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Experts say vitamin D supplementation should be used only by certain groups that need it. Zeng Baoyan/EyeEm/Getty Images
  • Researchers say higher vitamin D levels may help improve a person’s odds of surviving breast cancer.
  • Experts say most people in the United States don’t have sufficient vitamin D levels because only a few foods contain the mineral naturally.
  • They add that vitamin D supplementation is necessary for only certain groups of people, including post-menopausal people.

Having enough vitamin D at the time of diagnosis is associated with better breast cancer outcomes.

That’s according to a new study highlighted at the American Society of Clinical Oncology 2021 virtual annual meeting.

Researchers measured vitamin D levels at the time of breast cancer diagnosis and then survival outcomes 10 years later in almost 4,000 people.

The researchers said they found vitamin D supplement intake, body mass index, and race/ethnicity were the most influential factors on vitamin D levels found in the blood.

Song Yao, PhD, the study’s lead author and a molecular cancer epidemiologist at the Roswell Park Comprehensive Cancer Center in Buffalo, New York, said in a press release that the findings provide the strongest evidence to date for maintaining sufficient vitamin D levels in breast cancer patients.

He said this is particularly true for Black women, who have a higher mortality rate from breast cancer than white women.

The researchers’ findings are consistent with earlier analysis on a smaller population, and experts say it’s significant to see the same trends in this much larger, longer-term data set.

Yao said this suggests an ongoing benefit for people who maintain sufficient levels through and beyond breast cancer treatment.

Marji McCullough, ScD, RD, a senior scientific director of epidemiology research for The American Cancer Society, told Healthline that most vitamin D research has focused on colorectal and breast cancers.

“Studies have shown that higher blood levels of vitamin D are associated with lower risk of colorectal cancer,” she said. “This study contributes to the evidence for a role of vitamin D in breast cancer survival.”

Higher blood levels of vitamin D means any level that meets or exceeds the “sufficient” clinical cut-off (≥30 ng/ml).

Vitamin D deficiency is less than 20 ng/ml, according to the National Institutes of Health’s Office of Dietary Supplements.

Does this mean vitamin D can fight breast cancer? Not exactly.

Dr. Nicole Williams, a medical oncologist specializing in managing the treatment of patients with breast cancer at The Ohio State University Comprehensive Cancer Center-Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, says the benefits of vitamin D for cancer prevention are mixed.

More research is needed before coming to any conclusions about the vitamin’s role in cancer outcome, she added.

“One of these studies was the VITAL (Vitamin D and Omega-3) Trial, which was the largest randomized clinical trial testing vitamin D for cancer prevention, and it was found that the supplement did not reduce the risk of developing cancer,” said Williams.

Vitamin D supplementation

Experts say most people in the United States consume less than the recommended amounts of vitamin D.

This may be because ways to get vitamin D naturally are limited. You can consume vitamin D from only a few foods or get it from sun exposure.

The National Institutes of Health lists these vitamin D-rich food options:

  • Cod liver oil
  • Trout
  • Salmon
  • Mushrooms
  • Fortified milks and juices
  • Fortified cereals

If you’re not sure you’re getting enough vitamin D, talk with your healthcare professionals.

“Generally, if you are healthy and aren’t getting treatment for any medical problems, you don’t have to worry about starting supplements,” said Williams.

But those in higher risk groups may want to get their levels tested.

Williams lists the following groups who may need supplementation:

  • post-menopausal women
  • men and women on long-term steroids
  • older adults (home-bound or in nursing homes/assisted living)
  • expectant and breastfeeding people
  • people with chronic kidney disease
  • people with parathyroid disease
  • people with obesity

So what does dark skin have to do with vitamin D?

“The higher melanin concentration in dark skin reduces the formation of vitamin D from sun exposure,” explains McCullough.

“It has been estimated that Black individuals need 5 to 10 times the amount of sun exposure to reach the same blood vitamin D levels as lighter-skinned individuals,” she says.

Williams added that there are likely multiple factors that explain the racial gap between vitamin D levels.

Multiple factors include adiposity, skin pigmentation, vitamin D binding protein polymorphisms, and genetics.

“No one factor alone can fully explain the vitamin D paradox in Black Americans,” said Williams.

The key takeaway

If you’re concerned about a family history of breast cancer or looking to stay as healthy as possible, talk with your doctor or dietitian about your vitamin D levels.

It’s important to do this before adding any new supplements to your wellness routine.

For example, McCullough highlights the need to review any supplements you take as these may already contain vitamin D.