Feb 11 2009
Perhaps one of the most common questions I receive from those who wish to utilize science-based medicine for their own health is what I think about vitamins. Even among hard-nosed skeptics, this question is often perplexing. On the one hand, vitamins themselves were discovered by medical and biological science, they play a vital role (by definition) in the healthy functioning of our bodies, and deficiencies of vitamins can cause disease. So they seem perfectly legitimate. On the other hand the market is full of exaggerated and even magical claims about the cure-all power of vitamins.
It’s difficult for people to come to a bottom-line conclusion – should they take vitamin supplements or not. Is it woo or not woo?
Well – it’s complicated. But there is large body of research to help inform our decisions about vitamins. Now, the largest study to date has been published (Multivitamin Use and Risk of Cancer and Cardiovascular Disease in the Women’s Health Initiative Cohorts) looking at 161,808 post-menopausal women over 8 years and finding no benefit for heart disease, cancer risk, or overall survival. This study comes on the heels of other recent studies showing no benefit from routine supplementation.
The recent study
There were two components of this new study. The first pooled data from several trials where multivitamin use was tracked, and also randomized patients to dietary modification, hormonal therapy, and calcium and vitamin D supplementation. The second component of the study was an observational study – which means that multivitamin use was tracked but subjects were not randomized. The study found:
After a median follow-up of 8.0 and 7.9 years in the clinical trial and observational study cohorts, respectively, the Women’s Health Initiative study provided convincing evidence that multivitamin use has little or no influence on the risk of common cancers, CVD, or total mortality in postmenopausal women.
The strengths of this study are its size and duration. Essentially the study had enough power to detect even a modest effect if present. The weaknesses are that the observational part of the study was not controlled. This opens the door to multiple factors that could influence the results.
Some have also charged that 8 years is no sufficient, as benefit from supplementation may manifest only over decades. This is true, but is a generic criticism that can be leveled against any negative study. It doesn’t change the fact that there is still a lack of evidence for routine supplementation. Also, I think that 8 years is a substantial follow up, so if there were a measurable benefit from vitamins this study was probably powerful enough to see it.
On another point, the study’s lead author, Marian Neuhouser, is quoted as saying:
“Get nutrients from food. Whole foods are better than dietary supplements.”
This may be true, but this is not something that can be concluded from this study. Advocates for the preventive benefits of nutrition often make this claim – that nutrition from food is better than nutrition from vitamins. This is partly based on other observational studies that link a diet rich in fruits and vegetables with lower risk of heart disease and certain cancers. However, another way to interpret this discrepancy is not that vitamins from food are better than vitamins from pills but rather that vitamins are not what is healthy about such diets. For example, a diet rich in fruits and vegetables may be healthy because it is not full of animal fat. Or, people who take care to eat such diets may also generally take better care of themselves.
The weakness of observational studies cuts both ways.
To back up a bit – let me say that I am a strong believer in good nutrition. From a basic science point of view, it just makes sense. We need specific nutrients for various biochemical reactions in our bodies. Deficiencies are clearly related to specific diseases. Further, in areas where nutrition is poor overall development is also poor. The connection is clear.
The question of routine supplementation, however, goes further. It asks whether or not taking vitamin supplements are necessary or helpful for someone who has a reasonable diet and does not have any specific disease or condition that would impact their demand for specific vitamins – i.e. routine. In most wealthy industrialized nations lack of quality food is not a problem for most people. Also, modern methods of growing, preserving, and shipping food means that more people have access to a wider variety of foods all year round.
Supplement sellers have tried to perpetuate a myth that foods grown today lack key nutrients. There is just no evidence for this, however. The foods we have access to today have, if anything, superior nutrition to those of the past. Further, botique organically grown crops have only a minor advantage in nutritional content that is not likely to be meaningful.
In short, lack of nutrition does not appear to be a problem for the industrialized west. The modern nutritional scourge is, rather, too much of the wrong kinds of food. This gets back to the point about diets rich in fruits and vegetables – their benefits may be more in what they do not contain than what they do.
Right now the evidence supports the conclusion that for most people who have a reasonable diet there is no benefit from routine supplementation. Of course, what’s a “reasonable” diet? This opens the door for those who wish to take a multivitamin as “insurance” because they feel their diet is not very good. The evidence suggests that they would be better off having a healthy diet rather than living on steak and vitamin pills.
While lacking evidence, the “insurance” argument is not entirely unreasonable. The advice I give my own patients who ask my opinion is this. If you feel you need a supplement because your diet is lacking than go ahead. But – do not take megadoses of vitamins, do not go broke on fancy expensive supplements, and do not use vitamins as an excuse to otherwise have an unhealthy lifestyle. And, in the end your are probably better off working on having a better diet.
None of what I said above has anything to do with targeted supplementation. I prescribe vitamins almost every day – for those with conditions known to be improved or prevented by specific vitamins or co-factors, and for those with a documented deficiency. For example, many patients with certain neurological diseases have low folate or vitamin B12 levels. So I check these frequently and supplement them if the levels are low.
There is evidence that vitamin B2 may improve migraines in some patients – so that is an option I offer migraine patients. B6 may improve recovery from nerve damage (but only at proper doses, megadoses actually causes nerve damage). And folate has been shown to reduce the risk of spinal cord defects, and so should be taken by any woman who might become pregnant (once you find out you are pregnant it’s too late).
Also, there has been much evidence recently about the value of vitamin D in preventing certain cancers and neurological disorders. It may be that the recommended daily allowances of vitamin D were too low, and they are being increased as new evidence comes in.
Targeted supplementation is evidence-based and specific.
There is a clear trend in the evidence we have to date. The benefits of routine supplementation are unproven. High doses of vitamins probably cause more harm than good. If you are concerned about your nutrition then improve your diet.
Further, as with good science-based medicine in general, questions must be specific. We should not ask – do vitamins work. Rather we need to consider specific supplementation in specific situations and conditions.
What may surprise members of the public who have been exposed for years to the propaganda of a supplement industry eager to take their money, or CAM proponents eager to appear legitimate – is that vitamins have always been part of mainstream science-based medicine. There is a tremendous amount of quality research to inform our conclusions about vitamins, and they are part of everyday practice.
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