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. Choosing to stop conventional treatment recommended by your doctor could reduce the chance of curing or controlling your cancer.

Check with a pharmacist or your healthcare team before taking any supplements. Some of these could interfere with how well cancer drugs work. Supplements at a high dose could be toxic or harmful to your health..

If possible, it’s better to have a balanced diet with a variety of food (rather than a supplement).

How you have them

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. 

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. 

Individual supplements and vitamins

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. 


Bromelain is a natural enzyme found in pineapples.

Laboratory and animal studies showed that bromelain might reduce inflammation. Researchers used it in studies of patients with:

  • burn and skin conditions
  • diarrhoea
  • osteoporosis
  • osteoarthritis

Animal studies showed that bromelain might prevent or treat certain cancers. And that it might stop them from growing. Bromelain might also be used alongside other cancer treatments.

But we need more research and better quality studies before doctors can use bromelain to prevent or cure cancer.


Essiac is a herbal remedy from Canada. It is a mixture of roots, bark and leaves that you boil to make a drinkable liquid. Or you can buy it as capsules or drops. You can also buy a modified version of Essiac, which is called Flor Essence.

People use Essiac because they believe it can:

  • cure or control their cancer
  • boost their immune system
  • help them to feel better

Several studies and reviews found that Essiac had no anti cancer effects. Essiac may cause nausea and vomiting. Other side effects were also reported.


Laetrile is a man made (synthetic) form of the natural substance amygdalin. Amygdalin is a plant substance found in apricot and cherry seeds, raw nuts and bitter almonds.

Some people call laetrile vitamin B17, although it isn’t a vitamin.

People who use laetrile believe it might:

  • improve their health, energy levels and wellbeing
  • detoxify and cleanse the body
  • help them to live longer

When the body processes laetrile, it changes to cyanide. Cyanide is a type of poison which is thought to kill cancer cells. But there is no reliable scientific evidence to show that laetrile or amygdalin can treat cancer. Despite this, it still gets promoted as an alternative cancer treatment.

Laetrile can cause serious side effects and liver damage. Because of this, the sale of laetrile is not allowed in the UK.


Turmeric is a spice grown in many Asian countries. It belongs to the ginger family and is the main ingredient of curry powder.

The main active ingredient in turmeric is curcumin or diferuloyl methane. Laboratory studies have shown curcumin seems to be able to kill cancer cells and prevent more from growing. 

There have been some clinical trials looking at curcumin in people with colorectal cancer, prostate cancer and other cancer types. The studies were small and there were limitations to the trials. At the moment, there is no clear evidence in humans to show that turmeric or curcumin can prevent or treat cancer.

People have reported stomach pain when eating too much turmeric.


Isoflavones are chemicals in soy products that are known for their health benefits. It is very similar to the hormone oestrogen. Oestrogen can stimulate some cancers, such as breast cancer, to grow. People often worry that foods or soy supplements containing isoflavones might have the same effect as oestrogen and cause cancer to grow. But current research says that foods containing natural isoflavones are safe. Early studies also show that isoflavones may have some benefits in certain cancers. It may:

  • protect against cancer
  • reduce inflammation
  • reduce damage to cells
  • help DNA to repair

In breast and prostate cancer isoflavones may reduce the risk of cancer coming back. This is because isoflavones are similar to the hormone oestrogen and bind to the oestrogen receptors on cells. By doing so, it blocks cancer cells from absorbing oestrogen. However, these studies are based on Asian diets that contain large amounts of soy.

Soy can be a meat free source of protein and fibre in your diet. Healthcare professionals don’t recommend the use of soy supplements to protect against cancer.


One trial showed that selenium might protect against the overall risk of prostate cancer in men with a history of non melanoma skin cancer. But a later systematic review found that selenium supplements had no benefit in protecting against cancer.

Some randomised controlled trials showed a higher incidence of high grade prostate cancer and type 2 diabetes in people taking selenium supplements.

Research in this area has produced mixed results. Doctors don't recommend that people take it to treat cancer or reduce the risk of cancer.

Vitamin C

People often take vitamin C in much higher doses than the recommended nutrient intake (RNI) of 40mg per day. Some people take it as a drip into the bloodstream (IV). 

There is no good quality research to say that vitamin C helps chemotherapy to work better or help to reduce its side effects. 

High doses of vitamin C can cause side effects such as an upset stomach or kidney stones.

Vitamin D

Research continues to look at the role of vitamin D in the development and recurrence of different cancers. Some early studies suggest that there is a link between low levels of vitamin D and the development of cancer. But due to the lack of firm evidence, health professionals don’t recommend people take vitamin D supplements to reduce their risk of cancer coming back.

However, vitamin D is important for keeping our bones healthy. We need it to absorb calcium. Most of our vitamin D comes from sunlight, but some comes from our diet.

The Government recommends that all people in the UK consider take 10 micrograms of vitamin D in the autumn and winter. Some adults at risk of vitamin D deficiency are recommended to take a supplement throughout the year. Check with your healthcare team or GP if you think you should be taking vitamin D supplements. 

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.

  • 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

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. If you need additional references for this information please contact with details of the particular issue you are interested in.

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

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