Updated: Sep 26, 2019
Vitamin D levels may be related to cancer but are supplements safe?
Vitamin D is a fat soluble vitamin that is produced in the body in response to sunlight, obtained through food, or by taking supplements. Studies of Vitamin D levels and breast cancer outcomes are mixed. However, researchers at Stanford University School of Medicine have found an association between Vitamin D levels and an the expression of an oncogene called ID1. This oncogene is associated with tumor growth and metastases. When Vitamin D is converted to calcitriol, calcitriol binds to the Vitamin D Receptor (VDR), which regulates many cancer genes. Dr. Feldman and the team at Stanford injected breast cancer and found that the mice who were placed on a low Vitamin D diet developed tumors faster and the tumors were larger. They also found that the aggressive line of breast cancer cells had low VDR expression compared to those lines that did not metastasize. They concluded that a loss of Vitamin D/VDR signaling was sufficient enough to give cells the ability to metastasize. They also suggest that the Vitamin D receptor regulates the ID1 oncogene. In a small clinical trial, women with early stage breast cancer who had higher levels circulating Vitamin D had lower ID1 expression in their tumors. Unfortunately, this trial was stopped before patient outcomes could be assessed. Please see the blog from the website of the National Cancer Institute.
There are two reasons that breast cancer survivors should be evaluated for Vitamin D deficiency and treated as necessary. We know that breast cancer patients are at increased risk of fractures regardless of age. Please see the article in BMC Cancer. In addition, Vitamin D may play a role in cancer recurrence.
Update 8/22/19: A recent meta-analysis of cardiovascular risks (CV) and benefits with vitamin intake published in the Annals of Internal Medicine found Calcium and Vitamin D supplementation to be associated with a 17% increase risk of CV disease with moderate certainty. Other significant outcomes were a 33% decreased mortality with reduced salt intake in hypertensive patients and 10% decreased mortality in normotensive patients. Studies are still controversial and have been for years. Omega 3 fatty acid supplementation was associated with an 8% decrease in myocardial infarction (evidence of low certainty). Folic acid supplementation conferred a 20% decrease in stroke (low certainty).
My take on this is that if your Vitamin D levels are within the normal range, it may be wise to skip supplementation as Vitamin D increases the absorption of calcium, which is attracted to sites of inflammation including blood vessels.
Update 9/26/19: A double-blinded randomized clinical trial in Canada published in JAMA Aug 27; 322:736 investigated bone-mineral density (BMD) in 311 adults without osteoporosis and who had normal baseline Vitamin D (Serum 25-hydroxyvitamin D) levels. They were randomly assigned to receive either 400, 4,000, or 10,000 IU of Vitamin D3 daily. Participants were assessed serially over a 36 month period using high-resolution computed tomography of the distal radius and tibia. Serum 25-hydroxyvitamin D levels only increased in the 4,000 and 10,000 IU groups. The results were rather unexpected! BMD actually declined significantly faster in the 4,000 and 10,000 IU groups! Bone strength also declined in all three groups with nonsignificant trends towards less strength in the higher dose groups. The authors postulate that the high intake of #VitaminD3 may suppress the parathyroid hormone resulting in increased bone resorption. It appears from this study that higher doses of Vitamin D3 supplementation does not benefit bone integrity. However, I would still like to see a larger study and more detailed information regarding exercise routines as weight-bearing activities are important for bone health.
*Do not take this or any other medication during chemotherapy, radiation therapy, or after therapy without first consulting your doctor.