A study in the Lancet Diabetes & Endocrinology looks at the relationship between vitamin D supplementation and rates of bone fractures in Mongolian schoolchildren.

The authors conducted subgroup analyses in a subgroup with baseline low vitamin D status (below 25 and 50 nmol/L) and low calcium intake (below 500 milligrams per day), and found similar results compared to the overall cohort. However, there are several major limitations to the results of this study.

Improving vitamin D status in Vitamin D deficient populations improves calcium absorption from the diet and incorporation of calcium into the skeleton.  However, when calcium intakes are well below the recommended intakes, or even below the average requirements, the amount of calcium absorbed from the diet may still be below the amounts needed for appropriate accrual of bone mass during growth.

Based on the data reported, my estimation is that the calcium intakes were below the nutritional recommendations and even average requirements in the majority of children.  The authors have applied a threshold for their subgroup analysis of a calcium intake below 500 milligrams per day; this is well below the recommended intakes or estimated average requirements for children of the age group investigated in this study (see for example population guidelines for children formulated by the WHO (world), EFSA (Europe), NAM (US and Canada) and SACN (UK)).

The work was robustly conducted, in a well characterised study population, using validated methods – particularly with respect to the standardisation of vitamin D status measurements, and included children recruited from multiple sites across a large number of schools and thus representative of the younger population in Mongolia.