Vitamin E Supplements, Lung Cancer Risk Needs Further Review - ATBC Study

Further review of the effects of vitamin E supplementation on lung cancer risk among male smokers is recommended by Alpha-Tocopherol, Beta Carotene Cancer Prevention (ATBC) Study researchers in a report published in the Oct. 20 issue of the Journal of the National Cancer Institute.

"While it is tempting, based on the present data, to speculate that the administration of greater quantities of [alpha]-tocopherol (i.e., >50 mg daily) might have produced a substantial reduction in lung cancer incidence in the ATBC study, only future studies, and controlled trials in particular, can shed light on this question," Karen Woodson, PhD, National Cancer Institute, et al. conclude.

The authors also suggest additional studies in women and nonsmokers, as well as those bridging a wider range of ages and length of time smoking.

"Additional prospective studies of vitamin E status and lung cancer that include women and nonsmokers and that assess the association across a spectrum of lung cancer risk (e.g., especially age and smoking exposures) will be particularly informative," Woodson et al. state.

Results from the ATBC trial indicate an inverse association between serum alpha-tocopherol, dietary alpha-tocopherol and dietary vitamin E in all forms, and incidence of lung cancer. However, only dietary alpha-tocopherol and dietary vitamin E reached statistical significance in a comparison of the top quintile versus the lowest quintile of intake. Serum alpha-tocopherol levels in the highest quintile demonstrated a trend toward significance.

The researchers observed an estimated reduced lung cancer risk of 19%, 20% and 23% for serum alpha-tocopherol, dietary alpha-tocopherol and dietary vitamin E, respectively. A similar association was observed between serum alpha-tocopherol and lung cancer mortality.

The ATBC trial, conducted in Finland, examined the relationship between alpha-tocopherol and beta carotene intake and the incidence of primary cancer of the lung or bronchus in 29,102 male smokers between the ages of 50 and 69. The men were randomized to receive 50 mg/day alpha-tocopherol, 20 mg/day beta carotene, neither or both.

Participants were recruited between 1985 and 1988 and were followed until death or Dec. 31, 1994, for an average follow-up period of 7.7 years.

At baseline, general medical history, diet, smoking history and other background information was collected, along with a fasting blood sample. The blood sample was analyzed within two years in order to minimize the risk of alpha-tocopherol degradation. Incident cases of lung cancer were diagnosed in 1,144 men during up to 10 years of follow-up.

"This controlled trial did not provide evidence of lung cancer prevention from [alpha]-tocopherol supplementation overall," the authors state.

However, when the researchers examined the effect of dietary supplementation on subgroups of the study cohort, a significant effect was seen in participants under 60 and those who had smoked less than 40 years.

"Higher [alpha]-tocopherol status might be protective only in such a lower risk setting," the authors conclude. "It is also possible that high [alpha]-tocopherol levels slowed the progression or growth of subclinical tumors among these subgroups, such that their clinical manifestation and diagnosis were delayed beyond the period of observation."

The beneficial relationship for higher pretrial alpha-tocopherol status was observed primarily among subjects given supplements, which "suggests synergism between usual intake and the controlled intervention," the researchers say. "The...findings reinforce the importance of adequate vitamin E status to lung cancer risk, particularly among smokers."

Previous findings from the ATBC study indicated a 16% increased risk of lung cancer in smokers who received 20 mg/day beta carotene. A secondary analysis showed the effect was more pronounced in participants with high intakes of alcohol and those who smoked more than 20 cigarettes per day.

Study data also have demonstrated a link between long-term vitamin E supplementation and a lowering of prostate cancer incidence and death among male smokers (¹ (Also see "Smokers "should avoid high-dose beta carotene supplementation" -- new ATBC analysis." - Pink Sheet, 11 Nov, 1996.)). Among other findings, alpha-tocopherol has been shown to help prevent pre-eclampsia and non-fatal myocardial infarction, and to assist in cognitive functioning.