Study: Selenium does not protect against lung cancer

reference

Karp DD, Lee SJ, Shaw Wright GL, et al. A phase III, randomized, double-blind, between-group chemoprevention trial of selenium (Se) supplementation in resected stage I non-small cell lung cancer (NSCLC).J Clin Oncol. 2010;28:18s.

design

A double-blind, placebo-controlled study. Participants were randomized 2:1 to receive selenium yeast (200 mcg daily) or placebo for 4 years.

Participant

1,522 patients with stage IA and IB non-small cell lung cancer (NSCLC). Participants had undergone surgical resection of their primary tumor, were cancer-free for at least six months after surgery, were not taking excessive vitamin supplements, and had normal liver function and chest X-rays.

Study medications and dosage

Patients took 200 mcg of selenium yeast daily for 4 years.

Primary outcome measures

Occurrence of a second primary tumor

Key findings

The study was stopped after the 4-year median because participants who received selenium had shorter progression-free survival (PFS) than participants who took the placebo. Variable recurrence rates occurred in less than 2.5 years. After 5 years, 28% of those taking selenium had experienced a recurrence of their cancer, while only 22% of those taking placebo had experienced a recurrence of their cancer (P=0.15).

When the study was stopped, 4.1% of people taking selenium had developed a second primary tumor, while only 3.7% of people in the placebo group had. Overall survival was 5% lower in the selenium group.

Effects on practice

About 80% of the study participants were smokers, and just like the 1996 beta-carotene study, predicted protection against lung cancer failed.¹

As beneficial as antioxidants seem to be in general, selenium can have a paradoxical effect and be dangerous for smokers.

As beneficial as antioxidants seem to be in general, selenium can have a paradoxical effect and be dangerous for smokers.

Preventative medicine researchers have been big fans of selenium for years and often cite Clark et al. from 1996 Nutritional Prevention of Cancer (NPC) as the reason for their use of selenium in cancer prevention. The NPC study examined 1,312 patients who had basal cell or squamous cell carcinoma of the skin. They were randomized to receive either 200 mcg of selenium yeast or placebo and were followed from 1983 to 1991. Although no difference in skin cancer recurrence was found, the study was stopped and the code was broken early; Participants who took selenium had a lower risk of cancer overall (RR: 0.63; 95% CI: 0.47-0.85).²

Stranges et al. reported a double-blind study in 2007 that examined whether 200 μg of selenium per day would prevent type 2 diabetes. No benefit was seen. Rather, participants who achieved the highest serum selenium levels were more likely to develop diabetes.³

In 2008, Reid et al. about a small (N=425) study that took place in Georgia in which participants took 400 mcg of selenium per day. They saw no change in cancer rates.⁴

The effect of selenium on cancer is not as simple as we once thought. This recent study by Karp et al. suggests that selenium does not protect against a second lung cancer; it may actually increase risk, at least in a population of current and former smokers.

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