It is true that the DiaSorin assay for serum 25(OH)D (or D3!) measures the levels of both 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3. However, the radioimmunoassay measurements predominantly reflect the levels of D3, which contributes 93%–94% to the assessment of nutritional vitamin D status. It is, therefore, common practice to use the terms interchangeably. The 2003 edition of the American Society for Bone and Mineral Research Primer3,4 continues to refer to the analyte measured as 25(OH)D3.

I agree with Dr Harinarayan when he refers to the Lips’ classification. The reference ranges used by manufacturers do not truly reflect ‘normal’ values. This does not, however, take away from the conclusions of Tandon et al. As compared to published data on serum 25(OH)D levels in Indians, overall, Dr Tandon’s group clearly had far better data on the nutritional vitamin D status of Indians. The essential message that Indians can synthesize adequate amounts of vitamin D if exposed to enough sunlight is important and should not be lost in the debate over what constitutes normal.

It is true that no technique for estimating bone mineral density (BMD) is foolproof. However, at present, dual-energy X-ray absorptiometry (DEXA) continues to be the best and most widely used method. In fact, the WHO classification5 of osteoporosis incorporating T scores is based on the DEXA technique. Fluorosis can certainly interfere with BMD estimations, but this applies to all available techniques and is not specific for DEXA. It would be appropriate for studies from India to ideally measure the urinary fluoride levels also, at least in subjects who hail from areas known for fluorosis.
31 March 2004

Tandon N, Marwaha RK, Kalra S, Gupta N, Dudha A, Kochupillai N. Bone mineral parameters in healthy young Indian adults with optimal vitamin D availability. Natl Med J India 2003;16:298–302.

Mithal A. Bone mineral health of Indians. Natl Med J India 2003;16:294–7.

Golden L, Insogna, K, Wysolmerski JJ. Parathyroid hormone, parathyroid hormone related protein and vitamin D metabolites. In: Favus MJ (ed). Primer on the metabolic bone diseases and disorders of mineral metabolism. American Society for Bone and Mineral Research; 2003:155–66.

Kanis JA. Assessment of fracture risk. Who should be screened? In: Favus MJ (ed). Primer on the metabolic bone diseases and disorders of mineral metabolism. American Society for Bone and Mineral Research; 2003:316–22.

World Health Organization. Assessment of fracture risk and its application to the screening of postmenopausal osteoporosis. World Health Organ Tech Rep Ser 1994;843:1.