Vitamin supplements and cancer risk
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| Vitamin supplements and cancer risk |
Dietary supplements such as vitamin and mineral tablets have
become widely available in Australia and may be taken for a variety of reasons.
Some people are advised by their doctor or dietitian to take dietary
supplements if they have certain medical conditions, are pregnant, or have a
restricted dietary intake. However, the majority of people do not need dietary
supplements if they eat a wide variety of nutritious foods.
Cancer Council recommends people eat a variety of nutritious food especially
Supplements versus whole foods
Getting nutrients from tablets is not as good as getting them
naturally from food. Foods like fruit and vegetables contain lots of vitamins,
but also many other beneficial substances such as fiber, minerals, and
antioxidants. Dietary fiber can help to ensure a healthier digestive system and
reduce the risk of bowel cancer, while antioxidants help protect against the
damaging effects of free radicals in the body. Therefore eating whole foods is
best to obtain maximum benefits.
In addition, research has shown that some vitamins that are
taken as supplements may not have the same effect as when they’re consumed in
food. This is because the effect of the vitamin may be due to interactions between different food compounds that don’t
occur when vitamins are isolated in a supplement.
Cancer Council recommends
people obtain their nutritional requirements from whole foods, rather than
individual nutrients in a supplement form.
Eating nutritious foods like fruit and vegetables can also help you to maintain
Supplements and cancer risk
Studies suggest that people who eat a diet high in plant foods
such as fruit, vegetables, and wholegrain cereals have a lower risk for some
types of cancer.
However, in most cases, it is not known which compounds (or
combination of compounds) are best when it comes to lowering the risk of cancer.
There are likely to be important, but as yet unidentified, components of whole
food that are not included in supplements.
Currently, there is no evidence to suggest that supplements (e.g.
tablets, capsules) can reduce cancer risk. The few clinical trials testing
whether supplements can reduce cancer risk in humans have had disappointing
results. Any link between diet and cancer is far more complex than simply
adding vitamin supplements to your existing diet.
Beta-carotene
Some studies suggest that certain antioxidant supplements such
as beta-carotene is not protective, and may in fact increase overall
mortality.
Beta-carotene is the orange color pigment found in vegetables
and fruit and is converted into vitamin A in the body. Normal levels of
beta-carotene from foods such as dark-green leafy vegetables, carrots, sweet
potato, mango, and dried apricots may help protect against cancer.
However, studies have shown that there is a convincing link
between beta-carotene supplements and the risk of lung cancer in people who
smoke cigarettes.
Therefore it is possible that the protective effect of
beta-carotene at dietary intake amounts is lost or reversed with dietary
supplementation and the higher levels that this can supply.
Cancer Council recommends people avoid taking high doses (>18 mg) of beta-carotene supplements, especially if they smoke.
Vitamin A (retinol) is obtained from foods in two ways:
performed from animal food sources and derived from beta-carotene in plant
foods. Vitamin A supplements, whether in the form of beta-carotene or retinol,
have not been shown to lower cancer risk, and high-dose supplements may be
toxic. Long-term use of high-dose supplements
increases the risk for lung cancer, particularly amongst people at high risk
such as smokers.
Vitamin C
Vitamin C is found in many vegetables and fruits. Many experimental studies have linked the consumption of foods rich in vitamin C to a reduced risk for cancer. However, the few studies in which vitamin C
has been given as a supplement have not shown a reduced risk for cancer. High doses of vitamin C (more than
2000mg/day) can cause a number of side effects such as headaches, diarrhea,
nausea, heartburn, stomach cramps, and possibly kidney stones.
Vitamin E
Vitamin E is an antioxidant
found in foods such as whole grains, seeds, nuts, and vegetable oils. Studies of
vitamin E supplementation and cancer risk have shown inconsistent results
(positive effects and no effects). High doses of vitamin E supplements can
cause certain side effects and should be avoided.
