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Ask a Scientist -- Dr. Carlos A. Camargo, Jr.

Questions and Answers with Dr. Carlos A. Camargo, Jr., MD, Dr. PH
Harvard Medical School

Response to newsletter, September 2, 2015 Does Vitamin D prevent colds and flus? Our D*action data says that it does, along with some research papers. 

Vitamin D below 20 ng/ml (50 nmol/L)

Q: In my pediatric practice it appears that children get sick much more frequently when vitamin D drops below level of 50. Has anyone studied this? This seems to happen especially after the holidays when families are busy and forget doses. – Michael W. Shannon, M.D. Pediatrician

A: Hello Dr Shannon, I assume that you mean a 25(OH)D level <20 ng/ml (<50 nmol/L)? If yes, there are many studies that show that people with 25(OH)D levels <20 ng/ml are at higher risk of infections than those with higher 25(OH)D levels. If you actually meant <50 ng/ml (<125 nmol/L ), I’m not aware of data that supports your clinical observation of possibly different infection risk for someone with level of, say, 45 vs 55 ng/ml. Many studies do suggest a dose-response relationship up to a threshold around 30 ng/ml (75 nmol/L). Looking ahead, we are nearing completion of an individual patient data meta-analysis (IPDMA) that brings together data from around 20 randomized controlled trials on vitamin D supplementation and risk of acute respiratory infection; we should be able to better identify the 25(OH)D threshold for infection benefit in early 2016.

Supplementation vs. the flu shot

Q: How do you think Vitamin D supplementation compares to the flu shot to prevent the flu?

A: I’m not aware of any head-to-head comparisons but will point out that we do not have to choose only one of these interventions. As a physician, who gets lots of exposure to the flu, I will get my annual flu shot soon and also will continue to take my daily vitamin D supplement!