Vitamin D status has a profound effect on the growth and development of children and has major implications for adult bone health. Overt cases of vitamin D deficiency represent only the tip of an iceberg of vitamin D insufficiency. Whereas severe vitamin D deficiency, usually associated with 25-hydroxyvitamin D [25(OH)D] concentrations <5.0 ng/mL, results in rickets and osteomalacia, even less severe deficiency has been associated with numerous negative skeletal consequences, including secondary hyperparathyroidism, increased bone turnover, enhanced bone loss, and fracture risk.
In assessing a person's vitamin D status, because 1,25-dihydroxyvitamin D [1,25[(OH).sub.2]D] can be normal, high, or low in vitamin D deficiency, the most commonly used and most sensitive index is 25(OH)D. Age, sex, pubertal status, latitude, season, race, and ethnicity influence serum concentrations of 25(OH)D. The objectives of the current study were to assess the prevalence of clinical and biochemical vitamin D deficiency in healthy children and adolescents aged 10 y to 18 y during their period of most rapid growth, to compare the biochemical variables of the calcium-vitamin D axis between 2 socioeconomic groups, and to study the effect of hypovitaminosis D on BMD.
The study was conducted in 5137 apparently healthy schoolchildren (aged 10 y to 18 y) of both sexes in urban New Delhi, India. The children attended 2 state-run schools that catered to children of lower socioeconomic status (LSES) and 2 private schools that enroll children of upper socioeconomic status (USES). Socioeconomic stratification of the subjects was based on the type of school attended. Of the above 5137 subjects, 3089 (1079 boys, 2010 girls) from state-run schools made up the LSES group, and 2048 (968 boys, 1080 girls) from private schools made up the USES group. The subjects were further divided into 3 age groups: 10 y old to 12 y old, 13 y old to 15 y old, and 16 y old to 18 y old.
This entire cohort of 5137 children and adolescents underwent clinical examination and anthropometric assessment, including a recording of the stigmata of vitamin D deficiency. A sunlight exposure questionnaire was administered to each child. Clinical vitamin D deficiency was diagnosed if a subject had either genu varum (bowlegs) or genu valgum (knock-knees). Of this large cohort, 760 children (430 from LSES and 330 from USES groups) selected by randomization from each class of the school underwent further laboratory assessment. Each class was divided into four groups according to the number of sections in the class, and all children from one randomly selected section (cluster) were called for blood sampling the next day. Dietary assessment of total energy, protein, carbohydrate, fat, calcium, and phytate was done in 349 subjects randomly selected from the cohort of 760 (171 from the LSES and 178 from the USES groups) through a 24-hour recall of their food intake.
A total of 5137 children were examined, and a 10.8% prevalence of clinical evidence of vitamin D deficiency was noted in 556 children. Boys had a prevalence of 10.4% and girls had a prevalence of 11.1%, and there was no significant difference between the 2 groups. This study found that the LSES group adolescents had significantly lower mean 25(OH)D concentrations than did the USES group adolescents. The only other study that compared low and high socioeconomic status groups did not find any significant difference in mean vitamin D concentration between the two groups. However, the difference that these researchers found is further supported by the observation that LSES group children also had higher iPTH, higher AP, and lower serum phosphorus concentrations than did USES group children. Because serum calcium concentration and sunlight exposure did not differ significantly between the two groups and because dietary calcium intake was significantly lower in the LSES group than in the USES group, nutrition may play an important role, as was reported earlier.
Children in the LSES group had significantly lower BMD values at the forearm than did those in the USES group. This difference could be due to poor overall nutrition, as evidenced by low BMIs, low dietary calcium intakes, low serum 25(OH)D concentrations, and secondary hyperparathyroidism. The researchers conclude that there is a high prevalence of clinical and biochemical hypovitaminosis D in apparently healthy schoolchildren in India. The observation that children from low socioeconomic backgrounds have significantly higher prevalences of vitamin D deficiency and low BMD suggests that nutrition plays an important role in the causation of hypovitaminosis D.
R. Marwaha, N. Tandon, D. Reddy, H. Reddy, et al. Vitamin D and bone mineral density status of healthy schoolchildren in northern India. AJCN; 82(2):477-482 (August 2005) [Correspondence: RK Marwaha, Department of Endocrinology and Thyroid Research, Institute of Nuclear Medicine and Allied Sciences, Timarpur, New Delhi 110054, India. E-mail: email@example.com]
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