Is There a Link Between Vitamin D and Breast Cancer?

There has been some disagreement over the connection between vitamin D levels and breast cancer. Current research shows that having low vitamin D levels might be linked to a higher risk for cancer recurrence. Vitamin D offers additional benefits for people trying to lower their risk of breast cancer as well as for people being treated for cancer.

This article gives an overview of vitamin D, the daily requirements, how it might affect your risk for different types of cancer, and its role in your overall wellness. The article will also provide information about breast cancer recurrence and prevention,

What Is Vitamin D?

Vitamin D is also known as calciferol or the “sunshine vitamin." It is a fat-soluble vitamin that helps with teeth and bone development. The human body produces vitamin D naturally through exposure to sunlight. When ultraviolet (UV) rays from the sun are on the skin, it triggers the body to make vitamin D. The vitamin is also present in certain foods and can be taken as a supplement.

Daily Requirements

According to the National Institute of Health (NIH), the daily vitamin D requirements—in both international units (IU) and the equivalent micrograms (mcg)—are:

• Birth to age one year: 400 IU/day or 10 mcg
• Between one and age 70 years: 600 IU/day or 15 mcg
• Over age 70 years: 800 IU/day or 20 mcg
• Pregnant and nursing people: 600 IU/day or 15 mcg

About 42% of people in the United States are vitamin D deficient. Risk factors for vitamin D deficiency include:

• Lack of sun exposure 
• Using sunscreen regularly (which is a good practice) 
• Having darker skin
• Not eating enough foods with vitamin D

Some people need to take supplemental vitamin D. These supplements come in two forms: D2 or D3.

D2 is naturally produced by some plants, while D3 is sourced from animals. Research has shown that vitamin D3 supplements increase vitamin D levels better than D2 supplements do.

Breast Cancer Recurrence

There is some disagreement among researchers about the connection between vitamin D levels and breast cancer. One reason is that there are many research variables, including different cutoff levels that studies use to measure vitamin D deficiency.  

Many studies have shown that a high percentage of people have low vitamin D levels when they are diagnosed with breast cancer. Current research has found that people with low D levels may have a higher risk for cancer recurrence and cancer spreading (metastasis). 

While there is a need for more randomized clinical trials to understand the connection better, here is what we do know about the possible link between vitamin D and breast cancer: 

• One study found that 45% of people with breast cancer had vitamin D levels below 20 nanograms per milliliter of blood (ng/ml) at diagnosis (compared to 34% in the control group)
• The average vitamin D levels in the breast cancer group were 26.88 compared to 31.41 in the control group. 
• Research has shown that vitamin D has anticarcinogenic properties which means it might help keep cancer cells from growing. 
• Animal studies have shown that vitamin D may play a role in controlling normal cell growth in breast tissue. 

There are still many unanswered questions about the connections researchers have found between different subtypes of breast cancer, obesity, and more advanced or aggressive cancers.

Regardless of the connection between vitamin D and cancer, healthcare providers will closely monitor your levels while treating you for breast cancer.

One reason for the need for monitoring is bone health, which is often a concern for people with breast cancer. Treatments such as chemotherapy or aromatase inhibitors decrease vitamin D levels, which lowers calcium absorption and increases the risk of osteoporosis. 

Breast Cancer Prevention

Research has suggested that vitamin D deficiency is a risk factor for breast cancer. However, there is no clear evidence of the therapeutic benefit of using vitamin D supplements to prevent breast cancer. 

Screening for vitamin D deficiency and the use of supplements has increased over the last 10 years. Healthcare providers and patients have noted the benefits of vitamin D supplements, including:

• Anti-inflammatory properties
• Anticarcinogenic (anti-cancer) properties
• Bone health
• Increased heart health
• Stronger muscles
• Immune function
• Low cost
• Few to no side effects or adverse effects

Vitamin D and Other Types of Cancers

There is ongoing research on vitamin D and cancer prevention. One area of interest is whether some types of cancer are more sensitive to vitamin D supplementation than others. Many studies show a relationship between low vitamin D levels and the incidence of other types of cancers, such as:

• Colorectal
• Kidney
• Lung
• Pancreatic 
• Prostate
• Blood cancers 

Overall Wellness

Vitamin D deficiency can have negative effects on your overall health. Your body needs vitamin D to support cardiovascular (heart), reproductive, immune, nervous, and skeletal muscle function.

Some specific roles of vitamin D in the body include:

• Bone growth and repair by helping the stomach absorb calcium and phosphorus
• Assisting with muscle movement
• Letting nerves carry signals to the brain
• Decreasing inflammation
• Building immunity
• Aiding in cell growth and division
• Helping with glucose metabolism

Vitamin D deficiency can contribute to health problems such as:

• Depression
• Sleep disorders
• Celiac disease
• Diabetes
• Osteoporosis and bone fractures
• Heart conditions
• Allergies
• Decreased muscle strength
• Neuromuscular diseases such as multiple sclerosis
• Increased infections
• Rickets (in children)

Effects of Too Much Vitamin D

Vitamin D is generally safe, and low levels are more common than high levels. However, too much vitamin D increases calcium which can cause kidney stones, heart problems, and bone weakness.

While toxicity is rare, it can occur with excessive doses of vitamin D. Signs and symptoms of vitamin D toxicity include:

• Vomiting
• Dehydration
• Pain
• Loss of appetite
• Muscle weakness
• Increased urination
• Kidney stones
• Kidney failure

Summary

The body naturally produces vitamin D through exposure to sunshine. It's also present in certain foods and can be taken as a supplement.

There is disagreement over the connection between vitamin D levels and breast cancer. However, research has shown that low levels of vitamin D are present at a higher rate in people with breast cancer. Vitamin D also offers additional benefits for people trying to lower their risk of breast cancer as well as for people undergoing cancer treatment. 

A Word From Verywell 

Vitamin D is generally considered safe, is low cost, and has many health benefits, but it’s always best to talk to your healthcare provider before you start taking a supplement. They can monitor your vitamin D levels and make sure you are taking the appropriate dose.