Vitamin D and breast cancer.

Do low levels of vitamin D increase my risk of breast cancer? 

Most, but not all, human population studies have found that a low level of vitamin D is associated with increased breast cancer risk and suggest a protective relationship between high levels of vitamin D and breast cancer.

In addition, studies of breast cancer and vitamin D have also shown that increased sunlight exposure is linked to reduced breast cancer incidence as well as breast cancer mortality.

Key facts about vitamin D and breast cancer risk.

• Most studies have found low levels of vitamin D are linked to an increased breast cancer risk.
• The body produces adequate levels of vitamin D if the skin is exposed to sufficient sunlight. Other sources include diet or supplements.
• Despite the association, studies have not shown that taking vitamin D supplements reduces breast cancer risk. Although taking them can restore serum vitamin D levels to a healthy state and are recommended for people unable to achieve sufficient levels through sunshine and diet alone.
• The main function of vitamin D is maintaining calcium levels.
• Vitamin D may help prevent breast cancer by reducing breast cell growth and the production of oestrogen in the body, although more research is needed.

How could vitamin D protect against breast cancer?

Vitamin D may affect breast cancer development through several mechanisms of action. Among other things, it controls normal breast cell growth, reduces cancer cell growth and has anti-inflammatory effects. It can also decrease the conversion of androgens (male hormones) to oestrogens, reducing serum oestrogen levels. High oestrogen levels are associated with an increased risk of breast cancer.

Do vitamin D supplements reduce breast cancer risk?

Despite a link between low levels of vitamin D and increased breast cancer risk, most studies do not demonstrate that taking vitamin D supplements reduces breast cancer risk.  The reasons for this are unclear, and more studies are needed to confirm this finding.

What is a healthy level of vitamin D?

Your vitamin D level depends on many factors, such as how much time you spend outdoors, what you eat, what medications you take, but also your age and skin type.

Most people in the northern hemisphere can make enough vitamin D from daily sun exposure with their forearms, hands or lower legs uncovered (without sunscreen) from late March to the end of September.  For example, fair-skinned types need 10-15 minutes; for darker skin types, 25-40 minutes is recommended.

Vitamin D is stored by the body and helps maintain adequate levels in winter. A diet which contains eggs or oily fish, such as salmon or herring, can provide small amounts of vitamin D.

Start your prevention journey today.

Try one of our recommendations below to boost your vitamin D levels:

• Soak up the sun: Spend 10-25 minutes (depending on your skin type) outside in the midday sun a few times a week, however, ensure your skin doesn’t become sunburnt.
• Eat vitamin D-rich foods: Add oily fish (like salmon and mackerel), egg yolks, and fortified foods (like fat spreads or cereal) to your diet.

Each small action builds momentum. Start today to build a healthier, stronger you for tomorrow.

Further reading

For more information, read our Vitamin D and Breast Cancer science review.  

Last review: Apr-21 | Next review: Apr-24.