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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Breast cancer

woman looking out window

Summary

Breast cancer is a malignant tumor, which is caused by a group of cancerous cells growing in the breast and into other areas around it. The stage of breast cancer depends on the size of the tumor, and if it has spread to other parts of the body.

There are many things that can increase your chances of developing breast cancer. There are some things that you can’t change, like being female, and some things that you can change, like your weight or using birth control. It is a combination of both genetics and lifestyle factors that increase your risk of developing breast cancer.

While it is known that there are many things that can increase your chances for getting breast cancer, researchers still don’t know exactly what causes breast cancer and causes cells to become cancerous.

Studies have shown that there is a link between vitamin D and breast cancer. Women who have breast cancer tend to have low levels of vitamin D in their body. Women with higher vitamin D levels are less likely to develop breast cancer. Women with higher vitamin D levels who already have breast cancer tend to have smaller tumors and are less likely to die from breast cancer.

However, because most studies done so far are observational, researchers can’t say for sure whether low vitamin D levels cause breast cancer or lead to worse outcomes, and therefore whether or not vitamin D can help to prevent or treat breast cancer.

If you have breast cancer or you are trying to prevent breast cancer and want to take vitamin D, it is unlikely to make your breast cancer worse or cause you any harm, as long as you take less than 10,000 IU per day. However, it’s not proven that you will have a better outcome if you have breast cancer. It’s also not proven if taking vitamin D will help you prevent breast cancer.

If you have breast cancer, you shouldn’t take vitamin D in place of your treatment medications. Talk to your physician for more advice about taking supplements.

What is breast cancer?

Breast cancer is a malignant tumor, which is a group of cancerous cells that grow into other areas around it. Breast cancer starts in the cells of the breast, but can spread to other areas of the body, which is called metastasizing. Tumors are made when there is a buildup of unneeded, old, or damaged cells and they form a mass, which then becomes a tumor.

The most common type of breast cancer starts in cells in the breast ducts. Breast ducts are the tubes that carry breast milk.

Tumors in the breast can either be benign or malignant. Benign tumors or lumps are usually not harmful, whereas malignant tumors are cancerous and can spread to other body parts. When breast cancer cells spread, they usually first spread to your underarms and above the collarbone, to small organs called lymph nodes.

The stage of breast cancer depends on the size of the tumor, and whether or not it has spread to other parts of the body. A cancer that is Stage I is early-stage breast cancer, whereas a cancer that is Stage IV is advanced cancer that has spread to other parts of the body1.

How common is breast cancer?

Breast cancer is the second most common cancer among women in the United States. About 1 in 8 women will develop breast cancer in their lifetime. Breast cancer occurs almost entirely in women, but men are able to get it, too. White women have the highest chances of getting breast cancer1,2.

There are many things that can increase your chances for developing breast cancer. There are some things you can’t change, which include:

  • Gender. Being female is the main factor that increases your chances of developing breast cancer.
  • Age. The risk of developing breast cancer increases as you get older.
  • Genetics. Some breast cancers are thought to be related to having unusual forms of some genes.
  • Family history of breast cancer. If you have someone in your extended family that has breast cancer, you are more likely to get it.
  • Race and ethnicity. White women are more likely to develop breast cancer.
  • Women who began menstruation early (before age 12).

There are also some things related to your lifestyle choices that can increase your chances of developing breast cancer. These include3:

  • Having no children or not breastfeeding your children. Pregnancy and breastfeeding reduce the number of menstrual cycles in a woman’s life, which may lower your risk of breast cancer.
  • Long-term birth control. Women who use oral birth control pills for most of their life have a slightly higher chance of developing breast cancer.
  • Using combined hormone therapy with both estrogen and progesterone for over 2 years.
  • Drinking 2 to 5 alcoholic drinks per day.
  • Being overweight or obese.
  • Not getting enough exercise.
  • Long-term smoking or exposure to secondhand smoke.

What causes breast cancer?

While it is known that there are many things that can increase your chances for developing breast cancer, researchers still don’t know exactly what causes breast cancer and causes cells to become cancerous. Hormones are thought to play a large role in breast cancer, but it is not fully understood how or why.

Another example is that some people might have changes in their DNA which causes them to have more genes called oncogenes, which cause cells to divide faster and make tumors.

While it is known that there are many things that can increase your chances for developing breast cancer, researchers still don’t know exactly what causes breast cancer and causes cells to become cancerous.

Researchers do know that cancers come from strange changes in cells and genes. For example, genes called tumor suppressor genes can slow cells from growing into cancerous cells. When people have altered versions of these genes, they don’t slow the cancer cell growth, so breast cancer is more likely to develop.

Another example is that some people might have changes in their DNA which causes them to have more genes called oncogenes, which cause cells to divide faster and make tumors.

Sometimes you can develop these DNA changes over time, rather than be born with them. Researchers think that being exposed to radiation or chemicals may cause DNA changes over time and cause cancer, but they don’t know for sure.

Since there are risk factors that you can’t change, like age and gender, and risk factors you can change, like your weight or using birth control, it’s clear that a combination of both genetics and environmental (lifestyle) factors causes breast cancer3.

What is the link between breast cancer and vitamin D?

Many studies have shown that there is a link between vitamin D and breast cancer. Women who have breast cancer tend to have low levels of vitamin D in their body.

Researchers have found how vitamin D might have a role in breast cancer.  Vitamin D receptors are found on the surface of a cell where they receive chemical signals. By attaching themselves to a receptor, these chemical signals direct a cell to do something, for example to act in a certain way, or to divide or die.

There are vitamin D receptors in breast tissue, and vitamin D can bind to these receptors. This can cause cells like oncogenes to die or stop growing, and can stop the cancer cells from spreading to other parts of the body.  Therefore, it is thought that vitamin D may help in protecting against breast cancer, by making cells in the breast smarter.

However, the relationship between breast cancer and vitamin D is complex, not fully understood, and is still being studied4,5,6.

What does the research say in general about vitamin D and breast cancer?

Preventing breast cancer

Some studies have been done which have found that women with low levels of vitamin D are more likely to develop breast cancer.

Some studies have been done which have found that women with low levels of vitamin D are more likely to develop breast cancer.  A recent review of many studies found that post-menopausal women with low levels of vitamin D had a higher risk of getting breast cancer compared to post-menopausal women with high levels of vitamin D.

Other studies have found what is called a dose-response relationship, where for each increase in vitamin D levels in the body, there is a decrease in breast cancer risk5.

However, most prevention studies on vitamin D and breast cancer have been observational, meaning that researchers can’t say for sure whether vitamin D prevents breast cancer or not.

Treating breast cancer

No studies have been done about treating breast cancer patients with vitamin D. Some studies have shown that there is a link between vitamin D levels and recurrence of breast cancer, tumor size, and death from breast cancer. This means that having enough vitamin D may be able to help keep a cancer from getting worse.

In a review of many studies, researchers found that women with breast cancer who had low vitamin D levels had a more than doubled risk of their cancer coming back, and an almost doubled risk of death compared to women with high vitamin D levels.

The studies that were reviewed were observational, which means that the researchers can’t say for sure if low vitamin D levels caused breast cancer to come back4.

What does recent research say?

Preventing breast cancer

There is a growing amount of recent research that shows a link between vitamin D levels and risk of developing breast cancer, meaning that getting enough vitamin D may have a protective effect in helping to prevent breast cancer.

A study done in 2013 in the United States7,8 looked at a large group of women who were part of an experiment involving calcium and vitamin D supplements. The women were assigned to either take a calcium (1,000 mg) plus vitamin D (400 IU) supplement or a dummy pill for 7 years. Then the researchers looked at health outcomes almost 5 years later, after the women had stopped taking the pills. They found that:

  • Women who were in the calcium plus vitamin D group had an 18% lower risk of developing early stage breast cancer.

The women took a low dose of vitamin D compared to other studies, and had low vitamin D levels in their body to begin with.  The women were also allowed to take vitamin D or calcium supplements on their own, which could make results hard to interpret. Since the experiment didn’t only look at vitamin D supplements, it’s hard to tell for sure if vitamin D is what lowers cancer risk or if it’s calcium and vitamin D combined.

A paper published in 20139 looked at 9 different studies involving vitamin D levels and the risk of developing breast cancer later in life. They found that:

  • Post-menopausal women with higher vitamin D levels had a 12% lower chance of developing breast cancer than post-menopausal women with low vitamin D levels.
  • There was what is called a threshold effect, meaning that there was no additional decrease in breast cancer risk when the women had vitamin D levels above 35 ng/mL.

Since the review looked at observational studies, researchers can’t say for sure whether or not vitamin D can prevent breast cancer.

An experiment done in 2007 in the United States10 looked at whether taking vitamin D and calcium supplements could lower a woman’s risk of developing cancer after 4 years. A large group of post-menopausal women were assigned to take a calcium supplement, a vitamin D (1,000 IU) plus calcium (1,400-1,500 mg) supplement, or a dummy pill. They found that:

  • Both the calcium-only and the calcium plus vitamin D groups had lower rates of cancer than the dummy pill group after 4 years.
  • Women with higher vitamin D levels had a lower risk of developing cancer.

This study looked at the chance of developing any kind of cancer, not just breast cancer. Since the experiment didn’t only look at vitamin D supplements, it’s hard to tell for sure if vitamin D is what lowers cancer risk, or if it’s calcium and vitamin D combined. Vitamin D and calcium might work together to lower the chances of getting cancer.

Treating breast cancer

A 2012 study done in Belgium11 looked at women with early breast cancer and their vitamin D levels. Five years later, they looked at how their breast cancer had progressed. The researchers found that:

  • Women with low vitamin D levels had bigger tumors than women with high vitamin D levels.
  • Women with low vitamin D levels had an increased risk of death during the study.
  • Post-menopausal women with high vitamin D levels were most likely to have the smallest tumors and lowest chance of death.

This study found many links between breast cancer and vitamin D. However, the researchers can’t say for sure if low vitamin D levels cause worse outcomes in breast cancer, because the study was observational.

A study done in 2009 in Canada12 looked at a group of women who had an early stage of breast cancer. The researchers looked at their vitamin D levels and followed them over 12 years to see how their cancers progressed. They found that:

  • Women with low vitamin D levels were almost twice as likely to have their cancer spread to another part of the body than women with high vitamin D levels.
  • Women with low vitamin D levels were more likely to have died during the study than women with high vitamin D levels.
  • Women with low vitamin D levels had worse tumors than women with high vitamin D levels.

This study looked at many different outcomes that can happen to someone with breast cancer.

Since these studies were observational, we can’t say for sure  whether having a good amount of vitamin D can help lead to better outcomes in breast cancer or not.

Key points from the research

  • Research from many studies has shown that women with breast cancer are more likely to have low levels of vitamin D in their body.
  • Some research has shown that post-menopausal women who don’t get very much vitamin D may be more likely to develop breast cancer later in life.
  • Research has shown that women who have breast cancer are more likely to develop bigger tumors and are more likely to have recurrent breast cancer if they have low levels of vitamin D.
  • Women with higher vitamin D levels are less likely to develop breast cancer and less likely to die from breast cancer.
  • However, due to not enough experimental studies, it’s not possible to say whether low vitamin D levels cause breast cancer or lead to worse outcomes, and therefore whether or not vitamin D can help to prevent or treat breast cancer.
  • Overall, more experiments are needed to give clearer answers about whether taking a vitamin D supplement can prevent or treat breast cancer. These studies are underway.

What does this mean for me?

Research does show that there is a link between vitamin D and breast cancer. Studies have shown that women with low levels of vitamin D are more likely to develop breast cancer.

Studies have also shown that in women who already have breast cancer, low levels of vitamin D are linked to worse outcomes, like bigger tumors, cancer spreading to other body parts, and death.

Research does show that there is a link between vitamin D and breast cancer. However, researchers aren’t sure if vitamin D deficiency causes breast cancer.

Studies have also shown that in women who already have breast cancer, low levels of vitamin D are linked to worse outcomes, like bigger tumors, cancer spreading to other body parts, and death.

However, research hasn’t yet been able to show for sure whether low levels of vitamin D cause breast cancer. Doctors don’t know yet whether taking a vitamin D supplement, or getting more sun exposure, can help to prevent or treat breast cancer.

If you have breast cancer or you are trying to prevent breast cancer and want to take vitamin D, it is unlikely to make your breast cancer worse or cause you any harm, as long as you take less than 10,000 IU per day. However, it’s not proven that you will have a better outcome if you have breast cancer. It’s also not proven if taking vitamin D will help you prevent breast cancer.

If you have breast cancer, you shouldn’t take vitamin D in place of your treatment medications. Talk to your physician for more advice about taking supplements.

References

  1. What You Need to Know About Breast Cancer. National Cancer Institute, 2013. Web. 25 November 2013.  <http://www.cancer.gov/cancertopics/wyntk/breast>
  2. Breast Cancer. Centers for Disease Control and Prevention, 2013. Web. 25 November 2013.  <www.CDC.gov/cancer/breast>
  3. Breast Cancer. American Cancer Society, 2013. 25 November 2013. <http://www.cancer.org/cancer/breastcancer/>
  4. Rose AAN, Elser C, Ennis M, et al. Blood levels of vitamin D and early stage breast cancer prognosis: a systematic review and meta-analysis. Breast Cancer Res Treat 2013;141:331-339.
  5. Wang D, Velez de-la-Paz OI, Zhai JX, et al. Serum 25-hydroxyvitamin D and breast cancer risk: a meta-analysis of prospective studies. Tumor Biol 2013;1-9.
  6. Welsh J. Cellular and molecular effects of vitamin D on carcinogenesis. Arch Biochem Biophys 2012;523(1):107-114.
  7. Chlebowski RT, Johnson KC, Kooperberg C, et al. Calcium plus vitamin D supplementation and the risk of breast cancer. J Natl Cancer Inst 2007;100:1581-1591.
  8. Cauley JA, Chlebowski RT, Wactawski-Wende J, et al. Calcium plus vitamin D supplementation and health outcomes five years after active intervention ended: the Women’s Health Initiative. Journal of Women’s Health 2013;22(11):915-929.
  9. Bauer SR, Hankinson SE, Bertone-Johnson ER, et al. Plasma vitamin D levels, menopause, and risk of brast cancer: dose-response meta-analysis of prospective studies. Medicine 2013;92:123-131.
  10. Lappe JM, Travers-Gustafson D, Davies KM, et al. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr 2007;85:1586-91.
  11. Hatse S, Lambrechts D, Verstuyf A, et al. Vitamin D status at breast cancer diagnosis: correlation with tumor characteristics, disease outcome, and genetic determinants of vitamin D insufficiency. Carcinogenesis 2012;33(7):1319-1326.
  12. Goodwin PJ, Ennis M, Pritchard KI, et al. Prognostic effects of 25-hydroxyvitamin D levels in early breast cancer. J Clin Oncol 2009;27:3757-3763.

This page was last updated December 2013.

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