In Reply Muratli et al raise the critical issue of whether there is a cause and effect relationship between low vitamin D status and accelerated rates of cognitive decline in older adults. We agree that dementia may lead to reduced vitamin D status owing to reduced exposure to sunlight, decreased dietary intake, and perhaps other circumstances, and therefore, reverse causation cannot be ruled out as an explanation for our results. Indeed, vitamin D status was lower on average in those participants in our study who were diagnosed as having dementia.1 However, as we stated in our report,1 we do not believe that the significant associations between low vitamin D status and rates of decline in episodic memory and executive function were due to higher prevalence of vitamin D deficiency in participants with dementia because the results remained similar after removing those participants from the statistical analysis. Importantly, participants diagnosed as having mild cognitive impairment and those considered to be cognitively normal had similar baseline vitamin D status.
Miller JW, Green R, DeCarli C. 25-Hydroxyvitamin D in Patients With Cognitive Decline—Reply. JAMA Neurol. 2016;73(3):358. doi:10.1001/jamaneurol.2015.4185