Do Multivitamins Work?
Do multivitamins work? By now you probably have seen articles like this one published in US News and World Report that taking multivitamins is a waste of time and money. These media reports are based on the results of two studies recently published in the Annals of Internal Medicine.
Both studies have flaws, however. These flaws in these studies include the use of multivitamins that contained inadequate amounts of nutrients, poor adherence rates/high drop-out rates, and unusually high pre-study definition of efficacy.
Adequate nutrient concentration
One common error of any study looking at nutritional supplements is using a supplement that contains inadequate amounts of some key nutrients. In addition, all participants are given the same dose of a supplement in these studies. Are the nutritional needs of 200 pound male the same as 120 pound female?
For example, though a normal blood level of vitamin D is considered 30 ng/ml, levels above 50 and even 60 are associated with more health benefit. Many individuals need to take at least 2,000 IUs of vitamin D in supplement form to achieve blood levels above 50. In the study looking at cardiovascular events after heart attack participants were given a multivitamin that contained a mere 100 IUs of vitamin D. Not enough to make a difference.
The study looking at cognitive benefits use a multivitamin that contained 60 mg of vitamin C, 25 mcg of vitamin B12, and 20 mcg of selenium. These are rather small amounts of these nutrients.
So one of the first questions that should be asked about studies on nutritional supplement is, was the nutritional content a supplement formula used that would be expected to provide health benefits?
Poor Adherence and High Drop-Out Rates
In the cognitive study participants were considered to have been compliant taking their supplement if they took it just two-thirds of the time. In other they were compliant if they did not take the supplement 120 days out of the year. Plus, they were only asked once a year on their adherence to the supplement program.
In the cardiovascular study 46% of the participants discontinued the multivitamin during the study.
Contrary to the many media reports on the results of these Annals of Internal Medicine studies, the cardiovascular study did show some benefit from taking a multivitamin just not enough to meet pre-study efficacy definition. There was an 11% reduction in time to death from any cause, recurrent heart attack, stroke, coronary revascularization, or hospitalization for angina in those taking the multivitamin. There was and 18% reduction in time to cardiovascular death, heart attack, or stroke. The study was designed, however, to detect a 25% reduction in cardiovascular events.
Another complicating factor in the cardiovascular study was the multivitamin group contained a higher rate of diabetics than those who received the placebo. Diabetics are more prone to cardiovascular disease.
The studies published in the Annals of Internal Medicine highlight some of the challenges of designing studies assessing the health benefits of nutritional supplements so that they truly answer what they claim to answer.