Regarding the article “Vitamin D and Risk of Cognitive Decline in Elderly Persons,” published in the Archives, July 12, 2010, the authors make a statement in the “Comment” section that
Furthermore, they state1(p1139)
This article may lead the reader to conclude that a low level of serum vitamin D in an elderly person would lead to a decline in cognitive function or dementia. Moreover, it may lead the reader to believe that supplementation with vitamin D would perhaps be beneficial and preventive. Usually, at baseline, one could discern major difference between elderly persons who have dementia with those who do not. For example, elderly individuals who have baseline dementia may have less physical activity, less sun exposure, or poor dietary habits. One can take any of these differences and perhaps show an association between these parameters and future development of dementia. To present data showing low levels of serum vitamin D and stating that “To our knowledge, no prospective study has examined the association between vitamin D and cognitive decline or dementia,” as shown in the abstract, is perhaps not appropriate.