الفهرس 
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Abstract
M
any diseases deleteriously affect bone density and bone mass accrual causing osteoporosis which is a public health concern that has extensive physical and psychological consequences. It is no longer considered age dependent, which means it can affect children and adolescents. It is largely preventable by avoiding risk factors, early diagnosis and intervention. The NIH consensus conference in 2000 stated that bone mineral accrual during childhood is a major determinant of osteoporosis risk later in life.
Recent studies aim to determine the effect of age, sex, ethnicity and puberty on bone mineral accrual, also to study the contribution of modifiable factors including calcium intake, physical activity, sunlight exposure and socio-economic status on BMD. Also setting a reference range of normal values of BMD and BMC at different skeletal sites in different age groups is particularly important in following up children at risk for osteoporosis as those on long term treatment with corticosteroids.
According to International Society of Clinical Densitometry (ISCD), DXA is the preferred method for assessing BMD and BMC in children due to its short scan times, low radiation dose, low cost and good precision.
The purpose of our study was to provide reference data for DXA measurements of BMD and BMC at multiple skeletal sites, and to study the relation of multiple factors affecting bone mineral accrual.
This cross sectional study included 20 Egyptian male children, recruited from the pediatric outpatient clinic of Pediatric hospital, Ain-Shams University. Their mean age was 13.4 ± 0.36 years.
All were subjected to detailed medical history including assessment of daily dietary calcium intake by a detailed food frequency questionnaire (FFQ) (three days recall) and data was analyzed according to the Egyptian food composition tables (NNI, 2006). Assessment of duration of sunlight exposure (hours/week) and percentage of body area exposed according to the Lund and Browder chart (Hettiaratchy and Papini, 2004), assessment of duration of physical activity (hours/week) and assessment of socioeconomic status according to the criteria of (El-Bohy, 1988) were done.
They were also subjected to general and systemic examinations to ensure that the sample reflects healthy, normally developing children, with no previous medical history that is known to affect growth or bone mineral accrual. Anthropometric measurements were done including weight, height, BMI and calculating their SDS’s. Pubertal stage was determined by physical examination performed by an expert endocrinologist using an orchidometer with stages of pubic hair and testicular volume being evaluated according to the criteria of Tanner (Tanner et al., 1976). Serum levels of calcium, phosphorus and alkaline phosphatase were measured via blood samples.
Then assessment of BMD of whole body, lumbar spine, left femoral neck and whole body BMC, lean body mass and fat mass using Hologic (Horizon Wi) DXA scanner.
The mean and SD for our DXA parameters were calculated. The mean value of whole body BMD was 0.87 ± 0.06 gm/cm2, the mean value of lumbar spine BMD was 0.67 ± 0.06 gm/cm2 and the mean value of femoral neck BMD was 0.78 ± 0.07 gm/cm2. The mean value of subtotal body BMD was 0.81 ± 0.06 gm/cm2. As regard body composition, the mean value of whole body BMC was 1267.96 ± 165.86 gm, the mean value of whole body fat was 13093.08 ± 4928.62 gm, the mean value of lean body mass was 29809.35 ± 3165.48 gm and that of fat percentage was 29.69 ± 6.03 gm.
The mean value of calcium intake in our study was 1425.40 ± 176.73 mg/day. Our results showed a significant positive correlation between calcium intake and each of whole body BMD and its Z-score, subtotal BMD, lumbar spine BMD and its Z-score, LSBMAD, femoral neck BMD and its Z-score, whole body BMC and lean body mass. A significant negative correlation between calcium level in blood and each of whole body fat and fat percentage was found.
The mean value of BMI in our study was 18.94 ± 2.59 kg/m2. Weight and BMI were major determinants of BMD in our study with highly significant associations between weight SDS and BMI SDS and all DXA parameters except FNBMAD.
The mean height SDS in our study was -0.62 ± 0.54. There were significant positive correlations between height SDS and lumbar spine BMD and its Z-score, LSBMAD, femoral neck Z-score, whole body BMC, whole body fat and fat percentage.
No significant correlation was found between sunlight exposure, percentage of body area exposed, physical activity or any of the DXA parameters.
Socio-economic level was found to be significantly correlated with whole body BMD and its Z-score, subtotal BMD, lumbar spine BMD and its Z-score, LSBMAD, femoral neck BMD and its Z-score, whole body fat and fat percentage