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, most people do not need dietary supplements if they eat a wide variety of nutritious foods.

Cancer Council recommends people eat a variety of nutritious foods, especially fruit and vegetables, instead of individual nutrients in supplement form.

Supplements versus whole foods

Foods like fruit and vegetables contain lots of nutrients, but also many other beneficial substances such as fibre, minerals and antioxidants. Dietary fibre 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 better than relying on supplements.

Research has shown that nutrients 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 nutrient may be due to interactions between different food compounds that don’t occur when nutrients are isolated in a supplement.

Eating plenty of nutritious foods like fruit and vegetables, legumes, nuts and wholegrains can also help you to maintain a healthy body weight.

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) is best when it comes to lowering the risk of cancer. There are likely to be important, but not yet identified, components of whole food that are not included in supplements.

Currently the only evidence to suggest that supplements (e.g. tablets, capsules) can reduce cancer risk is for calcium supplements. There is probable evidence  that taking calcium supplements of more than 200 mg per day protects against bowel cancer.

Calcium

Calcium is a mineral that is the main constituent of bones and teeth. Calcium has many functions in the body, including nerve and muscle activity, cell differentiation and proliferation. The main source of calcium in Australian diets is dairy foods, but there are smaller amounts in leafy greens, legumes and nuts, and fish with edible bones.

There is probable evidence that taking calcium supplements of more than 200 mg per day protects against bowel cancer.

Beta-carotene

Beta-carotene is the orange colour 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, taking high-dose beta-carotene supplements (20 mg per day or more) is a cause of lung cancer in people who smoke cigarettes or used to smoke.

Cancer Council recommends people avoid taking high doses (>20 mg) of beta-carotene supplements, especially if they smoke.