Friday, November 16, 2007

A Tale of Two Studies: Vitamin E - Food vs Supplements

Vitamin E: Food vs Supplements Here is an illustration of the apparent contradiction between whether food sources of vitamin E are better to prevent prostate cancer than supplemental vitamin E sources: Two large studies, both published in the same technical journal at the same time, seem to reach contradictory results as to whether supplemental vitamin E is valuable in relation to prostate cancer. But are they both equal and contradictory? Actually, one is far more rigorous, and thus presumably more valid, than the other. In the first one (Serum and Dietary Vitamin E in Relation to Prostate Cancer Risk <1>), definite and large benefits were shown for supplemental alpha-tocopherol vitamin E, but not for food sources (containing mostly gamma-tocopherol). In the second one (Supplemental and Dietary Vitamin E Intakes and Risk of Prostate Cancer in a Large Prospective Study <2>), only food sources containing gamma-tocopherol were effective, but not supplemental vitamin E as alpha-tocopherol. A closer look reveals that the first study responsibly looked at serum levels and food plus supplemental vitamin E intake, then related that data to prostate cancer rates over up to 19 years afterward. This study's conclusion was that, "In summary, higher prediagnostic serum concentrations of alpha-tocopherol, but not dietary vitamin E, was associated with lower risk of developing prostate cancer, particularly advanced prostate cancer." The second study looked only at questionnaires related to subjects' intake of vitamin E from food and supplements at the start of the 5-year study, then compared the number of cancers over a 5-year period to data obtained from that questionnaire. The incubation period for cancers is estimated to be in the decades, rarely a period of 5 years or less. That, along with the lack of any data on serum antioxidant status and the use of a questionably reliable survey to determine intake of vitamin E from food or supplements, makes the second report far less meaningful than the first one. Don’t get me wrong, I am not against food sources of nutrients and routinely recommend vitamin E sources containing gamma-tocopherol, along with the full range of tocopherols and tocotrienols. But when preliminary or sketchy science is all-too-often reported as if it’s definitive when it’s really not, and when it is contradicted by better science, I am compelled to put things into a more realistic perspective. The measurement of serum levels in the body, along with careful reporting of a nutrient’s intake from various sources, is much more compelling than relying on a questionnaire that may be done by memory. It is well-known among nutritionists that daily food diaries are notoriously different than weekly food surveys done by memory recall, which almost always seem to conveniently forget the junk food, snacks and extra calories. A cancer study lasting nearly 4 times as long is also far more compelling than a shorter one because it will be more likely to encompass the cancer’s incubation period and allow for the development of symptoms that will allow detection. As the National Cancer Institute reports: “Prostate cancer often does not cause symptoms for many years.” <3> The use of supplemental alpha-tocopherol is supported by other reputable studies. For example, The Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study demonstrated a 32% reduction in prostate cancer incidence in response to daily alpha-tocopherol supplementation. <4> Levels of Vitamin E above 100 IU daily are associated with decreased risk of coronary heart disease and certain types of cancer, as well as enhancement of immune function. These increased vitamin E intakes (100 I.U. and above) are considerably above levels obtainable from diet alone. <5-7> In the case of supplemental vitamin E, the results for prostate cancer in the more rigorous, better designed and better implemented study shows that it is more beneficial for prostate health than only food sources of vitamin E, which also tend to be much weaker amounts (often far below 100 IU daily, with Americans’ typical intake being only around 9.5 IU (6.4 mg) of alpha-tocopherol, below the RDA of 22.5 IU (15 mg). <8-9> This indicates our general need for supplemental vitamin E, unless by some miracle we all suddenly decide to eat wholesome natural foods containing a lot more vitamin E. But in the meantime, it would be nice if these studies were put into perspective so we could accurately assess their value to our health habits. Unfortunately, media coverage of negative reports, especially regarding vitamins, tends to drown out the positive ones, even when the good news is backed by studies with better design and implementation. In this case, supplemental vitamin E was the clear winner over the abysmal amounts in our diet, which ideally should be increased to healthy levels. REFERENCES: 1. Weinstein, SJ, et al. Serum and Dietary Vitamin E in Relation to Prostate Cancer Risk. Cancer Epidemiol Biomarkers Prev 2007 16: p. 1253-1259 2. Wright, ME, et al. Supplemental and Dietary Vitamin E Intakes and Risk of Prostate Cancer in a Large Prospective Study. Cancer Epidemiol Biomarkers Prev 2007 16: p. 1128-1135 3. National Cancer Institute’s Web site 4. Weinstein SJ, et al. Serum alpha-tocopherol and gamma-tocopherol in relation to prostate cancer risk in a prospective study. J Natl Cancer Inst. 2005 Mar 2;97(5):396-9. PMID: 15741576 5. Bauernfeind, J. Tocopherols in Foods. In: Vitamin E: A Comprehensive Treatise. Marcel Dekker, Inc., New York and Basel, pp. 99-167, 1980 6. Horwitt, M.K. The Promotion of Vitamin E. J. Nutr. 116:1371-1377, 1986 7. Weber, P., Bendich, A. and Machlin, L.J. Vitamin E and Human Health: Rationale for Determining Recommended Intake Levels. Nutrition 13:450-460, 1997 8. Ervin RB, Wright JD, Wang CY, Kennedy-Stephenson J. Dietary intake of selected vitamins for the United States Population: 1999–2000. Advance data from vital and health statistics; no 339. Hyattsville, Maryland: National Center for Health Statistics. 2004 9. Vitamin E, Office of Dietary Supplements • NIH Clinical Center • National Institutes of Health

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