Osteoporos Int (2015) 26:653–662 DOI 10.1007/s00198-014-2918-8
ORIGINAL ARTICLE
Peak-bone-mass development in young adults: effects of study program related levels of occupational and leisure time physical activity and exercise. A prospective 5-year study W. Kemmler & M. Bebenek & S. von Stengel & J. Bauer
Received: 5 July 2014 / Accepted: 24 September 2014 / Published online: 7 October 2014 # International Osteoporosis Foundation and National Osteoporosis Foundation 2014
Abstract Summary Young adulthood is characterized by profound lifestyle changes. This study suggests that reduction of sport or exercise, induced by alteration of the occupational situation, negatively impacts generation/maintenance of peak bone mass. In order to compensate occupational-related reductions of physical activity, workplace exercise programs will be helpful. Introduction Only few studies have determined the effect of physical activity or physical exercise on bone mineral density (BMD) in the period of late skeletal maturation, i.e. around peak bone mass. The aim of this article was to determine the long-term effect of different levels of physical activity and exercise directly and indirectly derived by occupation during young adulthood. Methods Sixty-one male and female dental students (DES) and 53 male and female sport students (SPS) 21±2 years old were accompanied over the course (4.8±0.5 years) of their study program. BMD at the lumbar spine (LS), hip, and whole body (WB) were determined using dual-energy X-ray absorptiometry. Results Parameters of physical activity increased nonsignificantly in both groups with no relevant differences between the groups. Indices of exercise, however, increased significantly in the SPS group while a significant decrease was assessed for the DES group. Independent of gender, BMD of the SPS increased significantly (p≤0.007) at all skeletal sites (LS, 2.4±3.9 %; hip, 1.6±3.5 %; WB, 1.8±2.8 %) while W. Kemmler (*) : M. Bebenek : S. von Stengel Institute of Medical Physics, Friedrich-Alexander University Erlangen-Nuremberg, Henkestrasse 91, 91052 Erlangen, Germany e-mail: [email protected] J. Bauer Institute of Dentistry, University-Hospital, Erlangen-Nuremberg, Erlangen, Germany
BMD of the DES remained unchanged at LS (−0.6±4.4 %, p=0.432) and WB (0.5±1.9 %, p=0.092) but decreased significantly at the hip (−1.9±4.3 %, p=0.010). BMD-changes at LS, hip, and WB differ significantly between SPS and DES (p≤0.017). Results remained unchanged after adjusting for baseline BMD-values that differed (p=0.030 to p=0.082) in favor of the SPS group. Conclusion Changes of exercise levels directly or indirectly caused by occupational factors during young adulthood significantly affected generation and/or maintenance of peak bone mass. Compensatory exercise is thus highly relevant for bone health of young adults. Keywords Bone mineral density . Exercise . Occupation . Peak bone mass . Physical activity
Introduction Physical activity and exercise during childhood and adolescence enhance peak bone mass (PBM) [1–3] and may thus reduce the risk of osteoporosis and osteoporosis-related fractures in later life [4–6]. Since the most prominent bone mineral accrual occurs during the period of accelerated growth, the potential of exercise to further maximize bone accrual may be exceptionally high during this period [1, 7]. Indeed, the large amount of exercise studies that address childhood and adolescence (review in [1–3, 7]) confirmed the outstanding osteogenic effect of exercise during the growth period. On the other hand, the effect of exercise slightly before, during, or slightly after the period of skeletal maturation and PBM [8] was scarcely addressed [1]. With respect to physical activity, the period of young adulthood (≈17–22 years) is characterized by profound life style changes due to the start of military service, social year, university studies, or regular occupation with their specific demands and corresponding effects on bone [9]. With
654
some exceptions, however, our modern, automated working environment does not generate relevant levels of physical strain. Furthermore, due to occupational stress and time constraints, a corresponding compensation by leisure time activities becomes much more difficult. This appraisal was confirmed by epidemiologic data that demonstrate that sport participation in Germany significantly decreased by one third from the period of 18–19 to 20–29 years [10]. This early shift towards lower physical activity may negatively affect bone with respect to its complete formation and/or maintenance. Thus, the aim of the present study was to determine changes of physical activity and exercise in two university study programs with different demands and to evaluate the corresponding impact on bone. On order to realize this aim, two university study programs, dentistry, which is known to be a very stressful degree course with low amounts of physical activity [11, 12] and sport science, with its high volume and intensity of exercise, were compared over the entire period through to graduation. Our hypotheses were that (H1) changes of bone mineral density differ significantly between the groups with (H2) further significant increases of bone mineral density (BMD) in the sport student cohort and (H3) significant decreases among the dental students at all the skeletal sites assessed.
Materials and methods The present contribution was part of a project that focuses on the effect of work-related activity or inactivity on health risk factors. This article focuses on the musculoskeletal study endpoint. The study was conducted by the Institute of Medical Physics and the Institute of Dentistry, Friedrich Alexander-University Erlangen-Nuremberg (FAU), Germany. The study protocol was approved by the ethics committee of the FAU (Ethik-Antrag 3674), Germany, and the Federal Institute of Radiation Protection (Z5-22462/22007-041). All the study participants gave written informed consent. The study was fully registered under www. clinicaltrials.gov (NCT00521235). Trial design This study was a prospective 5-year observational study conducted at the University of Erlangen-Nuremberg, Southern Germany. Participants Based on lists of study starters of the years 2007 and 2008 for male and female dentistry and sport science students, 100 study starters, each from the disciplines “dentistry” and “sport sciences” selected by computer-generated random lists
Osteoporos Int (2015) 26:653–662
designed by the primary investigator (W.K.), were contacted by mail. After detailed personal study information, 121 out of 157 basically interested subjects were still willing to participate and were further tested for eligibility. Eight subjects had to be rejected due to our exclusion criteria of (a) diseases/ medication affecting bone metabolism, (b) pregnancy, (c) intended change of the study program or location, (d) age ≥30 years; thus 114 eligible subjects (dental students (DES), n=61 vs. sport students (SPS), n=53) were finally included in the study (Fig. 1). Table 1 gives baseline characteristics of both groups. The study took place at the Friedrich Alexander-University Erlangen-Nuremberg (FAU), Bavaria, Germany, during November 2007 and July 2013. Baseline test were performed during the initial 6 weeks of the first semester of the student. Intervention Study contents and volume were exactly prescribed for both study programs in the corresponding protocols for dentistry and sport sciences. The regular study period of dentistry averaged 11 semesters (including audit period) for completing the course. The study protocol prescribed a large number of obligatory and facultative lectures, colloquia, tutorial, workshops, clinical placements, and examinations that average up to 32–36 h/week/ semester. During the “semester breaks,” there were no lectures and tutorials; however, compensatory dentistry work was increased, and the key examinations were held during those 2-month periods. Since not all the study components were obligatory and the amount of preparation for examinations varied between the students, it is difficult to list the exact amount of time directly or indirectly (preparation time for lectures and examinations) related to the dentistry study program. However, based on individual questionnaires provided after the fourth semester and the end of the study program, we determined an average weekly workload directly or indirectly related to the dentistry course of 34±10 h/week (29–43 h/ week) predominately in a sitting, less frequent in a standing position. The regular study period of sport science (as a secondaryschool teaching qualification in Bavaria) averaged nine semesters (including audit period). Beside theory, 1,050 obligatory hours of practical sport application are required by the study protocol (i.e., Ø 7.8 h/week). Preparation for sports practice, corresponding tests and leisure time sports activity increase this amount up to 11.9±2.4 h/week (range, 8–17 h/ week). With respect to exercise, altogether 12 different disciplines have to be taken. Obligatory core disciplines were gymnastics, track and field athletics, swimming, dancing, soccer, volleyball, handball, basketball, and skiing (downhill). Additionally, subjects have to opt for four more disciplines (out of martial arts, racket games, water-sports, biking,
Osteoporos Int (2015) 26:653–662
655
Fig. 1 Extended “flow-chart” of the study
hockey/ice-hockey, etc.). Although courses did not take place during the semester breaks, the total amount of exercise remained high (i.e., 6±3 h/week) due to increased leisure time
sports activity. In summary, with respect to type, mode, and the composition of loading parameters, this “intervention” can be considered as an optimal osteoanaboleous stimulus.
Table 1 Baseline characteristics of the study participants Variable (at baseline)
Sport-science (SPS)
Dentistry (DES)
Gender Age [years] Body height [cm] Body weight [kg] White, Caucasian race [%] Body fat [%] Activity intensity index [hours/week]a Exercise index [min/week]a Active in sports competitions [%] Maximum oxygen uptake [ml/min/kg]b
Female, n=29 20.1±2.1 167.5±6.4 62.5±7.4 97 23.8±4.2 30±10 221±115 100 57.4±5.5
Male, n=24 20.6±1.9 181.0±5.5 72.8±6.6 92 12.5±3.1 28±9 270±126 100 46.1±4.2
Female, n=33 20.5±2.5 169.2±7.1 59.8±6.4 97 26.3±3.9 32±9 109±65 21 52.0±8.8
Male, n=28 21.1±3.1 181.3±7.0 75.5±8.7 89 16.7±4.0 27±11 123±71 25 42.2±54.8
Daylight exposure summer [min/day] Daylight exposure winter [min/day]
203±71 66±29
217±79 69±35
121±69 31±33
110±53 34±36
a
According to the questionnaire provided by Kemmler et al. [16]
b
As assessed by breath using an open spirometric system during stepwise ergometer test to a voluntary maximum
656
Osteoporos Int (2015) 26:653–662
Indeed, a recent study [13, 14] with sports science students demonstrated significantly increased BMD at most skeletal site compared with runners, climbers, or untrained controls.
Outcome The primary study outcome addressed in this article was the effect of occupational-induced changes of physical activity and exercise generated by two different study programs (dentistry vs. sports sciences) on
Bone mineral density BMD was assessed with DXA (QDR 4500, discovery upgrade, Hologic Inc., Bedford, USA) twice, at baseline and after 4.8±0.5 years, using the whole body standard protocol specified by the manufacturer. Based on the whole body (WB) DXA standard protocol described above, BMD at the lumbar spine (LS) and the hip region of interest were segmented and analyzed. Long-term coefficient of variation (2007–2013) of our device as determined by phantom assessment was
ORIGINAL ARTICLE
Peak-bone-mass development in young adults: effects of study program related levels of occupational and leisure time physical activity and exercise. A prospective 5-year study W. Kemmler & M. Bebenek & S. von Stengel & J. Bauer
Received: 5 July 2014 / Accepted: 24 September 2014 / Published online: 7 October 2014 # International Osteoporosis Foundation and National Osteoporosis Foundation 2014
Abstract Summary Young adulthood is characterized by profound lifestyle changes. This study suggests that reduction of sport or exercise, induced by alteration of the occupational situation, negatively impacts generation/maintenance of peak bone mass. In order to compensate occupational-related reductions of physical activity, workplace exercise programs will be helpful. Introduction Only few studies have determined the effect of physical activity or physical exercise on bone mineral density (BMD) in the period of late skeletal maturation, i.e. around peak bone mass. The aim of this article was to determine the long-term effect of different levels of physical activity and exercise directly and indirectly derived by occupation during young adulthood. Methods Sixty-one male and female dental students (DES) and 53 male and female sport students (SPS) 21±2 years old were accompanied over the course (4.8±0.5 years) of their study program. BMD at the lumbar spine (LS), hip, and whole body (WB) were determined using dual-energy X-ray absorptiometry. Results Parameters of physical activity increased nonsignificantly in both groups with no relevant differences between the groups. Indices of exercise, however, increased significantly in the SPS group while a significant decrease was assessed for the DES group. Independent of gender, BMD of the SPS increased significantly (p≤0.007) at all skeletal sites (LS, 2.4±3.9 %; hip, 1.6±3.5 %; WB, 1.8±2.8 %) while W. Kemmler (*) : M. Bebenek : S. von Stengel Institute of Medical Physics, Friedrich-Alexander University Erlangen-Nuremberg, Henkestrasse 91, 91052 Erlangen, Germany e-mail: [email protected] J. Bauer Institute of Dentistry, University-Hospital, Erlangen-Nuremberg, Erlangen, Germany
BMD of the DES remained unchanged at LS (−0.6±4.4 %, p=0.432) and WB (0.5±1.9 %, p=0.092) but decreased significantly at the hip (−1.9±4.3 %, p=0.010). BMD-changes at LS, hip, and WB differ significantly between SPS and DES (p≤0.017). Results remained unchanged after adjusting for baseline BMD-values that differed (p=0.030 to p=0.082) in favor of the SPS group. Conclusion Changes of exercise levels directly or indirectly caused by occupational factors during young adulthood significantly affected generation and/or maintenance of peak bone mass. Compensatory exercise is thus highly relevant for bone health of young adults. Keywords Bone mineral density . Exercise . Occupation . Peak bone mass . Physical activity
Introduction Physical activity and exercise during childhood and adolescence enhance peak bone mass (PBM) [1–3] and may thus reduce the risk of osteoporosis and osteoporosis-related fractures in later life [4–6]. Since the most prominent bone mineral accrual occurs during the period of accelerated growth, the potential of exercise to further maximize bone accrual may be exceptionally high during this period [1, 7]. Indeed, the large amount of exercise studies that address childhood and adolescence (review in [1–3, 7]) confirmed the outstanding osteogenic effect of exercise during the growth period. On the other hand, the effect of exercise slightly before, during, or slightly after the period of skeletal maturation and PBM [8] was scarcely addressed [1]. With respect to physical activity, the period of young adulthood (≈17–22 years) is characterized by profound life style changes due to the start of military service, social year, university studies, or regular occupation with their specific demands and corresponding effects on bone [9]. With
654
some exceptions, however, our modern, automated working environment does not generate relevant levels of physical strain. Furthermore, due to occupational stress and time constraints, a corresponding compensation by leisure time activities becomes much more difficult. This appraisal was confirmed by epidemiologic data that demonstrate that sport participation in Germany significantly decreased by one third from the period of 18–19 to 20–29 years [10]. This early shift towards lower physical activity may negatively affect bone with respect to its complete formation and/or maintenance. Thus, the aim of the present study was to determine changes of physical activity and exercise in two university study programs with different demands and to evaluate the corresponding impact on bone. On order to realize this aim, two university study programs, dentistry, which is known to be a very stressful degree course with low amounts of physical activity [11, 12] and sport science, with its high volume and intensity of exercise, were compared over the entire period through to graduation. Our hypotheses were that (H1) changes of bone mineral density differ significantly between the groups with (H2) further significant increases of bone mineral density (BMD) in the sport student cohort and (H3) significant decreases among the dental students at all the skeletal sites assessed.
Materials and methods The present contribution was part of a project that focuses on the effect of work-related activity or inactivity on health risk factors. This article focuses on the musculoskeletal study endpoint. The study was conducted by the Institute of Medical Physics and the Institute of Dentistry, Friedrich Alexander-University Erlangen-Nuremberg (FAU), Germany. The study protocol was approved by the ethics committee of the FAU (Ethik-Antrag 3674), Germany, and the Federal Institute of Radiation Protection (Z5-22462/22007-041). All the study participants gave written informed consent. The study was fully registered under www. clinicaltrials.gov (NCT00521235). Trial design This study was a prospective 5-year observational study conducted at the University of Erlangen-Nuremberg, Southern Germany. Participants Based on lists of study starters of the years 2007 and 2008 for male and female dentistry and sport science students, 100 study starters, each from the disciplines “dentistry” and “sport sciences” selected by computer-generated random lists
Osteoporos Int (2015) 26:653–662
designed by the primary investigator (W.K.), were contacted by mail. After detailed personal study information, 121 out of 157 basically interested subjects were still willing to participate and were further tested for eligibility. Eight subjects had to be rejected due to our exclusion criteria of (a) diseases/ medication affecting bone metabolism, (b) pregnancy, (c) intended change of the study program or location, (d) age ≥30 years; thus 114 eligible subjects (dental students (DES), n=61 vs. sport students (SPS), n=53) were finally included in the study (Fig. 1). Table 1 gives baseline characteristics of both groups. The study took place at the Friedrich Alexander-University Erlangen-Nuremberg (FAU), Bavaria, Germany, during November 2007 and July 2013. Baseline test were performed during the initial 6 weeks of the first semester of the student. Intervention Study contents and volume were exactly prescribed for both study programs in the corresponding protocols for dentistry and sport sciences. The regular study period of dentistry averaged 11 semesters (including audit period) for completing the course. The study protocol prescribed a large number of obligatory and facultative lectures, colloquia, tutorial, workshops, clinical placements, and examinations that average up to 32–36 h/week/ semester. During the “semester breaks,” there were no lectures and tutorials; however, compensatory dentistry work was increased, and the key examinations were held during those 2-month periods. Since not all the study components were obligatory and the amount of preparation for examinations varied between the students, it is difficult to list the exact amount of time directly or indirectly (preparation time for lectures and examinations) related to the dentistry study program. However, based on individual questionnaires provided after the fourth semester and the end of the study program, we determined an average weekly workload directly or indirectly related to the dentistry course of 34±10 h/week (29–43 h/ week) predominately in a sitting, less frequent in a standing position. The regular study period of sport science (as a secondaryschool teaching qualification in Bavaria) averaged nine semesters (including audit period). Beside theory, 1,050 obligatory hours of practical sport application are required by the study protocol (i.e., Ø 7.8 h/week). Preparation for sports practice, corresponding tests and leisure time sports activity increase this amount up to 11.9±2.4 h/week (range, 8–17 h/ week). With respect to exercise, altogether 12 different disciplines have to be taken. Obligatory core disciplines were gymnastics, track and field athletics, swimming, dancing, soccer, volleyball, handball, basketball, and skiing (downhill). Additionally, subjects have to opt for four more disciplines (out of martial arts, racket games, water-sports, biking,
Osteoporos Int (2015) 26:653–662
655
Fig. 1 Extended “flow-chart” of the study
hockey/ice-hockey, etc.). Although courses did not take place during the semester breaks, the total amount of exercise remained high (i.e., 6±3 h/week) due to increased leisure time
sports activity. In summary, with respect to type, mode, and the composition of loading parameters, this “intervention” can be considered as an optimal osteoanaboleous stimulus.
Table 1 Baseline characteristics of the study participants Variable (at baseline)
Sport-science (SPS)
Dentistry (DES)
Gender Age [years] Body height [cm] Body weight [kg] White, Caucasian race [%] Body fat [%] Activity intensity index [hours/week]a Exercise index [min/week]a Active in sports competitions [%] Maximum oxygen uptake [ml/min/kg]b
Female, n=29 20.1±2.1 167.5±6.4 62.5±7.4 97 23.8±4.2 30±10 221±115 100 57.4±5.5
Male, n=24 20.6±1.9 181.0±5.5 72.8±6.6 92 12.5±3.1 28±9 270±126 100 46.1±4.2
Female, n=33 20.5±2.5 169.2±7.1 59.8±6.4 97 26.3±3.9 32±9 109±65 21 52.0±8.8
Male, n=28 21.1±3.1 181.3±7.0 75.5±8.7 89 16.7±4.0 27±11 123±71 25 42.2±54.8
Daylight exposure summer [min/day] Daylight exposure winter [min/day]
203±71 66±29
217±79 69±35
121±69 31±33
110±53 34±36
a
According to the questionnaire provided by Kemmler et al. [16]
b
As assessed by breath using an open spirometric system during stepwise ergometer test to a voluntary maximum
656
Osteoporos Int (2015) 26:653–662
Indeed, a recent study [13, 14] with sports science students demonstrated significantly increased BMD at most skeletal site compared with runners, climbers, or untrained controls.
Outcome The primary study outcome addressed in this article was the effect of occupational-induced changes of physical activity and exercise generated by two different study programs (dentistry vs. sports sciences) on
Bone mineral density BMD was assessed with DXA (QDR 4500, discovery upgrade, Hologic Inc., Bedford, USA) twice, at baseline and after 4.8±0.5 years, using the whole body standard protocol specified by the manufacturer. Based on the whole body (WB) DXA standard protocol described above, BMD at the lumbar spine (LS) and the hip region of interest were segmented and analyzed. Long-term coefficient of variation (2007–2013) of our device as determined by phantom assessment was
