Vitamin D deficiency in healthy children in a sunny country: associated factors

Objective The objective of the present study was to determine the factors associated with low concentrations of 25-hydroxy vitamin D (vitamin D deficiency) in healthy children in Qatar. Design The survey was a cross-sectional study conducted at the Primary Health Care Clinics over the period from August 2007 to March 2008. Subjects The study was carried out among healthy Qatari nationals, male and female, aged below 16 years. A random sample of 650 healthy subjects who visited the Primary Health Care Centers for any reason other than acute or chronic disease were approached and 458 subjects gave consent; a response rate of 70.5%. Methods Face-to-face interviews were based on a questionnaire that included variables such as socio-demographic information, assessment of non-dietary covariates, assessment of dietary intake, vitamin D intake, type of feeding, clinical manifestations and laboratory investigations. The subjects' health status was assessed by medical conditions, family history, body mass index, past or present clinical manifestations, 25-hydroxy vitamin D, calcium, alkaline phosphates, phosphorus, HbA1C, Parathyroid Hormone (PTH), magnesium and creatinine analysis. Results The study revealed that vitamin D deficiency was highly prevalent in Qatari adolescents (11-16 years old; 61.6%), followed by the 5-10 year olds (28.9%) and those below 5 years old (9.5%). Vitamin D deficiency increased with age and there was a significant difference between vitamin D-deficient and normal children in their age groups (P = 0.013). The body mass index was significantly lower in vitamin D-deficient children (19.6 +/- 3.6; P = 0.019). A family history of vitamin D deficiency was more frequent in children with vitamin D deficiency (33.7%) than in normal children (24.5%). Most of the vitamin D-deficient children had no physical activity (60.6%) and no exposure to sunlight (57.5%). There was a significant difference between both groups in terms of family history of vitamin D deficiency, physical activity, exposure to sunlight and duration of time spent outside under the sun (P<0.05). The mean values of vitamin D serum concentration, calcium, alkaline phosphates, and phosphorus were very low in vitamin D-deficient children. Vitamin D-deficient children had a very poor diet for vitamin D (cod liver oil, 56.5%; milk fortified with vitamin D, 27.3%; fortified food, 24.1%; and seafood, 5.7%) compared with normal children. Fractures (P = 0.006), delayed milestones (P = 0.013), rickets (P = 0.017) and gastroenteritis (P = 0.020) were significantly higher in vitamin D-deficient children. Conclusion The study findings revealed that Qatari children are at high risk for vitamin D deficiency. Lack of exposure to sunlight, outdoor activities under the sun, and physical activity and vitamin D intake are the main associated factors for vitamin D deficiency in the young population of Qatar. Breast-fed infants need to take vitamin D supplements for a longer period.