Defining role of vitamin D in cognitive decline.

Sir,

I went through the article entitled “Vitamin D as a marker of cognitive decline in elderly Indian population” published in ‘Annals of Indian Academy of Neurology’ (2015; 18:314-9) with interest.[1] Reports in the past have reflected on the widespread prevalence (50-90%) of vitamin D deficiency and its role as a risk factor for various health problems.[2] Keeping this in view, the study is an important addition to the published literature on health problems due to vitamin D deficiency. The authors deserve credit for this. However, I have a few points of concern with the study. The authors in their section on material and methods write that “The study population was divided into three groups; viz., patients suffering from AD and vascular dementia as well as patients with vascular cognitive impairment (VCI) not amounting to dementia (Group A, n = 32), patients with MCI (Group B, n = 24), and elderly age-matched controls (Group C, n = 30).” This statement seems a bit confusing as patients suffering from Alzheimer's disease (AD) and vascular dementia as well as patients with VCI not amounting to dementia have been grouped together as if they both mean the same. Also, in the analysis part, this group has been referred to as the “dementia” group only.

My second point of concern is about the matching of age among cases and controls. According to the authors, age-matched controls were chosen for cases but the ages of the three study groups varied. This is unlikely to happen if case matching is done on the bases of age, more so when the numbers chosen for each group are very small as matching age means having cases and controls of the same age.

This brings me to my other point of concern. In their table on cognitive assessment for the three groups (reproduced below), the authors have reported mild cognitive impairment (MCI) as mini-mental state examination (MMSE) score of 27.5 ± 1.3, which amounts to normal cognitive function and not impairment. The authors of MMSE recommended the following cutoff levels for classification purposes: Normal cognitive function = 27-30 and MCI = 21-26. Now, if a study participant scores normal in MMSE, how can he/she be included in the MCI group? The authors need to relook into this. Lastly, the authors need to have a look at the parameter column in the same table. The authors have written the MMSE score (range: 0-30; normal score <27), which seems inappropriate. As pointed out above, a score <27 means impaired cognitive function and is not normal.

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Conflicts of interest

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Table 1

Cognitive assessment of study groups