Bone health is affected by chronic childhood disorders including type-1 diabetes mellitus (T1DM).1 The International Society for Pediatric and Adolescent Diabetes (ISPAD) clinical practice consensus guidelines (2018) report osteoporosis and increased risk of fractures as key complications of T1DM.2 The guidelines also suggest that in patients with T1DM, adequate nutrition including calcium intake, maintenance of adequate vitamin D concentrations, avoidance of smoking, and regular weight-bearing exercise are important for bone health.2 In 2021, the International Diabetes Foundation identified 229.4 thousand cases of T1DM among children and youth aged 0–19 years in India.3 T1DM cases, particularly among younger cohorts, increases the risk of both osteoporosis and fractures among those with poor glycemic control, dyslipidemia and other microvascular complications.4 High prevalence of vitamin D deficiency is a primary contributing factor to poor bone health in these children, thus guidelines recommend sufficient calcium intake and vitamin D supplementation as interventions to improve bone health. Vitamin D supplementation along with calcium has also been shown to improve bone mineral density (BMD) in children with T1DM.5 Hence, it is suggested that children and adolescents with T1DM need to have adequate calcium intake (1200 mg/day) and supplementation with vitamin D if they are vitamin D deficient.5

A meta-analysis of 9 studies reported lower BMD in participants with T1DM in 5 studies while 4 have shown no significant differences.6 Another meta-analysis on Dual Energy X-ray Absorptiometry (DXA) and peripheral Quantitative Computer Tomography (pQCT) based studies found that the mean tibial trabecular volumetric BMD and radial trabecular volumetric BMD were significantly lower in youth with T1DM.7 The factors resulting in low BMD in T1DM are insulin deficiency which causes loss of bone anabolic action, poor glycaemic control leading to increased renal calcium excretion, and associated deficiency of other bone anabolic peptides like amylin and other associated autoimmune disorders.8 In previous cross-sectional DXA-based studies, our team has shown that Indian children and adolescents with T1DM had short and narrow bones with an increasing duration of diabetes.9 In another case-control study on 251 Indian children with T1DM, we found that pQCT-derived trabecular and total volumetric density at the 4 % radius (proximal radius) was lower in patients with T1DM and the former was negatively correlated with HbA1C concentrations.10

As calcium and vitamin D are widely considered critical for osteoporosis prevention and treatment, supplementation with these is recommended.11 Pharmacological calcium supplementation and calcium intake via food, particularly dairy products, are commonly encouraged modalities of supplementation.12 Very few randomized controlled trials have compared outcomes of equivalent amounts of absorbable calcium from dairy food vs. pharmacological supplements on bone outcomes.13 To the best of our knowledge, there has been no study comparing the effect of supplementation with calcium on bone health in children and adolescents with T1DM via milk vs. pharmacological calcium supplements.

A study on 173 children and adolescents aged 7–18 years has demonstrated higher concentrations of bone resorption markers to be associated with lower concentrations of HbA1c, thus suggesting an interaction between bone and glucose metabolism.14 Increased HbA1c concentrations have been reported to be associated with low bone mineral density.7 We conducted this study with the primary objective of investigating the effect of 1-year supplementation with vitamin D with milk or with calcium (pharmacological as tablets) on bone mineral density and cortical thickness of underprivileged Indian children and youth with poor glycaemic control of T1DM. Our secondary objective was to study of effect of supplementation on lipid profile, glycaemic control and serum calcium concentrations. We hypothesized that the group of participants with T1DM receiving vitamin D with milk, due to the anabolic effect of protein, would have better cortical thickness at 66 % radial site (distal radius where cortical bone density is measured by the pQCT) than participants receiving vitamin D with pharmacological calcium or controls (with diabetes).