Elsevier

Bone

Volume 45, Issue 5, November 2009, Pages 925-930
Bone

Extracurricular physical activity participation modifies the association between high TV watching and low bone mass

https://doi.org/10.1016/j.bone.2009.07.084Get rights and content

Abstract

Objectives

To examine whether different sedentary behaviours are associated with the risk of low bone mineral content in adolescents, and if so, whether extracurricular physical-sporting activity influences this association.

Materials and methods

A total of 277 adolescents from Zaragoza (168 females and 109 males) aged 13.0–18.5 yr within frame work of the multicentre AVENA study participated in this study. Bone mineral content (BMC), lean mass, and fat mass were measured with DXA. Physical activity and sedentary independent variables: participation in extracurricular physical-sporting activity (PA), h/d of television watching, playing video/computer games during school days and on weekend days and doing homework/studying. They all were assessed by questionnaire. The main outcome was low BMC, as defined by BMC Z-score for age and sex < percentile 10.

Logistic regression was used to test the interaction and association of PA and sedentary variables with low BMC, after controlling for confounders like height, maturational status or lean mass.

Results

Among the sedentary variables studied, only television watching  3 h/d was associated with an increased risk for low BMC in males (OR, 95% CI: 7.01, 1.73 to 28.40), after controlling for sexual maturation. When PA was in the models, television watching was not any longer associated with low BMC, while PA was so (OR, 95% CI: 0.23, 0.09 to 0.55). Involvement in such activity reduced the risk of low bone mass by 76% (P < 0.01) independently of body mass, height and fat mass, but not of the lean mass.

Conclusion

Watching television for 3 or more h/d seems to be associated with an increased risk for low BMC in male adolescents. However, this association is mediated by participation in PA, suggesting that negative consequences of excessive television watching on adolescent bone health could be counteracted by sport participation. Longitudinal data and randomized controlled trials will confirm or contrast our findings.

Introduction

Osteoporosis is a matter for concern all over the world [1]. Bone mass tends to track along a percentile, which means that if an individual has low bone mass at one point of his life, he or she will probably have low bone mass later in life [2], unless any intervention is made. In this context, environmental factors may have a substantial impact on peak bone mass [3], [4]; this implies that it is possible to act to increase bone mass. Although that increase can be lost with time [5], it could also be maintained if the demands on bone persist [6], or depending on the intervention made during growth, such as physical exercise [7]. It is, therefore, important to identify those children at risk of low bone mass, and the possible causes of it, since intervention to attain a higher peak of bone mass during growth is possible [7].

Sedentarism is frequently described as an important determinant of low bone mass [8], but the concrete effect of different sedentary behaviours (e.g. television watching, playing videogames, etc.) on bone mass has not been studied in depth. In fact, no studies have looked at the effect of sedentary behaviours on bone mass during adolescence, which is a sensitive period for skeleton development [9]. More research have been however focused on the effect of participating in physical activity and sport on bones during growth [10].

Children and adolescents spend little time participating in sports or physical activities [11], while they devote more time to activities such as watching television (TV) and playing video games [12]. This sedentary lifestyle is supposed to predispose to obesity [13] and may attenuate bone mass accrual, thus increasing the risk for a low bone mineral content (BMC), and perhaps leading to a low peak bone mass [8]. The importance of determining the independent effect of sedentary behaviours on the risk of low bone mass during adolescence is therefore clear, as is the need to search for guidelines for its prevention. In addition, the role of physical activity in the association between sedentary behaviours and BMC is unknown, and needs to be examined for its potential public health implications.

In this study we examined whether different sedentary behaviours were associated with low bone mineral content (BMC) in adolescents and if so, whether extracurricular physical-sporting activity modified these associations.

Section snippets

Population

The complete methodology of the multicentre AVENA study, (Alimentación y Valoración del Estado Nutricional en Adolescentes; in English: Feeding and assessment of nutritional status of Spanish adolescents) performed on Spanish adolescents aged 13–18.5 yr has been described elsewhere [14]. In brief, the multicentre study was performed on Spanish adolescents aged 13–18.5 yr. The population was selected by means of a multiple step, simple random sampling, taking into account first the location

Results

Descriptive for anthropometrics and body composition are displayed in Table 1. Males of 13 yr old had lower body mass, height, BMC and LM than males over 15 yr old (P < 0.05; Table 1). Fourteen yr old males had lower height and BMC than males over 16 yr old, and lower LM than males over 15 yr old (all P < 0.05; Table 1). Compared with females, males showed higher body mass, height, BMC and LM from 14, 15, 15, and 13 yr old respectively; and lower FM from 16 yr old (all P < 0.05; Table 1).

Percentages

Discussion

The main findings of this study are 1) that within sedentary behaviours only TV watching seemed to be associated with higher risk of low BMC in males; and 2) that being involved in extracurricular physical-sporting activity seems to be associated with protective odds for low bone mass due to high TV watching.

Environment and lifestyle explain 15 to 50% of the variability in bone mass [3], [4], so it is important to know which factors stimulate or impair bone accrual. In this regard, osteogenic

Acknowledgments

The AVENA study was supported by the Spanish Ministry of Health (FIS 00/0015), and grants from Panrico S.A., Madaus S.A., and Procter and Gamble S.A. GVR was supported by a grant from DGA (CONSI+D) and CAI (CM 11/07). JPR was supported by a grant from the Cuenca Villoro Foundation. FBO was supported by grants from the Consejo Superior de Deportes (109/UPB31/03, 13/UPB20/04) and Ministerio de Educación y Ciencia de España (AP2004-2745).

The authors wish to thank Prof. Olle Carlsson for his

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