Long-term and high dose supplementation with vitamin E may result in a "small increased risk" of lung cancer, most notable amongst smokers, says new research.
No benefit or harm was observed for intake of multivitamins, vitamin C, or folate, according to the study of 77,721 men and women aged between 50 and 76 published in the American Journal of Respiratory and Critical Care Medicine.
"Our study of supplemental multivitamins, vitamin C, vitamin E and folate did not show any evidence for a decreased risk of lung cancer," wrote lead author Christopher Slatore from the University of Washington, in Seattle. "Indeed, increasing intake of supplemental vitamin E was associated with a slightly increased risk of lung cancer."
On the surface, the study appears to add to a small quantity of 'bad press' for vitamin E, following earlier, but much criticized, studies linking the vitamin to an increased risk of "all-cause mortality", for example (Annals of Internal Medicine, 2004).
However, according to Pamela Mason, spokesperson for the Health Supplements Information Service (HSIS), the "study results are not all that surprising." The HSIS is an educational programme affiliated with the Proprietary Association of Great Britain, which represents manufacturers of OTC medicines and food supplements in the UK.
"Vitamins are essential nutrients that act to maintain health and prevent vitamin deficiency. They were never intended to be used to prevent chronic disease such as cancer. Indeed, it would be asking a lot of a vitamin pill to expect it to prevent cancer," she said.
"When given as supplements, vitamins help to make up dietary gaps caused by poor diets, which are a problem for significant numbers of people in this country - young and old," added Mason.
It should also be noted that the research challenges the findings of a meta-analysis by researchers from Brigham and Women's Hospital and Harvard Medical School, which pooled eight prospective studies with a total population size of 430,281 participants (International Journal of Cancer, Vol. 118, pp. 970-978).
The meta-analysis found that high intake of vitamins A, C, E and folic acid do not reduce the risk of lung cancer. Moreover, when supplement sources of the four micronutrients was examined, not link was found between lung cancer risk and nutrient intake for the entire sample population, but was linked to a "modest increase in lung cancer risk among women." This was said to be due to chance and did not have biological implications.
Participants in the new study were enrolled in the Washington state VITAL (VITamins And Lifestyle) study, and the rate of developing lung cancer was followed over ten years.
During the course of the study, 521 subjects developed lung cancer, many of which could be linked to smoking history, family history, and age. However, Slatore and co-workers calculated a small but significant association between use of supplemental vitamin E and lung cancer.
Specifically, for every 100 milligram per day increase in dose of vitamin E, the risk of lung cancer among smokers increased by 11 per cent, and by five per cent for the whole study population.
"In contrast to the often assumed benefits or at least lack of harm, supplemental vitamin E was associated with a small increased risk of lung cancer," said Slatore.
On the other hand, no change in the risk of lung cancer, positively or negatively, was observed for supplements of multivitamins, vitamin C, and folate.
Currently, smokers are not recommended to consume beta-carotene supplements following reports that the carotenoid may increase their risk of lung cancer.
Diet versus supplements
The study adds to the debate between dietary and supplemental sources of vitamin E. Slatore said that the findings could have broad public health implications, given the large population of current and former smokers and the widespread use of vitamin supplements.
"Future studies may focus on other components of fruits and vegetables that may explain the decreased risk [of cancer] that has been associated with fruits and vegetables," he wrote.
"Meanwhile, our results should prompt clinicians to counsel patients that these supplements are unlikely to reduce the risk of lung cancer and may be detrimental."
Researchers from Finland reported that a diet rich in vitamin E may protect middle-aged male smokers from dying from diseases such as certain cancers and coronary heart disease.
The 19-year study reported that men with the highest serum alpha-tocopherol levels (more than 13.5 mg/L) had significantly reduced risk of cause-specific mortality than those with the lowest levels (less than 10 mg/L). Indeed, mortality due to lung cancer, prostate cancer, coronary heart disease, stroke, and respiratory diseases were found to be reduced by 21, 32, 16, 36, 42 per cent, respectively, for men with the highest serum levels, compared to men with the lowest levels.
The results contrast with the results of supplementation trials. "Because supplemental vitamin E has not been shown to reduce mortality in randomised trials, efforts to improve vitamin E status through dietary means may be warranted, particularly if future prospective studies show similar serum alpha-tocopherol -mortality associations in diverse populations, including non-smokers," concluded the Finnish researchers.
Source: American Journal of Respiratory and Critical Care Medicine
1st March 2008, Volume 177, Pages 524-530. doi:10.1164/rccm.200709-1398OC
"Long-Term Use of Supplemental Multivitamins, Vitamin C, Vitamin E, and Folate Does Not Reduce the Risk of Lung Cancer"
Authors: C.G. Slatore, A.J. Littman, D.H. Au, J.A. Satia, E. White