The NMJI

We would like to thank Dr Harinarayan for his constructive comments. We agree with him that the vitamin D kit used by us (DiaSorin) indeed measures both 25-hydroxyvitamin D3 and -D2. 25-hydroxyvitamin D3 is the predominant form of 25-hydroxyvitamin D in the blood. Hence, conventionally and by precedence, the term used has been 25-hydroxyvitamin D3. Dr Harinarayan has also used the term 25-(OH)D3 while referring to the analyte measured by a similar kit based on radioimmunoassay.1

Once again, we agree with the comment that two concepts, namely ‘population-based reference range’ and ‘functional health-based reference value’ are used when discussing vitamin D deficiency. While there is no doubt that the population-based reference range will be influenced by several extraneous factors and so cannot necessarily be extrapolated to different regions of the world, this range has been used in earlier publications when discussing hypovitaminosis D. There also appear to be differences in opinion as to what constitutes ‘functional vitamin D deficiency’. In the review by Lips,2 different studies refer to different possible cut-offs in the range 10–30 ng/ml for defining a functionally low vitamin D level. Also, most of the analyses to arrive at a reference value of vitamin D deficiency comes from studies conducted in the elderly who do not have the same responses to the vitamin D–parathyroid hormone (PTH) axis as healthy young adults. Since this issue is far from resolved, the population-based reference range is equally acceptable for defining vitamin D deficiency as is the case for several other analytes. With specific reference to the 9 subjects with elevated alkaline phosphatase, the break-up of their vitamin D levels shows (as per Lips classification): 4 to have mild vitamin D deficiency and 5 to have normal vitamin D levels; none had levels below the normal range of the kit. This does not support the speculation of Harinarayan. Hence, we also do not agree with his last statement that the paper brings out mild vitamin D deficiency in some healthy young Indian adults. Further, Harinarayan makes an erroneous observation, namely, that there were cases with elevated PTH levels. We clearly state that there was no subject with an elevated PTH level (p. 299, right column, para 2, line 1).3

With regard to bone mineral density (BMD), we agree with Harinarayan’s statement about the possible limitation of dual-energy X-ray obsorptiometry (DEXA) in a country with endemic fluorosis. We have also raised the issue in our article for the need to establish ethnically appropriate BMD norms. We, however, do not agree with his speculation of the possibility haematological disorders, since the study was conducted in a group of healthy paramilitary personnel who undergo regular (at least annual), thorough, physical examination.
20 March 2004