I have breast cancer. Should I take vitamin D?
The answer is a resounding YES, not only because there are positive clinical trials showing that vitamin D prolongs life, but also because there are so many studies showing that it helps the pathological process. It will take decades to complete studies showing whether vitamin D increases overall cancer survival, but such studies are underway. In the meantime, most studies show that vitamin D helps with both cancer survival and prevention.
If you have breast cancer or you are trying to prevent breast cancer and want to take vitamin D, it is highly unlikely vitamin D supplementation will make your breast cancer worse or cause you any harm, assuming you take less than 20,000 IU per day. To help prevent breast cancer, women should achieve vitamin D blood levels of at least 60 ng/ml in the blood. This usually requires supplementation of 5,000 to 10,000 IU per day of vitamin D. After taking vitamin D for several months, obtain a blood vitamin D level to see if you are above 60 ng/ml.
If you currently have breast cancer, we recommend that you get your vitamin D blood level above 70 ng/ml. This will require anywhere from 5,000 to 15,000 IU/day. Make sure you check your vitamin D blood level after taking vitamin D for several months. Our low-cost in-home vitamin D blood test is an ideal way to monitor your vitamin D levels.
If you take vitamin D either because you want to help prevent breast cancer or help treat it, you will never know if it helped. By its very nature, breast cancer is highly variable. So, if you take vitamin D to help prevent it, you may still get it. But without the vitamin D you may have developed it five years earlier. The same is true of treatment; if it recurs, you can’t know if vitamin D didn’t help or if it would have recurred earlier without vitamin D. It is impossible to know what did not happen.
A number of studies show that vitamin D helps. For example, a 2017 study found that breast cancer patients undergoing chemotherapy were almost three times more likely to have a “complete pathologic response” if they had high vitamin D blood levels. This meant that women with higher vitamin D levels were much more likely to have “no residual invasive disease in breast and lymph nodes,” after chemotherapy compared to women with low vitamin D levels. Do you see why we recommend vitamin D? For a more detailed analysis of the study, see our blog.
Another 2017 study found that lower vitamin D levels in women with breast cancer was associated with increased tumor grade, more locally advanced and metastatic disease, more positive lymph nodes and a lower proportion of estrogen and progesterone positive tumors, all of which indicate more serious prognostic findings. For a more detailed analysis of the study, see our blog.
What about women with breast cancer who took vitamin D? Does vitamin D improve their disease-free survival? Disease-free survival is the length of time after primary treatment for that cancer ends that the patient survives without any signs or symptoms of that particular cancer. Another study found that women with HER(+) breast cancer had a much better disease-free survival rate if they took vitamin D. The women only took about 1,000 IU/day, which is a small amount, and the results may well have been better with a larger dose. See our blog for our detailed analysis of the Zeichner study.
When scientists combine many studies to look at the results of the combined studies, this is called a meta-analysis, the strongest proof in medicine. Another study combined eight studies to see if higher vitamin D blood levels improved survival. Here’s what they found:
- Women who have had breast cancer and are vitamin D deficient are >two times more likely to experience a breast cancer recurrence.
- Studies that looked at breast cancer deaths found that vitamin D deficiency was associated with increased risk of death.
- When pooled together, study results showed that a woman with breast cancer was twice as likely to die if she was vitamin D deficient.
- For our detailed analysis of the above studies, see our blog.
The results of the above (and other) studies are why we recommend that breast cancer patients either take vitamin D or, if possible, sunbathe. It is possible that science will eventually find that the above studies are wrong, and that vitamin D does not help with breast cancer treatment. For that reason, some scientists (usually men) conclude that women with breast cancer should not take vitamin D until science proves, beyond a reasonable doubt, that vitamin D helps with the treatment of breast cancer.
That makes no sense to us, because the studies to date indicate that vitamin D does help and because vitamin D is incredibly safe. For example, in the last 15 years Poison Control reported 25,397 vitamin D overdoses. But not one of those people died and only three developed vitamin D toxicity. How many hundreds of thousands of women died of breast cancer during that same 15-year period?
What is breast cancer?
Tumors are made when there is a buildup of unneeded, old and mutated cells that form a mass. Breast cancer is a malignant tumor, which is a group of cancerous cells that can grow and spread to surrounding tissues. Metastatic cancer occurs when the original cancer spreads away from the breast cells to other areas of the body.
Breast tumors can be either benign or malignant. Benign tumors are usually not harmful, while malignant tumors are serious and can spread to other parts of the body. When breast cancer cells spread, they usually first spread to the lymph nodes found in the underarms and above the collarbone.
The various stages of breast cancer depend on the size of the tumor and whether it has metastasized. A Stage I cancer is an early-stage breast cancer, while Stage IV indicates an advanced cancer that has spread to other parts of the body.
How common is breast cancer?
Breast cancer is the second most common cancer among women in the United States. About one in every eight women will develop breast cancer during their lifetime. Breast cancer occurs almost entirely in women, although men can get it, too. White women are at higher risk of getting breast cancer than black and Hispanic women,, although black women have the lowest survival rates.
There are many factors that can increase your likelihood for developing breast cancer. Non-modifiable risk factors include:
- Gender: Being female is the main factor that increases your risk of developing breast cancer.
- Age: The risk of developing breast cancer increases as you get older.
- Genetics: Some breast cancers are related to having unusual forms of certain genes, such as BRCA1 or BRCA2.
- Family history of breast cancer: If a relative has or had breast cancer, you are more likely to get it.
- Race and ethnicity: White women are more likely to develop breast cancer although black women are more likely to die from the disease.
- Women who began menstruation early (before age 12) are at higher risk for developing breast cancer.
- Having a vitamin D level < 50 ng/ml. 
There are also some lifestyle choices that can increase the likelihood of developing breast cancer. Besides vitamin D, modifiable risk factors include:,
- Pregnancy and breastfeeding: Women who do not have children or do not breastfeed their children are at a greater risk. Pregnancy and breastfeeding reduce the number of menstrual cycles in a woman’s life, which may decrease the risk of breast cancer.
- Long-term birth control: Women who use oral birth control pills during most of their child-bearing years have a slightly higher chance of developing breast cancer.
- Hormone therapy: Using combined hormone therapy with both estrogen and progesterone for more than two years increases the risk of developing breast cancer.
- Alcohol consumption: Chronic alcohol consumption may also increase the likelihood of breast cancer.
- Overweight or obesity: Those who are overweight or obese have a greater chance of developing breast cancer.
- Inadequate exercise: A sedentary lifestyle is associated with an increased risk of breast cancer.
- Cigarette smoke: Long-term smoking or exposure to secondhand smoke increases the risk of developing breast cancer.
What causes breast cancer?
While it is known that there are many factors that can increase an individual’s risk for developing breast cancer, researchers still don’t know exactly what causes breast cancer or what causes cells to become cancerous. Hormones play a key role in breast cancer, although it is not fully understood how or why.
Researchers know that cancers come from abnormal changes in cells and genes. For example, genes called tumor suppressor genes can slow the growth of cells into cancerous cells. When people have altered versions of these genes, they are unable to slow cancer cell growth, so breast cancer is more likely to develop. Some individuals may have changes to their oncogenes, the genes associated with cancer that are usually responsible for increased cell division and tumor production. When these genes are over-expressed, one’s risk for developing breast cancer increases.
We all have DNA mutations, which increase over over time, while others inherit them at birth. Researchers believe that exposure to radiation or certain chemicals may cause DNA changes that eventually result in cancer.
So, a combination of both genetic and environmental factors contributes to the development of breast cancer.
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 blood.
On paper at least, vitamin D is the perfect anticancer agent. As Holick (2006) reported, vitamin D helps prevent and repair the million per second cell mutations that are part of being alive. It also helps rid the body of mutated cells. It helps control abnormal cellular growth, helps prevent proliferation (when cells grow too fast), promotes apoptosis (the body’s way of getting rid of mutated cells), and plays several crucial roles in the functioning of the immune system.
Researchers have found a mechanism that may explain the relationship between vitamin D and breast cancer. Vitamin D receptors are 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, 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 (cancer genes) to die or stop growing and can stop 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.
What does the research say in general about vitamin D and breast cancer?
Treating breast cancer
Some studies have shown a link between vitamin D levels and breast cancer recurrence, 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 fact, a recent review concluded, “high vitamin D status is strongly associated with better breast cancer survival.”
In an even more recent review, researchers found that low vitamin D levels were associated with a twofold increased risk of cancer recurrence and mortality among women with breast cancer when compared to women with breast cancer and high vitamin D levels. The authors concluded, “… maintaining an optimal 25(OH)D status at diagnosis and during the 1-year follow-up period is important for improving breast cancer patient survival.”
Preventing breast cancer
A recent review of many studies found that post-menopausal women with low levels of vitamin D had a higher risk of developing breast cancer when compared to post-menopausal women with high levels of vitamin D.
Other studies have found a dose-response relationship, where for each set increase in vitamin D levels in the body; there is a concomitant decrease in breast cancer risk.
There are four types of studies that are used to determine whether sun exposure and vitamin D reduce the risk of breast cancer: geographical studies, observational studies, laboratory studies and randomized controlled trials. All four types of studies have found strong evidence that sun and vitamin D reduce the risk of breast cancer.
In geographical studies, the geographical variation in breast cancer incidence or mortality rates is compared statistically with solar UVB amounts. Such studies in Australia, China, France, Nordic countries, Spain and the United States have found lower breast cancer rates in regions of higher solar UVB.
Observational studies compare vitamin D levels with the incidence of breast cancer. There are two types of observational studies: those that look at vitamin D levels measured near the time of breast cancer diagnosis, called case-control studies, and those measured at the time women enroll in studies prior to diagnosis of breast cancer, called nested case-control studies. Only the case-control studies found that lower vitamin D levels are a risk factor for breast cancer.It is not known why the nested case-control studies did not have the same result.
Observational studies have also found that women with higher vitamin D levels at the time of breast cancer diagnosis live longer than those with lower vitamin D levels., In addition, black women with lower vitamin D levels are at a higher risk of dying from breast cancer after diagnosis than white women.
Finally, two randomized controlled trials found that vitamin D reduced the risk of various types of cancer, including breast cancer. In the first trial, postmenopausal women in Nebraska received 1,100 IU per day of vitamin D3 and 1,450 mg per day of calcium, resulting in a 77% reduction in all cancers between the first and fourth years of the trial, while those receiving only calcium had a 44% reduction. In the second study, the Women’s Health Initiative, women taking 400 IU per day of vitamin D3 and 1,500 mg per day of calcium experienced a decreased risk of both non-invasive and invasive breast cancers by 14-20%.
The role of sunlight in reducing the risk of breast cancer
There is growing evidence that sunlight reduces the risk of breast and other cancers. People who live in the sunnier regions of low to mid-latitude countries have lower breast cancer incidence and/or mortality rates than those living in the higher latitude, less sunny regions. For example, in the United States the lowest breast cancer mortality rates are in Arizona, New Mexico and Utah, while the highest rates are in the New England states. In addition, a recent study with mice found that the progression of intestinal cancers was reduced more by UVB exposure than by oral vitamin D intake, even when both treatments increased vitamin D levels about the same amount. Individuals concerned about developing breast cancer may reduce their risk by spending some time daily in the sun in a bathing suit, when their shadow is shorter than their height, which depends on the time of day and season.
Key points from the research
- Research from many studies shows that women with breast cancer are more likely to have lower vitamin D levels.
- Some research shows that post-menopausal women who do not get very much vitamin D may be more likely to develop breast cancer later in life.
- Research shows that women with breast cancer who have low levels of vitamin D are more likely to develop larger tumors and are more likely to have recurrent breast cancer.
- Studies show that women with higher vitamin D levels are less likely to develop breast cancer and less likely to die from breast cancer.
- Overall, more experiments are needed to give clearer answers regarding whether taking a vitamin D supplement can prevent or treat breast cancer. These studies are underway.
What does this mean for me?
Research shows a clear link between vitamin D and breast cancer. Numerous studies show that women with low levels of vitamin D are more likely to develop breast cancer.
Studies also show that in women who already have breast cancer, low levels of vitamin D are linked to more serious outcomes, including larger tumors, cancer spreading to other body areas, and death.
If you have breast cancer or are trying to prevent breast cancer and want to take vitamin D, it is highly unlikely to make your breast cancer worse or cause you any harm, as long as you take less than 20,000 IU per day and get your vitamin D level checked periodically. To help prevent breast cancer, women should achieve vitamin D blood levels of at least 60 ng/ml. This usually needs 5,000 to 10,000 IU/day of vitamin D. After you have been on vitamin D for several months, obtain a blood vitamin D level to see if you are above 60 ng/ml.
If you have breast cancer, we recommend you get your vitamin D blood level above 70 ng/ml. This will require anywhere from 5,000 to 15,000 IU/day. Make sure you get a vitamin D blood level after taking vitamin D for several months. Our low-cost in-home vitamin D blood test is an ideal way to monitor your vitamin D levels.
Also, remember that exposure to sunlight may help more than just taking vitamin D supplements. Our advice is to get both brief full-body sun exposure when your shadow is shorter than you are and take at least 5,000 to 15,000 IU/day on days when you can’t sunbath, such as during the winter. This may be especially important if you currently have or ever had breast cancer.
If you have breast cancer, you should not take vitamin D in place of your treatment medications. Modern science has produced many effective breast cancer medications. Vitamin D should only be used as adjunctive (add-on) treatment.
Keep in mind that you will never know if vitamin D helped. Breast cancer occurs in all age groups and can be either indolent (slow-growing) or aggressive, with or without vitamin D. You simply can never know what didn’t happen.
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