What experts have to say
The connection between obesity and breast cancer is clear.
“For cancer prevention, the American Cancer Society recommends that people achieve and maintain a healthy weight throughout life… For those who are currently overweight or obese, losing even a small amount of weight has health benefits and is a good place to start,” Marji McCullough, ScD, strategic director of nutritional epidemiology at the American Cancer Society, told Healthline.
What’s still not clear is vitamin D’s role.
“This study measured vitamin D in the blood of women already diagnosed with breast cancer,” McCullough said.
“Their findings of lower concentrations in breast cancer patients compared to controls is consistent with some earlier studies. However, since vitamin D levels were measured after breast cancer was diagnosed, it is not known whether the low vitamin D levels influenced risk or were a result of breast cancer.”
Another factor is the often overlooked fact that there are many kinds of breast cancer. How one intervention affects risk for a certain subtype may not be consistent with others.
“Breast cancer is not one disease. We know that now,” Jean Sachs, chief executive officer of Living Beyond Breast Cancer, told Healthline.
“There’s not going to be one cure. There’s going to be many cures based on your particular subtype and genomic mutation.”
Like most things medical, it depends on who you ask.
“We always want to tell women… do no harm. It’s probably not harmful to take vitamin D, so why not do that?” Sachs said.
The American Cancer Society takes into account risk factors for vitamin D deficiency, such as age and geographic location, and recommended daily allowances when suggesting supplementation:
“The current RDA for vitamin D intake is 600 IU/day for most adults and 800 IU/day for individuals over age 70. For people who do not eat foods containing vitamin D, a supplement may be necessary. The National Academy of Medicine recommends not exceeding 4,000 IU vitamin D/day because very high levels can be toxic,” McCullough said.
“The benefits of vitamin D are still not proven, but it makes sense that women of all ages need adequate vitamin D levels for their bones, their immune system, and their health,” added Pinkerton.
“However, women also need to recognize that too much vitamin D can cause abnormally high levels of calcium in blood, which can lead to problems with blood pressure, bone loss, or kidney damage.”