Vitamin D levels in relation to other calcium and phosphate regulating hormones in children in Murmansk and Groningen. Effect of summer and winter. A pilot study.

Rationale: Vitamin D (Vit D) is a vitamin that is well known for its action on
bone maturation and calcification. Vit D improves the uptake of calcium in the
gastro-enteral tract and the deposition in bone. A lack of vit D, but most
likely a lack of both vit D and calcium, can cause nutritional rickets. Studies
done over the past years have shown more effects of vit D in the human. Low
levels of vit D are in children related with a higher risk on Diabetes Mellitus
type 1, multiple sclerosis, Crohn*s disease and Rheumatoid arthritis, all
autoimmune diseases. Recently, an effect of vit D is also shown on other
autoimmune diseases, astma and atopic dermatitis. An unsolved question is how
to define vit D deficiency or the optimal level of 25 hydroxyvitamin D
(25OHD). The European Society Pediatric Gastroenterology and Nutrition and the
European Society Pediatric Endocrinology defines a level of > 50 nnmol/l as
sufficient. Vit D is produced in the skin and absorbed from certain foods. It
is presently unknown how much vit D is produced in the skin of infants, if this
amount is sufficient to reach a level of 25OHD above 50 nmol/L. The production
of vit D in the skin is higher in summer compared to winter. Studies in 6-8
year old children found that up to 50% of these children in the Netherlands
have 25OHD levels < 50 nmol/l in wintertime. The difference in vit D production
between summer and winter might be very important in Murmansk, a city in the
far North of Russia. No study so far evaluated if the recommended dose of vit
D, 400-600 IU is sufficient for infants in winter in Murmansk or also needed in
summer time. The role of calcium intake, levels of plasma PTH, 25OHD and
fibroblast-growth factor 23 (FGF23), an important phosphate regulating hormone,
will be evaluated in relation to the severity of rickets, defined by the
increase of alkaline phosphatase.

Objective: To obtain data to be used for designing a larger scale study on the
incidence of 25OHD levels below the recommended level of 50 nmol/l in children
in Murmansk, Russia and Groningen, the Netherlands.

Study design: Observational study with invasive methods ( blood taking). Serum
calcium, phosphate, alkaline phosphatase, and plasma 25OHD, PTH and FGF23
will be measured in children 1-4, 5-8 and 9-12 years in both Groningen and
Murmansk. Blood will be taken in July/August and January/February

De risico's en belasting van het onderzoek zijn minimaal. Op basis van gegevens
uit deze studie kan een veel gerichtere studio opgezet worden naar de eventuele
noodzaak van suppletie van vit D bij kinderen op verschillende leeftijden, in
de winter en/of de zomer en in Murmansk en Groningen. Dit is van groot belang
voor grote groepen kinderen.