To the Editor We read with interest the well-designed study by Miller et al.1Vitamin D deficiency (VDD) is an important health problem in elderly individuals, and the association of VDD and cognitive functions is an area that has drawn significant interest. There is also a great need to find factors related with the risk for dementia to have preventive measures for dementia, for which no curative treatment could be found to date. The findings of this prospective study with a long-term follow-up are valuable and indicate an association between VDD and dementia. However, we have some comments that could facilitate interpretation of the results.