Vitamin D May Help Prevent Breast Cancer, Among Other Benefits
We're all looking for ways to prevent cancer, and one may actually be in your medicine cabinet. That's right—vitamin D. Studies indicate a decreased risk of breast cancer for women with sufficient levels of vitamin D.
A 2011 study published in the American Journal of Clinical Nutrition reexamined data from the Women's Health Initiative's calcium and vitamin D clinical trial. The Women's Health Initiative (WHI) was a long-term, large-scale study of multiple health areas that ran from the early 1990s to 2005 and enrolled more than 161,000 women.
In the 2011 reexamination, women who were taking a combination of calcium and vitamin D provided by the clinical trial administrators had a significantly decreased risk—14 percent to 20 percent—of breast cancer. Women who were taking personal supplements in addition to the provided supplements did not see a reduction in risk. The study authors, therefore, concluded that the correct amount leads to a lowered risk of breast cancer, with no additional benefit provided by excess supplementation.
What else the WHI data tells us
Rebecca Jackson, M.D., led the landmark Calcium plus Vitamin D Supplementation trial that was published in 2006. She is the director of the Center for Women's Health, the founding director of the Center for Clinical and Translational Science, and a professor of endocrinology, diabetes and metabolism at Ohio State University in Columbus.
"The original question in the WHI study was: Does a calcium and vitamin D supplement help prevent bone fractures?" Jackson explained. "At that time, a handful of studies showed supplementation improved bone mineral density or at least slowed the loss. One French study of elderly people showed vitamin D decreased hip fractures."
During the seven years the WHI study followed postmenopausal women, it found several small benefits to a combination of calcium and vitamin D, including a slight decrease in the risk of colorectal cancer—but no prevention of bone fractures was found.
When the authors of the 2011 study dived into the data, they found the coadministration of calcium and vitamin D nonsignificantly reduced the risk of colorectal cancer by 17 percent but did not change the risk of fractures or total mortality.
Based on these findings, the National Academy of Medicine now recommends looking at vitamin D levels before adding supplementation, according to Jackson.
"While most people have sufficient levels, some health conditions cause absorption problems," Jackson said. "Typically, the amount in a daily multivitamin is enough. The body of literature doesn't support supplementation higher than the recommended dose, but it does support taking supplements if you're vitamin-D-deficient."
The health benefits of vitamin D
Maintaining adequate levels of vitamin D provides other health benefits, as well. Vitamin D helps the gut absorb calcium, which helps protect older adults from osteoporosis. It helps with bone growth, prevents rickets in children and prevents muscle cramps. Ongoing research shows other important roles. Vitamin D reduces inflammation and supports the immune system.
Most people in the world meet at least some of their vitamin D needs through exposure to sunlight.
"I don't advise people to get vitamin D from sun exposure alone," said Sagar Sardesai, M.B.B.S., a breast cancer oncologist with the Ohio State University Comprehensive Cancer Center. "There is an increased risk for skin cancer with too much sun exposure."
"Sun exposure allows our body to make [vitamin D], but there is no specific advice to spend a particular amount of time in the sun," added Erin Holley, R.D., a registered dietician at Ohio State University's Stefanie Spielman Comprehensive Breast Center.
Some studies suggest dietary intake of vitamin D may reduce breast density. Dense breasts are another risk factor for breast cancer, and a decrease in density could lower a woman's risk.
"Some researchers believe if you lower the density [with vitamin D], you lower cancer risk," Sardesai said. But more research is needed.
One of the limitations of vitamin D research is that many of the studies showing decreased risk of health problems thanks to vitamin D are observational studies, or comparative analyses that evaluate the results from multiple studies conducted on similar subjects or topics.
"Vitamin D studies are usually conducted with calcium. It's difficult in interventional trials to really know which one is responsible for outcomes," Sardesai explained.
Adequate vitamin D levels are important to overall health
As Jackson stated, current research does not support supplementing vitamin D at a higher than recommended dose, but it is recommended you supplement your intake if you are deficient in vitamin D.
Recent research is teaching us that adequate levels of vitamin D are tied to overall health, Holley added. For example, vitamin D is critical for cancer survivorship, she said. Many breast cancer survivors are placed on medication that stops the production of estrogen, which puts them at risk for bone density loss. Holley encourages the use of vitamin D and calcium supplements to prevent bone loss.
Supplements can be important if a patient has a health condition that causes deficiency. Holley recommended getting a blood test to determine the amount of deficiency before adding daily supplements. For most people who live in the sometimes sunlight-deprived North, some supplementation may be necessary to maintain adequate vitamin D levels, especially during the winter months, Holley said.
Salmon, sardines, tuna, white mushrooms and eggs are all rich sources of vitamin D. Other foods fortified with supplemental vitamin D include cereals and milk. However, Holley noted that making certain you're getting enough vitamin D can be difficult to guarantee with food alone.
The National Academy of Medicine recommends 600 international units (IU) per day for young adults and 800 IU per day for adults older than age 70. Adding up to 400 IU in a daily vitamin ensures adequate levels. While it's rare to get too much, excessive amounts of vitamin D can be toxic, which is why it's important not to take more than recommended.
"You just need to get enough," Sardesai said. "If you're meeting the recommended allowance, there is no evidence that more is better. It just needs to be sufficient. We don't know if it's going to prevent breast cancer, but we know it's healthier overall."