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Bone growth is most pronounced during adolescence. This study aimed to elucidate the effect of adolescent body build and strength on bone mineral density markers and bone metabolism to help improve bone growth during adolescence and prevent future osteoporosis. From 2009 to 2015, 277 adolescents (125 boys and 152 girls) aged 10/11 and 14/15 took part in the survey. Measurements include fitness/body mass index (e.g., muscle ratio, etc.), grip strength, bone mineral density (osteosonometry index, OSI), and markers of bone metabolism (bone-type alkaline phosphatase and type I collagen cross-linked N) . -terminal peptide). A positive correlation between body size/grip strength and OSI was found in girls aged 10/11 years. In boys aged 14/15 years, all body size/grip strength factors were positively associated with OSI. Changes in body muscle proportions were positively correlated with changes in OSI in both sexes. Height, body muscle ratio and grip strength at 10/11 years of age in both sexes were significantly associated with OSI (positive) and bone metabolism markers (negative) at 14/15 years of age. Adequate physique after 10-11 years of age in boys and up to 10-11 years of age in girls may be effective in increasing peak bone mass.
Healthy life expectancy was proposed by the World Health Organization (WHO) in 2001 as the average length of time a person can lead a healthy lifestyle on their own in their daily lives. In Japan, the gap between healthy life expectancy and average life expectancy is expected to exceed 10 years2. Thus, the “National Movement for Health Promotion in the 21st Century (Healthy Japan 21)” was created to increase healthy life expectancy3,4. To achieve this, it is necessary to delay people’s time for care. Movement syndrome, weakness and osteoporosis5 are the main reasons for seeking medical care in Japan. In addition, control of metabolic syndrome, childhood obesity, frailty and motor syndrome is a measure to prevent the need for care6.
As we all know, regular moderate exercise is essential for good health. To play sports, the motor system, which consists of bones, joints and muscles, must be healthy. As a result, the Japan Orthopedic Association defined “Motion Syndrome” in 2007 as “immobility due to musculoskeletal disorders and [in which] there is a high risk of requiring long-term care in the future”7, and preventive measures have been studied since then. then. However, according to the 2021 White Paper, aging, fractures, and musculoskeletal disorders8 remain the most common causes of care needs in Japan, accounting for a quarter of all care needs.
In particular, fracture-causing osteoporosis is reported to affect 7.9% of men and 22.9% of women over 40 in Japan9,10. Early detection and treatment appears to be the most important way to prevent osteoporosis. Assessment of bone mineral density (BMD) is critical for early detection and treatment. Dual energy X-ray absorption (DXA) has traditionally been used as an indicator for bone evaluation in various radiological modalities. However, fractures have been reported to occur even with high BMD, and in 2000 a National Institutes of Health (NIH)11 consensus meeting recommended bone mass increase as a measure of bone assessment. However, assessing bone quality remains challenging.
One way to assess BMD is by ultrasound (quantitative ultrasound, QUS)12,13,14,15. Studies have also shown that QUS and DXA results are correlated16,17,18,19,20,21,22,23,24,25,26,27. However, QUS is non-invasive, non-radioactive, and can be used to screen pregnant women and children. In addition, it has a clear advantage over DXA, namely that it is removable.
Bone is taken up by osteoclasts and formed by osteoblasts. Bone density is maintained if bone metabolism is normal and there is a balance between bone resorption and bone formation.
Conversely, abnormal bone metabolism results in decreased BMD. Therefore, for early detection of osteoporosis, markers of bone metabolism, which are independent indicators associated with BMD, including markers of bone formation and bone resorption, are used to assess bone metabolism in Japan. The Fracture Intervention Trial (FIT) with a fracture prevention endpoint showed that BMD is a marker of bone formation rather than bone resorption16,28. In this study, markers of bone metabolism were also measured to objectively study the dynamics of bone metabolism. These include markers of bone formation (bone-type alkaline phosphatase, BAP) and markers of bone resorption (cross-linked N-terminal type I collagen peptide, NTX).
Adolescence is the age of peak growth rate (PHVA), when bone growth is rapid and bone density peaks (peak bone mass, PBM) about 20 years ago.
One way to prevent osteoporosis is to increase PBM. However, since the details of bone metabolism in adolescents are unknown, no specific interventions can be suggested to increase BMD.
Therefore, this study aimed to elucidate the effect of body composition and physical strength on bone mineral density and skeletal markers during adolescence, when bone growth is most active.
This is a four-year cohort study from the fifth grade of elementary school to the third grade of junior high school.
Participants included adolescent boys and girls who participated in the Iwaki Health Promotion Project Primary and Secondary Health Survey in the fifth grade of elementary school and the third grade of junior high school.
Four elementary and junior high schools were selected, located in the Iwaki district of Hirosaki City in northern Japan. The survey was conducted in autumn.
From 2009 to 2011, consenting 5th grade students (10/11 years old) and their parents were interviewed and measured. Of the 395 subjects, 361 people took part in the survey, which is 91.4%.
From 2013 to 2015, consenting third-year secondary school students (14/15 year olds) and their parents were interviewed and measured. Of the 415 subjects, 380 people took part in the survey, which is 84.3%.
The 323 participants included individuals with a history of cardiovascular disease, diabetes, dyslipidemia, or hypertension, individuals taking medications, individuals with a history of fractures, individuals with a history of calcaneus fractures, and individuals with missing values ​​in analysis items. Excluded. A total of 277 adolescents (125 boys and 152 girls) were included in the analysis.
The survey components included questionnaires, bone density measurements, blood tests (markers of bone metabolism), and fitness measurements. The survey was conducted during 1 day of elementary school and 1-2 days of secondary school. The investigation lasted 5 days.
A questionnaire was provided in advance for self-completion. Participants were asked to complete questionnaires with their parents or guardians, and the questionnaires were collected on the day of measurement. Four public health experts reviewed the responses and consulted with the children or their parents if they had any questions. Questionnaire items included age, gender, medical history, current medical history, and medication status.
As part of the physical assessment on the day of the study, measurements of height and body composition were taken.
Body composition measurements included body weight, percentage of body fat (% fat), and percentage of body mass (% muscle). Measurements were taken using a body composition analyzer based on the bioimpedance method (TBF-110; Tanita Corporation, Tokyo). The device uses multiple frequencies 5 kHz, 50 kHz, 250 kHz and 500 kHz and has been used in many adult studies29,30,31. The device is designed to measure participants who are at least 110 cm tall and 6 years of age or older.
BMD is the main component of bone strength. BMD assessment was performed by ECUS using a bone ultrasound device (AOS-100NW; Aloka Co., Ltd., Tokyo, Japan). The measurement site was the calcaneus, which was assessed using the Osteo Sono-Assessment Index (OSI). This device measures the speed of sound (SOS) and transmission index (TI), which are then used to calculate OSI. SOS is used to measure calcification and bone mineral density34,35 and TI is used to measure the attenuation of broadband ultrasound, an index of bone quality assessment12,15. OSI is calculated using the following formula:
Thus reflecting the characteristics of SOS and TI. Therefore, OSI is considered as one of the values ​​of the global indicator in the assessment of acoustic bone.
To assess muscle strength, we used grip strength, which is thought to reflect whole-body muscle strength37,38. We follow the methodology of the “New Physical Fitness Test”39 of the Sports Bureau of the Ministry of Education, Culture, Sports, Science and Technology.
Smedley gripping dynamometer (TKK 5401; Takei Scientific Instruments Co., Ltd., Niigata, Japan). It is used to measure grip strength and adjust grip width so that the proximal interphalangeal joint of the ring finger is flexed 90°. When measuring, the position of the limb is standing with outstretched legs, the arrow of the hand gauge is kept facing outward, the shoulders are slightly shifted to the sides, not touching the body. Participants were then asked to grip the dynamometer with full force as they exhaled. During the measurement, the participants were asked to keep the handle of the dynamometer still while maintaining the basic posture. Each hand is measured twice, and the left and right hands are measured alternately to get the best value.
In the early morning on an empty stomach, blood was collected from third grade junior high school children, and the blood test was submitted to LSI Medience Co., Ltd. The company also measured bone formation (BAP) and bone mass using the CLEIA (enzymatic immunochemiluminescent assay) method. for the resorption marker (NTX).
Measures obtained in the fifth grade of elementary school and the third grade of junior high school were compared using paired t-tests.
To explore potential confounding factors, correlations between OSI for each class and height, body fat percentage, muscle percentage, and grip strength were validated using partial correlation coefficients. For third grade high school students, correlations between OSI, BAP, and NTX were confirmed using partial correlation coefficients.
To investigate the effect of changes in physique and strength from grade five of elementary school to grade three of junior high school on OSI, changes in body fat percentage, muscle mass, and grip strength associated with changes in OSI were examined. Use multiple regression analysis. In this analysis, the change in OSI was used as the target variable and the change in each element was used as the explanatory variable.
Logistic regression analysis was used to calculate odds ratios with 95% confidence intervals to estimate the relationship between fitness parameters in the fifth grade of elementary school and bone metabolism (OSI, BAP and NTX) in the third grade of high school.
Height, body fat percentage, muscle percentage, and grip strength were used as indicators of fitness/fitness for elementary fifth grade students, each of which was used to categorize students into low, medium, and high tertile groups.
SPSS 16.0J software (SPSS Inc., Chicago, IL, USA) was used for statistical analysis and p values ​​<0.05 were considered statistically significant.
The purpose of the study, the right to withdraw from the study at any time, and data management practices (including data privacy and data anonymization) were explained in detail to all participants, and written consent was obtained from the participants themselves or from their parents. / guardians.
The Iwaki Health Promotion Project Primary and Secondary School Health Study was approved by the Hirosaki University Graduate School of Medicine Institutional Review Board (approval number 2009-048, 2010-084, 2011-111, 2013-339, 2014-060 and 2015). -075).
This study was registered with the University Hospitals Medical Information Network (UMIN-CTR, https://www.umin.ac.jp; exam name: Iwaki Health Promotion Project medical exam; and UMIN exam ID: UMIN000040459).
In boys, all indicators increased significantly, except for % fat, and in girls, all indicators increased significantly. In the third year of junior high school, the values ​​of the bone metabolism index in boys were also significantly higher than in girls, which indicated that the bone metabolism in boys during this period was more active than in girls.
For fifth grade girls, a positive correlation was found between body size/grip strength and OSI. However, this trend was not observed in boys.
In third grade boys, all body size/grip strength factors were positively correlated with OSI and negatively correlated with NTX and /BAP. In contrast, this trend was less pronounced in girls.
There were significant trends in the odds for higher OSI in third and fifth grade students in the peak height, fat percentage, muscle percentage, and grip strength groups.
In addition, higher height, body fat percentage, muscle percentage, and grip strength in fifth grade men and women tended to significantly lower the odds ratio for BAP and NTX scores in ninth grade.
Re-formation and resorption of bone occurs throughout life. These bone metabolic activities are regulated by various hormones40,41,42,43,44,45,46 and cytokines. There are two peaks in bone growth: primary growth before age 5 and secondary growth during adolescence. In the secondary phase of growth, the growth of the long axis of the bone is completed, the epiphyseal line closes, the trabecular bone becomes dense, and BMD improves. The participants in this study were in a period of development of secondary sexual characteristics, when the secretion of sex hormones was active and factors affecting bone metabolism were intertwined. Rauchenzauner et al. [47] reported that bone metabolism in adolescence is highly variable with age and gender, and that both BAP and tartrate-resistant phosphatase, a marker of bone resorption, decrease after 15 years of age. However, no studies have been conducted to investigate these factors in Japanese adolescents. There are also very limited reports on trends in DXA-related markers and factors of bone metabolism in Japanese adolescents. One reason for this is the reluctance of parents and caregivers to allow invasive tests on their children, such as blood collection and radiation, without diagnosis or treatment.
For fifth grade girls, a positive correlation was found between body size/grip strength and OSI. However, this trend was not observed in boys. This suggests that the development of body size during early puberty influences OSI in girls.
All body shape/grip strength factors were positively associated with OSI in third grade boys. In contrast, this trend was less pronounced in girls, where only changes in muscle percentage and grip strength were positively associated with OSI. Changes in body muscle proportions were positively correlated with changes in OSI between sexes. These results suggest that in boys, an increase in body size/muscle strength from grades 5 to 3 affects OSI.
Height, body-muscle ratio, and grip strength in the fifth grade of elementary school were significantly positively correlated with the OSI index and significantly negatively correlated with measures of bone metabolism in the third grade of high school. These data suggest that the development of body size (height and body-to-body ratio) and grip strength in early adolescence affects OSI and bone metabolism.
The second age of peak growth rate (PHVA) in Japanese was observed at 13 years for boys and 11 years for girls, with faster growth in boys49. At the age of 17 years in boys and 15 years in girls, the epiphyseal line begins to close, and the BMD increases towards the BMD. Given this background and the results of this study, we hypothesize that increasing height, muscle mass, and muscle strength in girls up to grade five is important for increasing BMD.
Previous studies of growing children and adolescents have shown that markers of bone resorption and bone formation eventually increase50. This may reflect active bone metabolism.
The relationship between bone metabolism and BMD has been the subject of many studies in adults51,52. Although some reports53, 54, 55, 56 show slightly different trends in men, a review of previous findings can be summarized as follows: “Markers of bone metabolism increase during growth, then decrease and remain unchanged until the age of 40, old age.” .
In Japan, BAP reference values ​​are 3.7–20.9 µg/L for healthy men and 2.9–14.5 µg/L for healthy premenopausal women. Reference values ​​for NTX are 9.5-17.7 nmol BCE/L for healthy men and 7.5-16.5 nmol BCE/L for healthy premenopausal women. Compared to these reference values ​​in our study, both indicators improved in third-graders of lower secondary school, which was more pronounced in boys. This indicates the activity of bone metabolism in third-graders, especially boys. The reason for the gender difference may be that the boys of the 3rd grade are still in the growth phase and the epiphyseal line has not yet closed, while in girls in this period the epiphyseal line is closer to closing. That is, boys in the third grade are still developing and have active skeletal growth, while girls are at the end of the skeletal growth period and reaching the stage of skeletal maturity. Trends in bone metabolism markers obtained in this study corresponded to the age of maximum growth rate in the Japanese population.
In addition, the results of this study showed that fifth-grade elementary school students with a strong physique and physical strength had a younger age at the peak of bone metabolism.
However, a limitation of this study is that the effect of menstruation was not taken into account. Because bone metabolism is influenced by sex hormones, future studies need to investigate the effect of menstruation.