Vitamin D levels in newly detected Type 2 diabetes.

Sir,

The article by Laway et al. made for an interesting read.[1] Their observations on the association between 25-hydroxy Vitamin D [25(OH)D] levels and type 2 diabetes (T2D) around onset (newly detected, <6 months’ duration) are important addition to the existing literature on the connection between Vitamin D deficiency (VDD) and T2D. However, we feel that some alterations in the study design or analysis would possibly throw more light on this interesting link.

For a causal relationship, the temporality (exposure precedes disease) is of extreme importance in addition to other factors.[2] The obvious aim of the studies on patients with recently diagnosed T2D is to see if the measured Vitamin D concentrations can be linked to the initiation of the disease process. In this context, the timing of 25(OH)D estimation is crucial and has to be done as close to the onset of diabetes as possible. The ideal time therefore would be before the actual onset of disease, which is practically impossible to do unless an asymptomatic individual is undergoing periodic screening for T2D or participating in population screening studies as conducted in developed countries.[3] The next best time would be after the onset of diabetes, but before other factors (sun exposure, dietary Vitamin D intake, seasonal variation etc.) start influencing the Vitamin D status. These environmental factors may cause changes in Vitamin D status over days to weeks and hence VDD (considered to have a possible etiopathogenetic role) present before onset of diabetes may not be even detectable after 6 months of diagnosis.[4] It appears that 25(OH)D estimation to detect the state of permanent VDD should be done about a month after onset of diabetes, particularly in type 1 diabetes.[5] Since the timing of 25(OH)D estimation (average and range, in days) from the onset is not mentioned in the article it may be presumed that this was done closer to 6 months from diagnosis of diabetes. Consequently, it becomes difficult to exclude the effect of environmental influencers on estimated 25(OH)D levels. The sun exposure over long periods is particularly difficult to assess. In the light of above discussion, it may be worthwhile to do a reanalysis comparing 25(OH)D levels in patients where estimation was done closer to onset say around 1 month (time point 1) to those who had their levels estimated closer to 6 months from onset (time point 2) or simply correlate 25(OH)D levels in patients with the timing of measurement from onset or detection of diabetes. The findings of this subanalysis may bring to fore important facts on the link between Vitamin D and T2D in this patient population.