A new study has found that supplements of vitamin C can largely stop the serious depletion of vitamin E that occurs in smokers, demonstrating for the first time in humans a remarkable interaction between these two antioxidants as they work together.
The research also suggests a possible mechanism by which smoking can cause cancer.
The findings are published in Free Radical Biology and Medicine, a professional journal, by scientists from the Linus Pauling Institute at Oregon State University.
The results of the research were based on a placebo-controlled, double-blind clinical study with smokers and non-smokers, and showed that supplements of 1000 milligrams of vitamin C per day could reduce by up to 45 percent the rate of disappearance of one form of vitamin E in smokers. In general, vitamin C supplements helped protect the function and plasma levels of vitamin E, so that smokers who took supplements had about the same level of antioxidant protection as non-smokers.
"A lot of nutrition research in the past has been done by studying one nutrient or another in isolation, sometimes with conflicting results," said Maret Traber, a professor of nutrition at OSU and lead researcher in the Linus Pauling Institute. "What this and other studies like it are showing is that the protection we get from proper diet or supplements often comes from combinations of nutrients working together. This has implications not only for smokers but also for many other people."
Vitamin E is one of the first lines of defense in human lung tissue against the ravages of cigarette smoke, Traber said, which creates destructive free radicals. If the body has adequate levels of vitamin E, this protective antioxidant can interact with the peroxyl radicals created by cigarette smoke and prevent the destruction of lung membranes.
In this process, however, vitamin E can itself be made into a destructive radical. If adequate levels of vitamin C are present, it can help the vitamin E return to non-radical form and continue its protective role. But in the absence of adequate vitamin C, this process breaks down. The new study is one of the first to ever demonstrate this phenomenon in humans.
This and other studies at the Linus Pauling Institute have also shown that in smokers, vitamin E is being depleted from tissue concentrations in order to keep up its levels in the blood.
"We've known for some time that smokers are under oxidative stress, because the smoke itself is an oxidant that creates free radicals and cell mutations," Traber said. "The immune response of the body also tends to cause inflammation, and this inflammation is one reason that smoking relates not only to lung cancer but other serious health problems such as diabetes, hypertension and heart disease."
By having a more rapid loss of protective antioxidants, Traber said, smokers face special challenges.
"Think of a bucket that's filled with water but has holes in it," she said. "If you want to keep the water level, you have to keep adding water. But with smokers, the holes in the bucket are bigger and the water level goes down faster. In the case of nutrition, you have to add more and more nutrients to stay even."