As with many things relating to dietary supplements, the answer is, "that depends." The latest study supports earlier findings on antioxidant supplements and colon cancer. And the results of this antioxidant research may surprise you.
Food vs. Supplements
Decades ago health experts noted that people who eat a lot of antioxidant-rich foods tend to have lower risk of many chronic diseases, including colon cancer. This led to the thinking that antioxidant supplements might also reduce risk of colon and other cancers. But when researchers tested this theory in large groups of people, they were in for a big surprise.
Results Not As Expected
In the 1990s, two randomized controlled trials that included nearly 50,000 participants between them came to the same conclusion. Antioxidant supplements (beta-carotene and vitamin E) do not decrease cancer risk. And in some cases, they markedly increased risk! Back to the drawing board.
It's important to note that antioxidant-rich foods have never been shown to increase cancer risk and consistently appear to decrease it.
After more studies and some hard thinking about why antioxidant supplements increase cancer risk in some people, researchers concluded that certain factors can cause large doses of antioxidants to act like pro-oxidants in the body. In other words, instead of preventing damage due to oxidation, these substances can sometimes promote this damage.
Smoking and Antioxidant Supplements a No Go
The particular cancer type that was studied in the 1990 antioxidant supplement clinical trails was lung cancer. So the studies focused on people at highest risk for this disease, which would be long-time smokers. It turns out that when people who smoke take large doses of antioxidants, particularly beta-carotene and vitamin E, these nutrients can cause more harm than good.
Smoking + Beta Carotene Supplements = More Colon Cancer Risk
There is something about smoking that changes the way the body responds to antioxidant supplements. And it turns out the damage from antioxidants in smokers isn't confined just to the lungs. A 2003 research paper detailed how beta-carotene supplements and smoking can work together to increase colon cancer risk. This research found some interesting things:
- In people who did not smoke cigarettes and who did not drink alcohol, taking a 25 mg beta-carotene supplement REDUCED the risk of getting a colorectal adenoma by 44%. Lower risk of adenomas is linked with lower risk of colon cancer.
- In people who smoked and drank regularly, taking a 25 mg beta-carotene supplement made them twice as likely to have another adenoma. The supplement increased colon cancer risk in this group, by increasing development of growths that can lead to colon cancer.
- For people who either smoked cigarettes or drank alcohol, taking a beta-carotene supplement appeared to slightly increase the risk of getting an adenoma. These results were not significant, according to statistics. This suggests that among people who smoke cigarettes or drink alcohol, taking a beta-carotene supplement likely will not provide health benefits by reducing risk of colorectal adenomas.
New Study: Antioxidants Fan the Flames of Inflammation
The latest study on this topic confirms the potential problems of supplementing with antioxidants. This research focused on people with a history of colorectal adenomas. This group is at increased risk of developing colon cancer because adenomas are growths that can develop into full blown cancer over time.
In this study, 47 people were randomized (selected) to take either a placebo (no supplements) or an antioxidant supplement containing vitamins C and E, beta carotene, riboflavin and niacin (B vitamins), zinc, and manganese. Researchers looked at markers of inflammation in the body throughout the study.
In this study, the people who were smokers and who got the antioxidant supplement had significantly higher levels of inflammation in the body compare with those who got the placebo (both smokers and non-smokers). Given that inflammation can lead to cell damage, and possibly increase cancer risk, this suggests that antioxidant supplements cause more harm than good, especially in smokers.
Bottom Line
With the addition of this latest research, we have yet more proof that for people who smoke, and possibly for people who drink alcohol, taking antioxidant supplements is not the answer to cancer risk reduction.
