Your Cancer Risk - Vitamins Minerals And Your Health: Vitamins And Minerals What You Need To Know

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Your cancer risk

Many health-conscious people believe that specific foods can affect their cancer risk. While there is no doubt that overall diet affects the risk of developing some types of cancer, researchers are divided about whether specific vitamins, minerals, and other nutrients can actually prevent cancer.

It would make sense that certain foods and beverages might prompt cancerous cells to develop, while other foods might confer protection. That is because some foods contain carcinogens that can damage the DNA in cells, leading to the out-of-control cell growth characteristic of cancer. For example, eating too much of pickled or salt-cured foods, which contain carcinogenic nitrosamines, appears to raise the risk of stomach cancer. Other foods act as promoters, fueling the growth of cancer once it's begun. Alcohol falls into this category, which is why heavy alcohol consumption — whether beer, wine, or hard liquor — has been linked to a higher rate of cancers of the mouth, liver, esophagus, and breast. Yet other foods contain antioxidants that prevent such DNA damage or support the body's own repair mechanisms. That is why the experts recommend eating fruits and vegetables, which are loaded with antioxidants.

Multiple observational studies (looking at the incidence of cancer in various populations, for example) and retrospective studies (which ask cancer patients to recall what types of food they've eaten in the past) have supported a strong link between consumption of certain foods and the development of cancer. Yet in the past decade, findings from large epidemiological studies (which track healthy people over time and see what happens) have undermined the earlier conclusions. For example, some of these studies have concluded — contrary to what was believed previously — that consumption of fat, fruits and vegetables, and meat seems to have little impact on the development of breast cancer.

What is going on? It's not clear. Although researchers still believe that dietary factors play a role in cancer development, they think the earlier studies may have been flawed in several ways. First, people diagnosed with cancer, in an effort to determine what went wrong, may overestimate the number of unhealthy foods they ate in the past — a phenomenon known as recall bias. Second, insight into healthy eating habits often comes from studying the eating habits of healthy people — who are also likely to engage in other habits like exercising, maintaining a healthy weight, and not smoking. As a result, the cancer-protective impact of food may be hard to tease out. Finally, it appears that diet early in life may be more important than diet later in life, because cancer takes so long to develop.

To further complicate matters, a 2005 study concluded that high doses of antioxidants might actually reduce the anti-cancer effects of chemotherapy and radiation. If you are undergoing treatment for cancer, it's important to talk with your medical oncologist or radiation oncologist before taking any supplements.

Yet even with all these caveats, the research continues to provide some insight into the way that particular vitamins and supplements may protect against specific cancers. And as further studies are published, it may become clearer how all these puzzle pieces fit together so that researchers can provide more specific advice about diet and cancer.

Folic acid

Insufficient folic acid may damage DNA in ways that lead to cancerous changes. Observational studies suggest that people who consume more folic acid are less likely to develop colon cancer. In the Health Professionals Follow-Up Study, men who took multivitamins containing folic acid for more than 10 years cut their colon cancer risk by 25%. Women enrolled in the Nurses' Health Study who took multivitamins with folic acid for at least 15 years reduced their risk for colorectal cancer by 75%. Another large study — the National Health and Nutrition Examination Survey (NHANES) — found that folic acid supplementation decreased the risk of colon cancer by 60% in men, but the reduction in risk was not significant among women.

Other research suggests that greater consumption of folic acid can lower breast cancer risk, at least among women who drink alcohol and have low folic acid levels. Alcohol consumption is believed to increase the risk of some cancers, including breast and colon cancers. But folic acid seems to counteract, in part, the adverse effects of alcohol.

Vitamin C

There is moderately strong support for the theory that foods rich in vitamin C lower the risk for developing some cancers, including those that attack the mouth, esophagus, stomach, and breast. According to two studies, published in the Lancet and the American Journal of Clinical Nutrition, men (but not women) who didn't get much vitamin C through their diets had higher total cancer death rates. Another analysis, covering data from 26 separate studies, noted a 20% decline in breast cancer risk among women whose diets were high in vitamin C.

Not all studies agree, however. An observational study of Swedish women, published in the International Journal of Cancer in 2001, lent credence to the idea that vitamin C–rich foods might play a role in reducing breast cancer — but only among women who were overweight or who had diets high in linoleic acid (a substance found in safflower oil and some margarines). Another study, which compared baseline vitamin C blood levels from 14,625 American women with later occurrence of breast cancer, found no evidence that vitamin C affected cancer risk.

The research continues, but it appears that the best thing to do is to follow a healthy diet so that you will obtain sufficient quantities of vitamin C from food. And it is not yet clear whether vitamin C in foods is the true hero or if other substances in fruits and vegetables are at work. Meanwhile, no strong studies have found anticancer benefits in vitamin C supplements.

Vitamin D

In test tubes, at least, vitamin D blocks growth and replication of various cancer cells, including those that attack the breast, ovaries, prostate, and colon. Higher blood levels of vitamin D have been linked with reduced risk of colon and colorectal cancers. And two studies published in 2005 in the Journal of the National Cancer Institute support the idea that sunlight exposure, which enables the body to produce vitamin D, may reduce risk of non-Hodgkin's lymphoma and, amazingly, may even increase survival rate for people with skin cancer. Other emerging data indicate that vitamin D levels may lower the risk of developing a number of cancers. For example, some evidence (although not definitive) suggests that one reason African American men have much higher rates of prostate cancer may be that, in general, they don't get enough of this nutrient.

Vitamin E

So far, vitamin E appears to play no strong role in diminishing cancer, except possibly prostate cancer. For example, the Alpha-Tocopherol, Beta Carotene (ATBC) trial, a randomized controlled study reported in the New England Journal of Medicine in 1994, assessed the effects of vitamin E and beta carotene supplements on lung and other cancers in 29,000 male smokers. Four separate groups received daily doses of either 50 mg of vitamin E, 20 mg of beta carotene, both vitamin E and beta carotene, or a placebo. The vitamin E supplements had no effect on the development of lung cancer and a number of other cancers, with one notable exception: The researchers found that fewer cases of prostate cancer occurred among the participants given vitamin E. While not all other studies support this finding, two others have found that vitamin E supplements reduce prostate cancer risk, particularly in smokers.

These studies focused on a form of vitamin E called alpha-tocopherol. Interestingly, a few studies on gamma-tocopherol, another form of vitamin E, have found that it, too, modestly reduces prostate cancer risk. However, other studies found it had no effect. More study is needed before any definitive information will be available.

Meanwhile, research on other types of cancer continues to show that vitamin E is not protective. For example, a 2005 study analyzed the effects of vitamin E supplementation over eight years among 540 people who had previously been treated for head and neck cancers (including cancers involving the lip, mouth, throat, voice box, nose, sinuses, or salivary glands). Taking 400 IU of vitamin E per day did not keep cancer at bay, but instead actually increased recurrence risk.

Carotenoids

Because of beta carotene's antioxidant activity in the body, researchers originally had great expectations for its cancer-battling potential. But these hopes were dashed by a number of disappointing studies. For example, several studies found that beta carotene did not reduce the risk of prostate cancer. Even more worrisome, initial findings of the ATBC trial indicated that beta carotene supplements actually seem to increase the rate of lung cancer in smokers — although much of this increased risk was clustered among those who smoked more than a pack of cigarettes a day and drank regularly. To further muddy the waters, when researchers continued to follow ATBC study participants, they found a significant decrease in lung cancer in the beta carotene group later on, which more than canceled out the earlier increase. Even so, the researchers continued to advise smokers to avoid taking beta carotene supplements.

The evidence is stronger for the protective benefit of two other carotenoids: lycopene, which lends the red tint to tomatoes, and alpha carotene, found in carrots. A report that combined data from more than 122,000 women and men enrolled in the Nurses' Health Study and the Health Professionals Follow-Up Study considered whether the risk for lung cancer was affected by diets rich in several carotenoids: alpha carotene, beta carotene, lycopene, lutein, and beta cryptoxanthin. The results, published in the American Journal of Clinical Nutrition in 2000, indicate that lycopene and alpha carotene lower lung cancer risk. Among people who had never smoked, the risk of lung cancer declined by 63% for those whose diets supplied the most, rather than the least, amount of alpha carotene. And over all, people who ate large amounts of a variety of carotenoids were 32% less likely to die of lung cancer than those who ate the least. Two other observational studies, including one that drew on data from the Nurses' Health Study, also imply that alpha carotene may lower the risk of lung cancer. In that study, eating five or more carrots a week cut risk substantially.

Lycopene was linked to reduced risk of prostate cancer in several studies. One, from the Journal of the National Cancer Institute in 1995, focused on a variety of carotenoids. Only lycopene — primarily from tomatoes and pizza — appeared to reduce risk significantly. According to this study, tomato sauce and juice were also associated with a lower risk of prostate cancer. The few studies that have examined whether blood levels of lycopene affect prostate cancer risk tend to show that men with lower levels have higher rates of prostate cancer.

Selenium

This mineral flexed its muscles nicely in lab studies, where it reduced the risk of some cancers in animals. That made sense biologically, because selenium is a component of a key antioxidant enzyme. It also enhances the action of vitamin E. Where people are concerned, though, its usefulness as a cancer fighter is not quite clear.

Only one randomized controlled trial has looked at this question. A 1996 study in the Journal of the American Medical Association examined whether selenium could help prevent two types of skin cancer in people with a history of one or the other. Some of the 1,300 subjects received 200 mcg of selenium a day (nearly four times the recommended dose) while the rest received a placebo. Selenium didn't affect the rate of new skin cancers, but it did significantly reduce deaths from, and new cases of, all cancers combined. It also lowered the rates of lung, colorectal, and prostate cancers. But the Nurses' Health Study has found that a high intake of selenium failed to reduce rates of any type of cancer — so clearly more research on the issue is needed before physicians will know for sure.

Early indications are that selenium may help protect against one type of malignancy: prostate cancer. In addition to the 1996 study cited above, a 1999 study drawing on data from the Health Professionals Follow-Up Study found that men consuming 200 mcg of selenium a day had one-third the incidence of prostate cancer as men who had less in their diet. The ongoing Selenium and Vitamin E Cancer Prevention Trial (SELECT) of over 35,000 men should shed further light on any prostate cancer link.

Figuring out how much selenium people eat is particularly difficult because the amount of selenium in a given plant food depends on how much selenium was in the soil where the plant was grown. The amount of selenium varies widely from one region to another. Thus, a food grown in one area may have much more selenium than the same kind of food grown in a different area.

Calcium

Currently, the Institute of Medicine recommends 1,000–1,200 mg of calcium a day for adults, depending on age. But some experts believe that less is warranted, based in large part on studies that have linked diets high in calcium to certain cancers. Data from the Health Professionals Follow-Up Study suggest that a diet very rich in calcium might raise the risk for prostate cancer. It found that men who got more than 2,000 mg of calcium a day were almost three times as likely to develop advanced prostate cancer as men who got less than 500 mg a day. The Nurses' Health Study investigators noted that milk, which is a major source of calcium, might contain another substance that raises ovarian cancer risk. The risk, if it is real, is probably not caused by calcium itself — since calcium supplements seem safe for women — but by the high levels of natural hormones found in milk.

These findings are certainly not conclusive, but the research does raise important questions about how much calcium is optimal. In the meantime, if you enjoy dairy products, don't fret over having a glass of milk a day. Men should avoid routinely taking calcium supplements and be wary of overdoing it with dairy products.

Last updated:	January 23, 2007