Reduced Spinal Bone Mineral Density in Adolescents of an Ultra-Orthodox Jewish Community in Brooklyn

Abstract

Objectives. Bone mass increases throughout childhood, with maximal bone mass accrual rate occurring in early to mid-puberty and slowing in late puberty. Prevention of osteoporosis and its morbidities depends primarily on the establishment of adequate peak bone mass. Physical activity, calcium intake, and vitamin D stores (from sunlight conversion of precursors of vitamin D and to a lesser degree from dietary intake) are vital determinants of bone mineral density (BMD). BMD is further controlled by genetic and environmental factors that are poorly understood. Observance of ultra-Orthodox Jewish customs may have a negative effect on the factors that promote bone health, and there have been anecdotal reports of higher fracture rates in this population. The ultra-Orthodox Jewish lifestyle encourages scholarly activity in preference to physical activity. Additionally, modest dress codes and inner-city dwelling reduce sunlight exposure. Orthodox Jews do not consume milk products for 6 hours after meat ingestion, leading to potentially fewer opportunities to consume calcium. Foods from the milk group are some of the best sources of dietary calcium. Our aims are to examine BMD in a group of healthy ultra-Orthodox Jewish adolescents in an urban community and to attempt to correlate it to physical activity and dietary factors. Design and Methods. We recruited 50 healthy, ultra-Orthodox Jews, ages 15 to 19 years (30 males and 20 females). None were taking corticosteroids or had evidence of malabsorption. All girls were postmenarchal and nulliparous. Pubic hair Tanner stage for boys and breast Tanner stage for girls were determined. Weight and height standard deviation scores were calculated. Calcium, phosphorus, protein, vitamin D, and calorie intake were assessed using a comprehensive food questionnaire referring to what has been eaten over the last year. Hours per week of weight-bearing exercise and walking were determined. Serum levels of calcium, intact parathyroid hormone (PTH), 25 hydroxyvitamin D (25[OH]D) and 1,25 dihydroxyvitamin D (1,25[OH]2D) were measured. Lumbar spine (L) BMD was assessed by dual energy radiograph absorptiometry. The pediatric software supplied by Lunar Radiation Corporation, which contains gender- and age-specific norms, provided az score for the lumbar BMD for each participant. L2 to L4 bone mineral apparent density (BMAD) was calculated from L2 to L4 BMD. Results. BMD of L2 to L4 was significantly decreased compared with age/sex-matched normative data: mean zscore was −1.25 ± 1.25 (n = 50). The mean L2 to L4 BMD z score ± standard deviation was −1.71 ± 1.18 for boys and −0.58 ± 1.04 for girls. Eight boys (27%) had L2 to L4 BMD z scores <−2.5, which defines osteoporosis in adulthood. Twenty-seven adolescents (54%), 16 boys and 11 girls, had Tanner stage V. Two participants (4%) had delayed development of Tanner stage V. Mean consumption of calcium by participants under 19 years old was 908 ± 506 mg/day (n = 46), which is lower than the adequate intake of 1300 mg/day for this age. The consumption of phosphorus was 1329 ± 606 mg/day, and the consumption of vitamin D was 286 ± 173 IU/day (n = 50). The mean serum 25(OH)D level was 18.4 ± 7.6 ng/mL, and the mean serum 1,25(OH)2D level was 71.1 ± 15.7 pg/mL (n = 50). Boys had significantly higher serum levels of 1,25(OH)2D than did girls (74.9 ± 16.46 pg/mL vs 65.25 ± 12.8 pg/mL, respectively). The serum levels of PTH, calcium, and protein were (mean ± standard deviation): 33 ± 16 pg/mL, 9.5 ± 0.69 mg/dL, and 7.8 ± 0.6 g/dL, respectively (n = 50). L2 to L4 BMD z score had positive correlation with walking hours (r = 0.4). L2 to L4 BMDz score had negative correlation with serum level of 1,25(OH)2D )r = −0.33;n = 50). We could not find significant correlation between L2 to L4 BMD z scores for the entire cohort and any of calcium, vitamin D, phosphorus, or protein intake. However, the L2 to L4 BMD z scores of boys had positive correlation with calcium, phosphorus, and protein intake (r = 42, r = 44, and r = 43, respectively). After adjustment for Tanner stage, boys who had Tanner stage V (n = 16) had stronger positive correlation between L2 to L4 BMD z scores and calcium and protein intake (r = 0.55 and r = 0.57, respectively), as was the correlation between L2 to L4 BMDz score and weight-bearing activity and walking hours (r = 0.77 and r = 0.72, respectively; n = 16). By multiple regression analysis with stepwise selection, sex, walking hours, weight-standard deviation scores, and serum PTH predicted 54% of the variability in L2 to L4 BMD z score. Sex, walking hours, and age predicted 65% of the variability in L2 to L4 BMAD. Conclusions. Lumbar BMD is significantly decreased in ultra-Orthodox Jewish adolescents living in an urban community. Boys had profoundly lower spinal BMD than did girls. Previous studies have introduced estrogen as a critical factor in bone mineralization. However, the role of estrogen is still controversial. Our investigation of the significant determinants of BMD proved that sex is an important predictor of z score in this group, which may indicate the importance of sex hormones. Walking activity was positively associated with L2 to L4 BMDz score and was a significant predictor of L2 to L4 BMDz score and L2 to L4 BMAD. Additional studies are needed to investigate whether walking activity is lacking or is a causal factor of low BMD. The high normal levels of 1,25(OH)2D may represent a compensatory mechanism to absorb more calcium from the intestine, and the low normal 25(OH)D levels may represent relatively poor total body stores of vitamin D in this group of adolescents. This group is at great risk for the morbidities of poor bone health if no bone mineral recovery happens later in their life. We encourage additional longitudinal studies to evaluate the bone mineral status of the elder generation of this community and possible interventions that will lead to improved BMD. We recommend an increase in calcium intake to reach the adequate intake and an increase in walking activity. However, our study provides no evidence that following these recommendations will improve the BMD of this particular population.