A new preliminary study suggested vitamin D may be an important protection against a certain type of breast cancer and adult onset type 2 diabetes. But the vitamin is not without its dark side.
Researchers at Georgetown Lombardi Comprehensive Cancer Center, a part of Georgetown University Medical Center, found vitamin D significantly reduced development of estrogen receptor-positive (ER+) breast cancer in lean and obese mice, but had no effect in estrogen receptor-negative (ER-) cancer.
“In fact, obese mice destined to develop ER- breast cancer were clearly worse off than lean ER- mice given vitamin D in their diet,” said Leena Hilakivi-Clarke, Ph.D., a professor in the Department of Oncology and the study’s lead investigator.
Hilakivi-Clarke and colleagues also found no matter which breast cancer subtype the mice developed, vitamin D reversed insulin resistance in obese mice but increased insulin sensitivity in lean mice.
The use of vitamin D supplements is clearly tricky, Hilakivi-Clark said. “In many studies looking at the effect of vitamin D in different cancer types, there is no straight link between use and benefit.”
For example, vitamin D seems to reduce the risk of colon cancer development, but may not have any effect on later stage colon cancer. Experts are concerned vitamin D may actually increase the risk of prostate, esophageal and pancreatic cancers.
In her earlier studies on endometrial cancer, Hilakivi-Clarke found vitamin D wasn’t beneficial to lean mice, but in obese mice it reversed early and advanced stages of the cancer.
“This is not a vitamin to that should be taken lightly,” she said. “People need sufficient amounts of vitamin D for their overall health that have nothing to do with preventing cancer. But for those who want to boost their use of vitamin D, it’s important they have their individual levels tested by a physician and they discuss their desire to use supplement along with potential risks and benefits.”
Vitamin D is essential for improving muscle strength, immune function, absorbing calcium, maintaining healthy bones and the ability to reduce inflammation. Most people get vitamin D through sunlight exposure. It can be obtained through the diet by eating fatty fish, fish liver oil and eggs, some meat and cheese. Because very few foods contain natural vitamin D, most dietary vitamin D comes from fortified foods, such as milk, juices, yogurt, bread and breakfast cereals.
For the study, Hilakivi-Clarke fed lean mice two doses of 15 or 20 IU vitamin at the onset of puberty for 24 weeks. In lean mice given lower doses, they had fewer breast cancers and tumors took longer to develop compared to the control group. Obese mice were fed a higher dose of vitamin D (25 IU) because vitamin D tends to get trapped in fatty tissue and less gets into the bloodstream.
“The obese mice group destined to develop ER- breast cancer and fed vitamin D in their diet developed the highest number of cancers,” Hilakivi-Clarke said.
The researchers are currently studying possible mechanisms by which vitamin D may reverse obesity-induced increase in breast cancer and insulin resistance. Preliminary results suggested vitamin D reverses the action of genes that promote inflammation, cell proliferation and survival.
The National Cancer Institute has more information about Vitamin D and cancer: