Do not use supplements for cancer prevention
Aim to meet nutritional needs through diet alone and avoid supplement use
On this page
Overview of evidence
There is strong evidence from randomised controlled trials that high-dose beta-carotene supplements may increase the risk of lung cancer in some people.
There is no strong evidence that dietary supplements, apart from calcium for colorectal cancer, can reduce cancer risk.
Goal
- High-dose dietary supplements are not recommended for cancer prevention – aim to meet nutritional needs through diet alone.
A dietary supplement is a product (usually in pill or powder form) that contains a ‘dietary ingredient’ intended to achieve levels of consumption of micronutrients (vitamins, minerals, and trace elements) in doses far greater than those absorbed from food in any typical diet.
This Recommendation applies to all doses and formulations of supplements, unless they have been advised by a qualified health professional who can assess potential risks and benefits.
The Panel reviewed the published evidence related to a range of supplements, those that are specifically named within this recommendation were found to have strong evidence related to their impact on cancer prevention.
Evidence
Randomised controlled trials of high-dose supplements have not demonstrated the same protective effects of micronutrients on cancer risk suggested by observational epidemiology. Furthermore, some trials have shown that supplements have the potential to bring about unexpected adverse effects.
There is convincing evidence that:
- Consuming high-dose beta-carotene in supplements INCREASES the risk of lung cancer (in people who smoke or used to smoke tobacco).
- Beta-carotene belongs to a group of coloured pigments called carotenoids, found in many fruits and vegetables. It’s converted to vitamin A in the body.
- Consuming beta-carotene in supplements is unlikely to have a substantial effect on the risk of prostate cancer.
- Consuming beta-carotene in supplements is unlikely to have substantial effect on the risk of skin cancer (non-melanoma).
There is probable evidence that:
- Consuming calcium supplements DECREASES the risk of colorectal cancer. However, overall, it’s best to eat a healthy diet rather than rely on dietary supplements to protect against cancer.
Additional information
Vitamins are organic molecules (either fat or water soluble) needed for metabolism. Most cannot be made in the body and so must be supplied in the diet.
- Vitamins A (retinol), D, E and K are fat soluble and can only be digested, absorbed and transported in conjunction with fats. They are found in liver, egg yolk and oily fish, and in the fat in milk and dairy products, animal fats, and vegetable oils.
- Fat soluble vitamins are stored in the liver and in body fat. For this reason, they do not need to be consumed every day. Continuous high intakes, especially of retinol and vitamin D, can lead to excess accumulation and toxicity.
- Vitamin C and the B vitamins are water soluble. The B group includes thiamin (vitamin B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9) and cobalamin (B12).
- Excess amounts of water-soluble vitamins are generally not toxic because they are excreted in urine rather than stored in the body. This also means that they generally have to be consumed more frequently than fat-soluble vitamins.
- Foods of plant origin are important sources of water-soluble vitamins. For example, grains, vegetables, fruit, some roots/tubers, and pulses. They can be destroyed by heat or exposure to the air, or lost by leaching during cooking (eg when vegetables are boiled).
Mechanisms
Beta-carotene and lung cancer
Evidence from 2-3 intervention trials showed that high-dose beta-carotene supplements increase the risk of lung cancer among people who smoke/used to smoke. These findings contrast with epidemiologic studies on dietary-derived circulating beta-carotene levels. These generally report a decreased risk of lung cancer, thought to be because carotenoids can block certain carcinogenic processes and inhibit tumour cell growth.
The mechanisms underlying the effect of high dose beta-carotene supplementation on lung cancer risk are complex and not yet fully understood, but may in part be due to the interaction/binding of smoke particles with DNA. Tobacco smoke may also disrupt cellular processes and signalling pathways, leading to the potential for cancer development.
Overall, it appears that there’s a dose-response effect for beta-carotene. This may explain the apparent paradoxical elevation of lung cancer incidence among people who smoke and who take high-dose beta-carotene supplements.
Calcium and colorectal cancer
A long-standing mechanism proposed for calcium and its potential activity against colorectal cancer development is the ability of calcium to bind unconjugated bile acids and free fatty acids, diminishing their toxic effects on the colorectum.
More recent cell culture studies suggest that it may also reduce cancer cell proliferation and promote cell differentiation, likely by influencing different cell-signalling pathways.
Implications for other diseases
For most people, consumption of the right food and drink is more likely to protect against cancer than consumption of dietary supplements. However, supplements may at times be beneficial for specific population groups:
- Vitamin B12 for people over the age of 50 who have difficulty absorbing naturally occurring vitamin B12.
- Iron and folic acid supplements for people with anaemia and women who may become or are pregnant.
- Vitamin D supplements for infants and young children, pregnant and breastfeeding women and people with limited exposure to the sun or who have darker skin and live in regions with limited sunshine.
Public health / policy implications
In many parts of the world, nutritional inadequacy is endemic. In crisis situations it is necessary to supply supplements of nutrients to such populations or to fortify food to ensure at least minimum adequacy of nutritional status. The best approach is to protect or improve local food systems so that they are nutritionally adequate and promote healthy diets.
This also applies in high-income countries, where impoverished communities and families, and vulnerable people, including those living alone, the elderly, and the chronically ill or infirm, may also be consuming nutritionally inadequate diets. In such cases of immediate need, supplementation is necessary.
Policymakers should aim to maximise the proportion of the population achieving nutritional adequacy without dietary supplements by implementing policies that create a healthy food environment and food system. Policymakers are encouraged to frame specific goals and actions according to their national context