Vitamin D, cancer and Alzheimer’s
DEAR DOCTOR: I had my thyroid removed because of papillary cancer, and my surgeon has advised me to take high levels of vitamin D. He says there may be a correlation between low vitamin D levels and the development of cancer and Alzheimer’s disease.
DEAR READER: The normal blood level for vitamin D is between 20 and 50 ng/ml. This level — generally considered necessary for good bone health, but it’s about good bone health, not the prevention of cancer and Alzheimer’s disease. The World Health Organization looked at multiple retrospective studies evaluating a potential connection between vitamin D levels and colon cancer. They did find a link between low vitamin D levels and colon cancer, specifically that people with blood levels of 20 ng/ml or less had significantly higher colon cancer rates.
However, a study assessing vitamin D concentrations prior to the diagnosis of colon cancer did not find any evidence that vitamin D levels had any relation to colon cancer.
Studies focused on prostate cancer have
shown both benefit and increased risk among people with higher levels of vitamin D, so it would seem that supplementation does not appear to have an impact one way or another.
In summation, there may be slight benefit to minimal supplementation in women after menopause to get their levels to 35 ng/ml to decrease the incidence of breast cancer. But in men, the benefit of reduced cancer risk has not been shown.
In relation to cognitive decline, a study published in the journal Neurology in 2012 showed a slight increase in Alzheimer’s disease in people whose vitamin D levels were lower than 20 ng/ml. The authors concluded that more studies are needed to evaluate the potential connection. Ask your doctor if you can reduce the amount of vitamin D that you are taking, as there currently is no evidence to support it.
Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.