Supplements vs. exercise: Comparing cancer prevention
strategies
The ‘‘vitamins’’ in your
legs
Dietary supplements are wildly popular in America.
According to the third National Health and Nutrition
Examination Survey, 40% of all American adults take
one or more.
It’s easy to see why supplements are so popular.
Because few are regulated by the FDA, manufacturers
and retailers can assert many benefits and advertise
them aggressively. It’s a good strategy, bringing
more than $20 billion a year to the supplement industry.
But is it good for your health? Are there other ways
to gain the benefits claimed for supplements?
Diet is certainly one alternative; it is clear that
a good diet can reduce the risk of many serious diseases.
Most scientists agree that extra vitamins in pills
or powders add little, if anything, to a well-balanced
diet that adheres to current guidelines. Another alternative
is at hand (or, perhaps, at foot). In fact, regular
exercise is a proven way to achieve many of the benefits
claimed for vitamins and other supplements, even for
people who also eat properly.
Here’s how exercise and supplements stack up
with regard to cancer.
Are supplements safe?
Cancer is the second-leading cause of death in the
United States, taking some 560,000 lives in 2007 alone.
It’s no wonder that possible protection against
cancer is one of the leading reasons that people take
supplements in general and antioxidants in particular.
The idea has great appeal. For one thing, many studies
confirm that people who eat lots of vitamin-rich fruits,
vegetables, and whole grains enjoy a lower risk of
cancer than folks who shun these foods. In theory,
antioxidants should help counter the harmful effects
of free radicals, unstable, high-energy, electrically
charged molecules that can damage DNA and cell membranes.
Cell damage of this sort could increase the risk of
cancer and other diseases. Antioxidants such as vitamin
E, vitamin C, and members of the vitamin A–beta
carotene family can neutralize free radicals, at least
in laboratory experiments.
In the 1980s and early ’90s, antioxidants became
the great hope against both cancer and heart disease.
Sadly, they have been a flop against both (see table
below). Two major randomized clinical trials found
that beta carotene actually increases the
risk of lung cancer in smokers, just the people who
need protection most. A third study reported that vitamin
E increases the risk of second cancers in survivors
of head and neck cancer. And a 2007 meta-analysis of
68 randomized clinical trials involving 232,606 subjects
concluded that beta carotene, vitamin A, and vitamin
E, singly or in combination, may actually increase
the overall death rate in adults.
Clinical trials
of antioxidants |
Trial |
Subjects* |
Vitamin |
Results |
HOPE-TOO |
7,000 patients with
cardiovascular disease or diabetes |
Vitamin E |
No cancer protection |
Vitamins and Lifestyle
(VITAL) Study |
77,000 men and women |
Vitamin E |
Increased risk of
lung cancer, particularly in smokers |
Alpha-Tocopherol,
Beta Carotene Cancer Prevention Study (ATBC) |
29,000
male smokers |
Beta carotene |
Increased risk of
lung cancer in smokers |
Vitamin E |
Decreased risk of
prostate cancer in smokers |
Beta Carotene and
Retinol Efficacy Trial (CARET) |
18,000 smokers and
former smokers |
Beta carotene |
Increased risk of
lung cancer in smokers |
*Round numbers |
The role of supplements in prostate cancer is still
being studied. Beta carotene may offer some protection
against prostate cancer, but only in nonsmoking
men who have very low blood levels due to dietary deficiencies.
According to the ATBC Trial (see table), vitamin E
may reduce the risk of prostate cancer in smokers,
but other randomized clinical trials in nonsmokers
found no benefit. Selenium, a mineral with antioxidant
properties, may reduce a man’s risk of prostate
cancer; the results of individual trials are mixed,
but a Canadian meta-analysis reported a 26% overall
reduction in risk. More study is needed, and the 32,400-person
SELECT Trial of selenium and vitamin E should help
answer these questions. And although many men take
supplements of soy or lycopene to reduce their risk
of prostate cancer, there is no good evidence that
they work. Another ingredient of many popular “prostate
supplements” is zinc, which may actually do more
harm than good. Very large doses of multivitamins or
folic acid may also backfire.
Folic acid, a B vitamin, may help reduce the risk
of colon cancer, at least in women. Harvard’s Nurses’ Health Study linked the prolonged use of
multivitamins containing folic acid with a 75% lower risk of colon cancer. More
research is needed to confirm the findings, but it may be a moot point, since
folic acid added to cereals and other grains has made it easier than ever to
get enough of it from diet, even in people who don’t always get their daily
veggies. And a 2007 study found that very high doses of folic acid — 1,000
micrograms a day, which is two-and-a-half times the Recommended Dietary Allowance — increases
the risk of colon polyps in people with previous polyps;
men may also face an increased risk of prostate cancer.
The authoritative U.S. Preventive Services Task Force
has concluded that vitamin supplements do not reduce
the risk of cancer. Low-dose aspirin may help, but
although you can buy it everywhere without a prescription,
it’s a medication,
not a supplement, and more research is needed to learn if it really helps.
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Evaluating exercise
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