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A new study on the association between vitamin D and the reduced risk of breast cancer suggests that higher concentrations of the micronutrients may be a factor.

Research on the role of vitamin D and its influence on breast cancer isn’t new. Data has shown that women with low levels of the vitamin are at higher risk for developing the cancer.

But there isn’t enough evidence yet to directly link high levels of vitamin D to a decreased risk for breast cancer.

This new study, conducted by researchers at the University of California San Diego in collaboration with Creighton University, Medical University of South Carolina, and Grassroots Health, may shed some new light on relationship between the two.

Dr. Scott Christensen, professor of hematology and oncology at University of California Davis and medical director at the U.C. Davis Cancer Care Network, told Healthline he was cautiously optimistic about the study.

He likened it to an “informational advancement” on the role of vitamin D in relation to the development of breast cancer.

“We’ve gone from [thinking] vitamin D may help to maybe now there are different levels that can help,” he said. “It certainly raises some very provocative questions about the role of vitamin D.”

What the research revealed

The findings are based on a meta-analysis of previously conducted clinical trials.

One of the studies involved more than 3,300 participants and the other had more than 1,700 participants. The studies were conducted between 2002 and 2017.

All participants were women over the age of 55 and cancer-free at the time of enrollment. During the trials they were given both vitamin D and calcium supplements and were followed for a mean period of four years.

The crux of the study is the concentration of vitamin D found within blood. Researchers referred to it as serum 25-hydroxyvitamin D, or 25(OH)D, which is the main marker of vitamin D in blood.

The authors concluded that women with a higher concentration of vitamin D in their blood had a lower risk for breast cancer compared with women who didn’t have these higher levels.

“Participants with blood levels of 25 (OH)D that were above 60 ng/ml had one-fifth the risk… compared to those with less than 20 ng/ml,” Cedric Garland, principal investigator and co-author, said in a press release.

What vitamin D does

Vitamin D is vital to your overall health.

It helps muscles move, lets nerves carry signals, and helps your immune system ward off disease.

“We know vitamin D keeps bones strong and it has an important role in normal cell growth,” Dr. Marissa Weiss, chief medical officer and founder of Breastcancer.org, told Healthline.

Weiss also practices at Lankenau Medical Center in Pennsylvania and serves as the director of breast radiation oncology and breast health outreach.

The current recommended daily allowance of vitamin D for people ages 1 to 70 is 600 International Units (IU). This includes pregnant women. From birth to 12 months, it’s 400 IU. Adults over the age of 70 should have 800 IU.

There are two main ways for people to get enough vitamin D — through food and from the sun.

Oily fish such as salmon, sardines, and oysters are good sources of vitamin D. Supplements are another way to boost your intake.

Vitamin D is also produced in the body and stored in its inactive form, predominately in the skin. When people expose their skin to the sun, the rays transform the vitamin to its active form.

A lack of vitamin D

Both Weiss and Christensen say that concern over skin cancer due to sun exposure has resulted in a vitamin D deficiency in many populations.

Studies have shown an association between the decline in vitamin D consumption and the rise in breast cancer rates, but no study has made the direct link, according to Weiss.

“Breast cancer is on the rise so is one reason [a lack of] vitamin D?” she said. “It’s possible.”

The tricky thing about vitamin D deficiency is that there aren’t any symptoms, Weiss added. The deficiency is invisible so the only way to find out is through a blood test that checks vitamin D levels.

She noted that women in particular should get their levels detected so they can figure out if they need to take in more vitamin D either through food or a supplement.

“People need to know and they should talk their doctor about it,” Weiss said.

Only part of the equation

Christensen cautioned though that vitamin D isn’t the only factor that can influence the development of breast cancer.

Like all cancers, breast cancer is caused by a multitude of issues. Diet, exercise, lifestyle choice, and genetics all play a role. Vitamin D is just one part of that equation.

But, the study out of U.C. San Diego certainly advances the line of inquiry regarding vitamin D and breast cancer, he added.

The next steps would be more in-depth trials, such as ones that take age or high-risk populations into consideration when assessing vitamin D and association with breast cancer.

“It’s worthy of further investigation, though,” Christensen said, “because there’s a signal there.”