I note that 50% of the discussion in this study was on the limitations of the study, but that didn’t seem to impair them from drawing some pretty strong conclusions,” Blumberg said.
In addition, Blumberg noted that there was no information on the kind of products being consumed. ‘MVM’ as a designation casts a very wide net.
“This covers all kinds of products and we don’t know anything about them. There is no information about the actual formulations and then they want to draw conclusions about outcomes,” he said.
Nor, Blumberg said, is there any data on how the products were being used.
“It’s like saying blood pressure pills don’t work in this cohort without asking whether they took pills or how often they took the pills. There is no dose response or dose duration information here,” he added.
Source: BMJ Open
Volume 10, Issue 11
Self-reported health without clinically measurable benefits among adult users of multivitamin and multimineral supplements: a cross-sectional study
Authors: Paranjpe MD, et al.
