Vitamin D is a fat-soluble vitamin that plays an important role in helping build and maintain bones and immune function. Vitamin D is one of the few vitamins that our body can make itself. Vitamin D is formed in the body when the skin is exposed to sunlight. It is important to still stay safe in the sun as too much sunlight can cause skin cancer and sunburn. Small amounts of Vitamin D can be found in foods such as oily fish, red meat, eggs and fortified cereals and spreads. It may not always be possible to get enough Vitamin D from sunlight and diet. Public Health England recommends that people in the UK should consider taking a supplement of 10μg Vitamin D a day in the autumn and winter.

There isn’t any strong evidence that vitamin D increases the risk of developing cancer or affects the growth rate of any cancer, including prostate cancer.

However vitamin D is important for men having hormone therapy for prostate cancer because of the risk of bone thinning.

Other risk factors for having low levels of Vitamin D include being older, being housebound or spending a lot of time inside, those who wear clothes that cover most of their skin and those with dark skin from African, Afro-Caribbean or South Asian backgrounds.

Vitamin D levels can be easily checked using a blood test carried out by your doctor. If you are found to be deficient in Vitamin D then you will need to take a higher dose of Vitamin D. You will be told how much to take by your doctor or dietitian.

No. There are no benefits from taking dietary supplements during cancer treatment. If you eat and drink a balanced diet, you will get enough vitamins and minerals. There can be risks if you take dietary supplements during treatment. Vitamin and mineral supplements can reduce the effect of radiation and chemotherapy.

We recommend that you only take supplements if you are deficient in vitamins and / or minerals. Always choose a supplement with up to 100% of the Recommended Daily Allowance (RDA). If you want to use dietary supplements during radiation or chemotherapy, always discuss this with your doctor and dietitian first.

What are dietary supplements?
Dietary supplements are intended as a supplement to the daily diet and contain vitamins, minerals or certain bioactive substances. Dietary supplements come in the form of pills, powders, drops, capsules or drinks. Sometimes they contain one substance, such as vitamin C, and sometimes a combination of substances such as a multivitamin supplement.

What does research show?
Some side effects from cancer treatments may be reduced by taking supplements. Supplements of vitamins and minerals can also have a bad effect such as increasing the growth or number of tumours.

Supplements can also react with the medical treatments for cancer. Patients who take large amounts of vitamins are more likely to suffer from unwanted, toxic effects during treatment. A number of scientific studies have shown that taking supplements reduced how well a treatment worked. Other studies showed that patients taking supplements had a lower survival rate than patients who did not take supplements.

Our advice
If you have a poor appetite or are unable to eat a healthy diet due to cancer or the side effects of your treatment then you might be deficient in some vitamins and minerals. If you are worried then it’s important to talk about your diet with a doctor or dietician. A dietitian will be able to tell you if you should be taking supplements.

If you have low levels of vitamins or minerals in your diet taking a supplement for a while can be a good addition to your diet. Always choose a supplement with up to 100% of the Recommended Daily Allowance (RDA).

If your diet improves or you are told by your doctor to use special nutrition that is high in vitamins and minerals you can talk to your doctor or dietitian about stopping supplements. Some patients receive special nutrition via a tube or liquid drink.