Bone health in children and adolescents: risk factors for low bone density.

Osteoporosis is a common disease that is characterized by low bone mineral density (BMD). Decreased BMD is associated with increased fracture risk. In adults, normal BMD results from the balance between accrual of peak bone mass (PBM) at the end of adolescence, and subsequent bone loss with age. Although environmental factors play a role, hereditary factors are the major contributors (up to 80%) to the variability in PBM. This review examines the effects of genetics, physical activity and immobilization, smoking, chronic diseases and medications, vitamin D, calcium, and various other dietary factors on bone integrity in children, adolescents, and adults.

Physical activity and bone health in children and adolescents.

Bone gain is the greatest during the pubertal years. However, physical activity declines precipitously with age among adolescents (1,2). Therefore, promotion of physical activity in children and adolescents is very important. It is imperative to maximize peak bone mass, so bones remain strong even after losing their density during later life (3). While a number of environmental factors determine the peak bone mass, such as calcium intake and physical activities (4), the latter is more influential as a contributor to the peak bone mass (4). Physical activity is the modifiable factor that can enhance bone accretion if the individual performs regularly. Weight-bearing activity has been shown to increase bone accretion more than non-weight bearing activity. In this article, we review all the physical activities and the exercise regimens that have been documented to be efficient in promoting bone gain in children and adolescents. We also suggest recommended physical activity regimens for children and adolescents in order to maintain and improve bone accretion. In addition, we emphasize participating in regular physical activity and maintaining a healthy lifestyle across the lifespan to maintain optimal bone health.

Subclinical thyroid disorders and cognitive performance among adolescents in the United States.

BACKGROUND: Thyroid hormone plays a crucial role in the growth and function of the central nervous system. The purpose of the study was to examine the relationships between the status of subclinical thyroid conditions and cognition among adolescents in the United States. METHODS: Study sample included 1,327 adolescents 13 to 16 years old who participated in the Third National Health and Nutrition Examination Survey (NHANES III). Serum thyroxine (T4) and thyroid stimulating hormone (TSH) were measured and subclinical hypothyroidism, subclinical hyperthyroidism, and euthyroid groups were defined. Cognitive performance was assessed using the subscales of the Wide Range Achievement Test-Revised (WRAT-R) and the Wechsler Intelligence Scale for Children-Revised (WISC-R). The age-corrected scaled scores for arithmetic, reading, block design, and digit span were derived from the cognitive assessments. RESULTS: Subclinical hypothyroidism was found in 1.7% and subclinical hyperthyroidism was found in 2.3% of the adolescents. Cognitive assessment scores on average tended to be lower in adolescents with subclinical hyperthyroidism and higher in those with subclinical hypothyroidism than the score for the euthyroid group. Adolescents with subclinical hypothyroidism had significantly better scores in block design and reading than the euthyroid subjects even after adjustment for a number of variables including sex, age, and family income level. CONCLUSION: Subclinical hypothyroidism was associated with better performance in some areas of cognitive functions while subclinical hyperthyroidism could be a potential risk factor.

Growth failure in early life: an important manifestation of Turner syndrome.

The goals of this study were to test the hypothesis that girls with Turner syndrome (TS) experience growth failure early in life and to establish model-based normative growth charts for 0- to 8-year-old American girls with TS. Full-term girls with TS who had 5 or more measurements of height obtained during their first 10 years of life prior to initiation of growth hormone, estrogen and/or androgen therapy were eligible for this study. A nonlinear mixed-effects model comprising the first two components of the infancy-childhood-puberty (ICP) model of growth was fitted to the longitudinal height measurements and compared with those of healthy American girls. Height measurements (n = 1,146) from 112 girls with TS (45,X: 57.1%; 45,X/46,XX: 12.5%; 46,X, iso(X): 4.5%, and other: 25.9%) were analyzed. Mean height SDS fell from -0.68 at birth to -1.60 at 1 year, -1.80 at 2 years and -1.95 at 3 years. When compared to controls (676 girls, 4,537 measurements), girls with TS grew more slowly due to three principal factors: a slow growth rate of the infancy component, a slow growth rate at the onset of the childhood component, and delayed onset of the childhood component. Traditional concepts of growth failure in TS should be revised. Physicians should consider the diagnosis of TS in any girl with unexplained failure to thrive or short stature, even in the first 3 years of life.