There is no strong evidence that vitamin D affects the risk or growth rate of any cancer, including breast cancer.
Vitamin D is a fat-soluble vitamin that plays an important role in helping to build and maintain our bones, it also plays a role in helping to support our immune system.
Vitamin D is one of the few vitamins that our body can make itself, it’s formed in the body when the skin is exposed to sunlight. It’s important to still stay safe in the sun as too much sun exposure can cause skin cancer and sunburn.
Vitamin D can also be found in certain foods such as oily fish, liver, eggs and fortified cereals and spreads. However, it may not always be possible to get enough vitamin D from sunlight and diet.
It’s recommended that people in the UK consider taking a supplement of 10μg (micrograms) of vitamin D a day in the autumn and winter (even on a sunny winter’s day, our body can’t produce much vitamin D). In certain situations, you may be advised to take a 10μg supplement of vitamin D all year round.
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 by a blood test carried out by your doctor. If you are found to be deficient or low in vitamin D, you may need to take a vitamin D supplement. Your doctor or a dietitian will be able to advise what dosage of supplement you need to take.
You can find out more about vitamin D at:
In autumn 2022, we published our review of evidence on how a woman’s risk of dying after a breast cancer diagnosis is affected by her weight, diet and physical activity. Read about the findings