Estimating Vitamin D threshold for the Indian population: Delving into the actual disease burden

Based on the current guidelines in practice, a vast majority of the healthy Indian population is vitamin D deficient. Since the serum 25 hydroxycholecalciferol (25HCC) levels are affected by race and skin pigmentation, the normal range of vitamin D may differ in the Indians compared to the Western population. This study attempted to determine a population-specific threshold for 25 HCC levels associated with adequate bone health and calcium and phosphate homeostasis in healthy Indians.

Subjects aged 20-50 years were included in the study. The exclusion criteria were obesity, chronic renal disease, liver failure, diabetes mellitus, thyroid disorders, a recent history of fracture, constant joint pain, and postmenopausal status. In addition, participants on prescribed medication such as glucocorticoids, anticonvulsants, or antifungals, as well as vitamin D and calcium supplementation, were also excluded.Blood samples were analyzed for serum calcium, phosphate, alkaline phosphatase, 25HCC, 1,25dihydroxycholecalciferol, parathyroid hormone (PTH), procollagen type-I N propeptide, and C-terminal telopeptide of type 1 collagen.Locally estimated smoothing scatter plot (LOESS) curves and Spearman correlation were utilized to study the correlation of all the biochemical parameters with 25 HCC to achieve thresholds.

The study consisted of 270 healthy participants, out of which 97.8% were found to have vitamin D levels below 30 ng/ml. In addition, 8.8% had raised PTH, and 1.85% had hypocalcemia. Furthermore, 1.48% had raised serum alkaline phosphatase and hypophosphatemia, respectively. A weak inverse correlation was seen between 25 HCC and PTH (r_s = -0.437, p < 0.001), as well as alkaline phosphatase (r_s = -0.1475, p = 0.015), while a weak positive correlation was seen with serum phosphate (r_s = 0.128, p = 0.047).

For a healthy Indian population, the reference range of 25 HCC is much lower, and the lower limit of normal is approximately 13.5 ng/ml. This study indicates that vitamin D insufficiency in this population starts at 25 HCC values of 13.5 ng/ml and deficiency at 7 ng/ml.