In Reply: Dr Ding and colleagues highlight some challenges inherent in performing studies among individuals with knee osteoarthritis. As they indicate, in the interests of generalizability (and in the absence of compelling reasons for excluding any particular subset), our enrollment criteria were generally inclusive. Thus, we did have some participants with low levels of vitamin D (≤15 ng/mL). However, their numbers were small, and we do not place great weight on the apparently large but nonsignificant effect observed in this subset. Nevertheless, as we indicated in the article, we agree that there remains a possibility of benefit from vitamin D supplementation on knee osteoarthritis progression among individuals with vitamin D deficiency.
McAlindon T, LaValley M, Dawson-Hughes B. Vitamin D Supplementation in Patients With Osteoarthritis—Reply. JAMA. 2013;309(15):1583–1584. doi:10.1001/jama.2013.3778
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