Vitamin D Deficiency and Breast Cancer

Research suggests that women with vitamin d deficiency have a higher risk of developing breast cancer.

Research suggests that women with vitamin D deficiency have a higher risk of developing breast cancer. Vitamin D may also play a role in controlling normal breast cell growth and may be able to stop breast cancer cells from growing.

You likely know that vitamin D helps the body absorb calcium, which is essential for good bone health. Vitamin D also helps the immune, muscle, and nervous systems function properly. Most vitamin D is made when an inactive form of the nutrient is activated in your skin as it gets exposed to sunlight. Smaller amounts of vitamin D are found in fortified milk, breads and cereals, and in fatty fish and eggs. As more and more people spend most of their time out of direct sunlight or wearing sunscreen when they are in the sun, vitamin D production from sun exposure is limited and women are increasingly becoming vitamin D deficient.

A study published in the journal Endocrinology used mice to explore the relationship between vitamin D and breast cancer. The study noted that patients with breast cancer frequently have preexisting vitamin D deficiency when their cancer develops, and researchers sought to learn whether this was coincidental or if low levels of vitamin D contributed to the development of cancer.

The two most reliable ways to boost your vitamin D level are to get more direct sunlight exposure and take vitamin D3 supplements. Eating foods rich in vitamin D can help, but is less effective.

Sun Exposure

Even short periods of direct peak sun exposure — 15 minutes 3 times a week, for example — can give you a healthy dose of vitamin D. It’s also impossible to overdose on vitamin D from the sun. While sun exposure offers vitamin D benefits, it does have risks. Sun exposure increases your risk of skin cancer, including melanoma, the most dangerous type.

There are many variables that can affect how much vitamin D you’ll actually produce from sunlight:

  • The darker your skin color, the less vitamin D you produce.
  • The farther you live from the equator, the less vitamin D you produce.
  • Fewer daylight hours mean you produce less vitamin D.

All these factors can make it difficult to get enough vitamin D from sun exposure alone.


Before you adjust your vitamin D intake, it’s important to know your vitamin D serum level. This is done with a simple blood test that your doctor can order for you when you’re in for a routine physical. Vitamin D researchers recommend a serum level of 40-60 ng/ml (nanograms/milliliter).

Also be sure to talk with your doctor about your serum levels and which supplements would be best for you. If your level is low, once you’ve been taking a supplement to get back into the normal range, have your vitamin D level checked again in a few months and adjust your supplement dose accordingly. Taking too much vitamin D occasionally can cause you to have too much calcium in your blood. When choosing a vitamin D supplement, most experts recommend taking the D3 form of the vitamin, not the D2 form.



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