Should You Take Vitamin D While Receiving Chemotherapy? What to Know About Vitamin D and Cancer

Cancer has many causes — from inherited genes and tobacco smoke to sun exposure and pollution. And sometimes cancer appears even without a known cause. So it’s no wonder that there’s a lot of interest in whether certain vitamins and supplements can help prevent or treat cancer. And one that often comes up is vitamin D.

Vitamin D helps your body absorb calcium to support healthy bones. It also plays a role in inflammation, your immune system, and cell growth. But is there a connection between vitamin D and cancer? And should you take vitamin D if you’re receiving chemotherapy?

What’s the connection between vitamin D levels and cancer?

Researchers are still studying the relationship between vitamin D and cancer. We’ll summarize some of what scientists have learned so far.

More sun exposure is associated with a lower risk of some cancers

A review of studies across several countries found that areas with more sun exposure had a lower incidence of certain types of cancer, including:

• Bladder cancer

• Breast cancer

• Cervical and vulvar cancer

• Colon and rectal cancer

• Endometrial cancer

• Stomach cancer

• Lung cancer

• Ovarian cancer

• Pancreatic cancer

• Renal (kidney) cancer

• Hodgkin’s and non-Hodgkin's lymphoma

Your body makes vitamin D when it's exposed to sunlight. This led scientists to consider that the lower cancer levels in areas with more sunshine could be due to higher levels of vitamin D.

Low vitamin D levels are associated with an increased risk of certain cancers

Low vitamin D levels are associated with an increased risk of certain cancers in some studies. But often, the results are mixed and can vary depending on the type of cancer.

Most studies show a higher risk of breast cancer in people with low vitamin D levels. And higher vitamin D levels are associated with a better breast cancer survival rate, lower risk of triple negative breast cancer, and lower risk of relapse. But other studies, including a review of over 20,000 people, show no association between vitamin D levels and the risk of developing breast cancer. So the connection between vitamin D levels and breast cancer is unclear.

Most studies show an association between low vitamin D levels and a higher risk of colon cancer. And as with breast cancer, higher vitamin D levels are associated with a higher survival rate in people with a colon or rectal cancer diagnosis.

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Several studies have also found a link between low vitamin D levels and a higher risk of prostate cancer. And higher vitamin D levels seem to lower the risk of prostate cancer worsening or spreading. But other studies found that higher vitamin D levels were associated with an increased risk of developing nonaggressive prostate cancer. So it’s unclear what role vitamin D plays in prostate cancer at this time.

Most studies show a link between low vitamin D levels and certain lymphomas. Not only is low vitamin D associated with a lower survival rate, but it may also make treatment less effective for these cancers.

There’s some evidence that low vitamin D levels may also raise the risk of some cancers of the mouth, bladder, and lungs. But more studies are needed to know for sure.

Does taking vitamin D help prevent or treat cancer?

If low vitamin D levels are associated with an increased risk of some cancers, then it’s logical to think that taking vitamin D would reduce your risk of cancer. But the evidence doesn’t seem to show that taking vitamin D helps prevent cancer in most cases.

A 5-year study, called the VITAL study, found that there doesn’t seem to be a relationship between taking vitamin D and the overall risk of getting cancer. But for people without excess body weight who develop cancer, it may slightly lower the risk of advanced cancer.

A 2019 review of clinical studies also found that taking vitamin D may lower your risk of death from cancer, even though it didn’t change your risk of getting cancer. A more recent review found that vitamin D supplements had no effect on the risk of getting cancer or the risk of death from cancer.

That being said, there may be a difference in how taking vitamin D affects certain types of cancer. For example, one study found that taking vitamin D reduced the risk of relapse or death for some cancers of the digestive tract. But it was only effective for cancers that tested positive for a specific protein.

At this time, the evidence doesn’t support taking vitamin D to prevent or treat cancer. But the potential benefit of vitamin D remains of great interest to scientists and healthcare professionals. There are a number of ongoing clinical studies looking at the effect of vitamin D supplements on certain cancers. So it’s possible there’s potential we haven’t yet discovered.

Should you take vitamin D if you have cancer or while receiving chemotherapy?

You should only take a vitamin D supplement if your healthcare team recommends it.

Your oncologist may also recommend a vitamin D supplement to help prevent bone loss caused by certain cancer treatments. And vitamin D in an oral gel form may help prevent mouth and gum sores (mucositis), a common side effect of chemotherapy and radiation.

Keep in mind that vitamin D isn’t safe for everyone. Vitamin D can raise your calcium levels, which can cause nausea, muscle weakness, and kidney stones. Some cancers can also cause high calcium levels, so taking vitamin D may worsen this side effect. Too much vitamin D can cause kidney problems, heart problems, and even death. So be sure to check with your oncologist before taking it to make sure it’s safe for you.

How do you know if your vitamin D levels are low?

Low vitamin D levels are common in people living with cancer. If this is a concern for you, ask your oncologist for a blood test to check your vitamin D level. They’ll be able to recommend the right vitamin D dosage for you if it’s needed.

Other factors can increase your risk of low vitamin D levels, such as:

• Limited sunlight exposure

• Older age

• Darker skin tone

• Larger body size

• Inflammatory bowel disease

• History of gastric bypass surgery 

• Medications, such as antiseizure medications and some blood pressure medications

• Chronic kidney or liver disease

Keep in mind that spending 10 minutes a day in the sunshine is typically enough to make the vitamin D you need. And regular exercise is recommended not only to help prevent cancer, but to improve stress levels and combat fatigue during treatment. So taking a short walk outside can help you get the best of both worlds.

What other supplements are recommended if you’re being treated for cancer?

When it comes to taking vitamins and supplements, there’s not a one-size-fits-all recommendation for cancer. It depends on the type of cancer you have, your treatment plan, and other factors.

Keep in mind that even though supplements are often made from “natural” products, that doesn’t mean they’re risk free. Some vitamins and supplements can make cancer treatments less effective. Others can raise your risk of bleeding or other side effects.

The best way to ensure you’re getting the vitamins you need is to focus on what you’re eating. You can also talk to your oncologist about complementary and integrative treatment options. These customized services can help you find safe options that support your cancer treatment, such as acupuncture and meditation. They can also provide nutrition counseling and let you know if any vitamins or supplements are a safe option.

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Written by:

Patricia Weiser, PharmD

Patricia has 16 years of pharmacist experience. She previously held positions as a community pharmacist, pharmacy manager, and hospital pharmacist.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Karen Hovav, MD, FAAP

Karen Hovav, MD, FAAP, has more than 15 years of experience as an attending pediatrician in a variety of clinical settings. She has worked in a large academic center in an urban city, a small community hospital, a private practice, and an urgent care clinic.

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