Vitamin E is best in diet and not supplements
DOES IT WORK?:Some studies have indicated that high doses of vitamin E can be harmful, writes DÓNAL O'MATHÚNA.
VITAMIN E is a mixture of eight different, but very similar, compounds called “tocopherols”.
The fat-soluble vitamin is found in vegetable oils, nuts, whole grains and greens. Vitamin E is an antioxidant, meaning it prevents certain oxidation reactions in the body.
Oxidation of lipids, DNA and other cell components plays a role in the development of heart disease, some cancers and other chronic diseases.
Large observational studies have shown that people’s risk of these diseases is higher when their diet is low in antioxidants, including vitamin E.
The amount of vitamin E naturally present in foods is relatively small, so there has been much interest in (and massive promotion of) vitamin E supplements.
The daily recommended intake of vitamin E for adults is 22 IU (which stands for international units).
A healthy, balanced diet should provide about 20-30 IU of mixed tocopherols. Higher doses (100s or 1000s of IU per day) have been recommended by some to prevent heart disease and other causes of death.
A 2005 systematic review raised concerns that high-dose vitamin E supplementation increased the overall risk of death. Conflicting reports have emerged since then as to whether vitamin E supplements increase or decrease the risk of death. Finding direction through the confusing reports requires understanding important differences between types of research studies.
Evidence from observational studies
The early enthusiasm for vitamin E arose from several observational studies. In this type of study, researchers gather all sorts of information in large questionnaires. People are asked about their diets and other lifestyle factors and information related to their health is collected.
Statistical methods are used to make connections between differences observed. For example, data on people who developed heart disease would be compared to those who didn’t and other differences identified.
A connection between vitamin E intake and heart disease was found this way. However, a crucial guideline with these studies is that correlation does not show causation.
Two factors may change at the same time without one causing the other. A classic example is that skirt hemlines have been correlated with stock market prices; statistically they can be shown to go up and down at the same time, but that doesn’t mean one causes the other.
Evidence from intervention studies
To show causation, an intervention study is needed. In a randomised controlled trial, people are randomly assigned to a group, and each group receives a different intervention (a general term for treatments or therapies).
All other factors are kept the same so that any differences in the results arise from the interventions (ideally, anyway). Observational trials are very important in suggesting what interventions might help. They showed that vitamin E might reduce the risk of heart disease and death.
However, intervention trials are necessary to show if vitamin E supplements actually cause any changes. Until these are conducted, caution and patience are needed.
Intervention studies published in the early 2000s did not show clear benefits from vitamin E supplementation. In fact, some studies found that those taking high doses (over 150 and especially above 400 IU per day) had a slightly higher risk of death (2-4 per cent higher). Last year, a huge international trial (with 35,000 participants) of vitamin E and selenium supplementation was halted early because of a lack of benefits and potential safety concerns with vitamin E.
A Cochrane Collaboration systematic review found that antioxidant supplementation does not prevent chronic diseases and confirmed that vitamin E supplementation leads to a small increase in the risk of death.
Although dozens of trials have been conducted, each is somewhat different. Some have involved people with heart disease; some healthy people; some women only; some men only; and some both; doses have differed and been given for different lengths of time.
All these factors complicate attempts to provide an overall conclusion. Combining the results requires complex statistics, but even the choice of statistical method can influence the overall findings. Such are the challenges of medical research. While we would like clear-cut guidance on what is best for us, sometimes that is not available.
The intervention studies reveal that high-dose vitamin E supplementation does not prevent chronic diseases or reduce the risk of death. Whether it increases the risk of death is less clear-cut. However, even if the risk is very low, given the widespread use of vitamin E supplements, many people could be affected.
Everyone needs some vitamin E, but it is best provided by a balanced diet. As with many areas of life, too much of a good thing can be bad for you.
Dónal OMathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, DCU. He authored Alternative Medicine: The Christian Handbook, Zondervan, 2007