Men and women from a cancer-plagued region of China who took selenium, vitamin E and beta-carotene have a reduced risk of dying that persists for up to a decade after they stopped taking the supplements, a new study out in the Journal of the National Cancer Institute shows.
Given that people in the study were "nutritionally deprived," Dr. Philip R. Taylor of the National Cancer Institute in Bethesda, Maryland, and his colleagues say, the findings may not be relevant to better-nourished populations.
But Taylor and his team did find that while the nutrient combo cut the risk of esophageal cancer in people younger than 55, it actually upped risk in older people. And this, Taylor told Reuters Health, may indeed have larger implications.
In the rural village of Linxian, rates of esophageal cancer and stomach cancer are among the world's highest, and nutrition is poor. Taylor and a group of Chinese and US colleagues conducted a large trial to determine if giving them one or more of four different combinations of vitamins and minerals might reduce villagers' cancer risk. The study included 29,584 people 40 to 69 years old who took the supplements for five years and were then followed for another 10 years.
One combination, "Factor D," consisting of 50 micrograms of selenium, 30 milligrams of vitamin E, and 15 milligrams of beta-carotene, reduced overall mortality, cancer mortality, and the risk of developing stomach cancer among people who took it for five years. The three other nutrient combinations had no effect on mortality.
Ten years later, the researchers found, people who had taken Factor D were still 5% less likely to die from any cause than people who didn't take the supplement, and were 11% less likely to die from stomach cancer. Nearly all of the effect was seen among people 55 and younger. While Factor D cut esophageal cancer risk in people younger than 55, it actually increased risk in older people.
A raft of clinical trials of micronutrients for cancer prevention were launched following the publication of the Linxian study's initial results. But the results have been disappointing so far; in fact, some studies suggest that certain nutrients actually boost cancer risk.
What's important about this follow-up report, Taylor said, is that it provides "proof of principle" that giving people supplements to correct nutritional deficiencies can indeed prevent cancer. But megadoses in Western populations are a different story, he said.
The fact that benefits in the current study were limited to younger people, he added, suggests "we need to attack the problem earlier in the process to be effective, rather than later." And because cancer is characterized by out-of-control growth, Taylor pointed out, by giving micronutrients too late "we might in fact at that point be feeding the cancer."
Based on the findings, Taylor said, it looks like the most important thing may be to have adequate amounts of nutrients early-on, and that taking high doses of certain vitamins later in life won't help and may in fact be harmful. "At this moment, it just doesn't look like it's the thing to do," Taylor said. "It's back to Ben Franklin and everything in moderation."