Vitamins, diet supplements and cancer

Vitamins, minerals, essential fats and amino acids are important nutrients for our bodies. Eating a varied amount of these nutrients gives us energy and helps our bodies to grow and repair. 


  • Try to eat a balanced diet with plenty of fresh fruit and vegetables. 
  • Low levels of nutrients can make you feel ill.
  • Use supplements under the supervision of your medical team and a dietitian.

What are vitamins, minerals and other nutrients?

A balanced and varied diet is the best way to get a healthy supply of vitamins and minerals. Some examples of these various nutrients are:

  • vitamins A, C, D and E
  • minerals – like zinc, calcium, selenium and magnesium
  • essential fats
  • essential amino acids – like phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine, and lyseine
  • some plant compounds (phyto nutrients or botanicals) – like carotenoids, flavonoids, and isoflavones

You might find that your cancer or your cancer treatment makes it difficult to eat or drink properly. Or your cancer might stop you absorbing some nutrients from your food or drink. So you might have low levels of particular nutrients. This can make you feel unwell. 

Why people with cancer use dietary supplements

Dietary supplements are also called nutritional supplements. 

You might need to have dietary supplements if you have low levels of certain nutrients. Some hormone treatments for breast and prostate cancer can weaken your bones. So your doctor might prescribe calcium and Vitamin D to protect your bones.

Or, your cancer might stop you from easily absorbing nutrients from your food. So your doctor might prescribe a daily multivitamin and mineral supplement.

Most people use supplements alongside their cancer treatments, such as radiotherapy or chemotherapy. But others choose to use them instead of conventional treatments.

Taking dietary supplements instead of conventional cancer treatment could harm your health. It might reduce the chance of curing or controlling your cancer.

It is important to talk to a health professional if you're thinking of taking nutritional supplements. They can refer you to a dietitian. They can given advice on diet and supplements. 

How you have it

Vitamins and dietary supplements come as pills, tablets or a liquid. Some complementary or alternative therapists also use injections of dietary supplements.

Side effects

Some vitamins or minerals could interfere with how well cancer drugs work. Antioxidant supplements such as co enzyme Q10, selenium and the vitamins A, C and E can help to prevent cell damage. But there is some evidence that taking high dose antioxidant supplements during cancer treatment might make the treatment less effective. 

Get advice from your doctor, specialist nurse or dietitian if you want to take supplements and are having any kind of cancer treatment. 

Research into dietary supplements and cancer

There is no reliable evidence that any dietary supplement can help to prevent cancer. Some research has found that taking certain supplements could increase the risk of some cancers developing.

There is evidence that a healthy diet with plenty of fruit and vegetables can reduce your cancer risk.

Research has looked at whether certain vitamins and supplements can help to prevent cancer in certain groups of people.

A study looked at vitamin D supplements in preventing cancer and heart disease. The researchers found that vitamin D supplements did not lower the incidence of cancer or heart disease. 

An organisation called The Cochrane Collaboration carries out systematic reviews. These are overviews of all the research into a specific issue. The reviews look at the published results of all the trials that have investigated a certain treatment in a particular situation. They pull all that information together and draw conclusions.

A Cochrane review published in 2018 looked at an essential mineral called selenium. They wanted to see if selenium supplements could reduce cancer risk. After looking at all the information they found that selenium did not reduce cancer risk. Some of the trials reported a higher incidence of high grade prostate cancer and type 2 diabetes in people who took selenium supplements. 

How much it costs

Supplements can vary in their price. Some may cost from around £5 to £30 from health food shops. Other supplements can cost a lot more. It's important to check with your specialist or dietitian before you start taking any supplements. 

A word of caution

There is no reliable evidence that dietary or nutritional supplements can prevent, cure or control the growth of cancer. Check with your specialist before you take any supplements to make sure they won't interfere with any cancer treatment you are having. 

More information about vitamins and minerals

MedlinePlus in the USA has information about vitamins and minerals used as dietary supplements. They provide information about possible side effects and research about vitamins and cancer.

  • Selenium for preventing cancer
    M. Vineti and others.
    Cochrane Systematic Review, January 2018.

  • Vitamin D supplements and prevention of cancer and cardiovascular disease
    J.E.Manson and others
    New England Journal of Medicine, 2019. 380;33-34

  • The Vitamin epidemic: what is the evidence for harm or value?
    M. Kennedy
    Internal Medicine Journal, Royal Australian College of Physicians, 2018, Vol 48, 901-907

  • Drugs for preventing lung cancer in healthy people
    M Cortés-Jofré and others
    Cochrane Database of Systematic Reviews, March 2020. 

  • A systematic review on the role of fish oil for the treatment of cachexia in advanced cancer: an EPCRC cachexia guidelines project
    A Ries and others
    Palliative Medicine, 2012. Volume 26, Issue 4

  • Improved survival in patients with end-stage cancer treated with co enzyme Q10 and other antioxidants: a pilot study
    N Hertz and RE Lister
    Journal of International Medical Research, 2009. Volume 37, Issue 6

Last reviewed: 
22 Apr 2022
Next review due: 
22 Apr 2025

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