Einfluss verschiedener Lebensstilfaktoren auf die Knochenmasse von Kindern und Jugendlichen: Möglichkeiten der Gesundheitsförderung im Setting Schule

Background Osteoporosis and related secondary diseases are one of the biggest health problems in the Western industrialized nations. The accrual of bone mass occurs mainly in childhood and youth, until it reaches the peak bone mass of the adult skeleton at the end of the third decade of life. Peak bone mass depends not only on genetic factors but different lifestyle factors such as physical activity, nutrition and consumption of stimulants. A reduced peak bone mass is one of the key risk factors for the occurrence of osteoporosis in later life. Recent studies suggest that children and adolescents do not reach their peak bone mass due to an unfavourable lifestyle. Methods Against this background, 486 healthy students of Schwaebisch Gmuend were investigated in terms of bone density, body composition and their nutritional and physical activity behaviour. Bone mass (stiffness index, SI) was determined by calcaneal quantitative ultrasonometry (Achilles Insight). Body weight and body height were measured standardized. Fat-free mass and fat mass were measured by bioelectrical impedance analysis (BIA) using the formula of Plachta-Danielzik et al. (2012). As a measure of physical activity the physical activity level (PAL) was used. With the help of a food frequency questionnaire food intake was assessed and a bone healthy eating index (BHEI) was developed. Puberty, time spent outdoors, smoking habits, oral contraceptive use, and socio-demographic and socio-economic data were assessed using a standardized questionnaire. Results Mean stiffness index for boys (age: 13,3 ± 1,7 years; BMI: 19,3 ± 3,3 kg/m2) is 94 ± 19, and for girls (age: 13,1 ± 1,9 years; BMI: 20,2 ± 4,7 kg/m2) 94 ± 18. Fat-free mass and fat mass for boys are on average 41,7 ± 10,4 kg and 9,8 ± 5,5 kg, and for girls 37,5 ± 7,2 and 13,8 ± 8,7, respectively. PAL is for boys and girls on average 1,53 ± 0,15 and 1,41 ± 0,09, respectively. Mean BHEI is for boys 56 ± 16 and for girls 60 ± 13. SI is significant positively correlated with age, body weight, BMI, absolute fat-free mass, PAL and puberty in boys and girls. In boys, SI is significant positively correlated with educational background. Significant negative correlation can be found in girls between SI and percentage of fat-free mass as well as intake of contraceptives. SI does not correlate significantly with BHEI, food intake, migration background, time spent outside/outdoors and vitamin D-intake in the first year of life in boys and girls. In multiple regression analysis, age, body composition, sex and physical activity proved to be significant predictors of SI: SI = 2,81 + 3,14 * age [yrs] + 0,60 * FFM [kg] + 5,71 * sex + 16,07 * PAL [0 =male, 1 = female] (r² = 0,36; SE = 14,81). Fat mass, time spent outdoors, BHEI, and smoking have no effect on SI. Boys with low bone mass are often affected by underweight, girls with low bone mass drink more sodas/lemonades compared to students with high bone mass. With regard to food intake and physical activity, the questionnaire can be considered reproducible. Conclusion Due to the results of the present study, activity behaviour has an essential influence on bone mass of children and adolescents taking into account body composition, gender and age.