Assessing the association between a sedentary lifestyle and prevalence of primary osteoporosis: a community-based cross-sectional study among Chinese population

Strengths and limitations of this study

  • The survey was conducted in the community, and the participants were more in line with the characteristics of the natural population aged 40 and above.

  • Multiple regression models were established to examine the association between the prevalence of POP and study variable, with potential confounding variables systematically incorporated in a stepwise manner, enhancing the rigour of the analysis.

  • Screening did not fully represent diagnosis, although the screening diagnostic value of the calcaneus diagnostic instrument was calibrated to improve its screening accuracy.

  • Despite the collection of a substantial number of control variables for primary osteoporosis (POP), there are still potential confounding variables that may not be included in the control variables.

  • It is difficult to identify the causal relationship between a sedentary lifestyle and the prevalence of POP due to the cross-sectional study.

Introduction

Osteoporosis (OP) is a chronic, systemic bone disease characterised by bone loss, low bone mass and changes in bone microstructure, leading to decreased bone strength, increased bone fragility and a higher risk of fracture.1 OP is a global public health problem. An estimated 1.37 billion women and 21 million men worldwide are at high risk of osteoporotic fracture (OF), with about 9 million cases occurring each year.2 3 In China, an estimated 83.9 million people suffer from OP, which is likely to rise to around 212 million by 2055.4 As the population ages, OP has become a significant medical and socioeconomic burden. With the increasing social burden of OP and OF, OP prevention has become an important public health goal.5 6 It is now understood that POP is the main type of OP, and SOP is mainly a metabolic bone disease induced by specific diseases or long-term use of hormones and other drugs.7 Considering the unique pathogenesis of SOP, this study focused primarily on POP. The biological mechanism of POP is complicated and not fully understood. It may be related to ageing, heredity, endocrine disorders, environmental factors and unhealthy living behaviours.8 9

Sedentary behaviour, a widespread unhealthy lifestyle, has been linked to numerous chronic diseases, including cardiovascular disease, diabetes, cancer, anxiety, depression and obesity.10–14 Sedentary behaviour contributes to insulin resistance, lower cardiorespiratory fitness and loss of muscle mass. It is also associated with higher levels of body fat and visceral fat stores, elevated lipid levels and inflammation.15 Previous studies have also found that a sedentary lifestyle may be linked to reduced bone mass.16 Alterations in the balance of bone resorption and deposition play a crucial role in mediating the relationship between sedentary behaviour and osteopenia.17 However, there remains a dearth of population-based epidemiological evidence regarding the correlation between sedentary behaviour and POP risk.

Thus, we conducted POP screening in the community and collected the related factors of POP. Cross-sectional data analysis was performed to reveal the research question of whether a sedentary lifestyle is associated with POP prevalence in Chinese population. This study aims to provide valuable insights for the development of future public health intervention strategies for POP.

Methods

Study design

This research was a cross-sectional survey conducted within Chinese communities to examine the potential factors associated with the prevalence of POP. The study involved four main steps. First, literature research and expert consultation were conducted to identify relevant study and control variables associated with POP risk. Second, the optimal threshold for POP screening using calcaneus ultrasound bone mineral density (BMD) testing was determined. We randomly selected individuals in research communities to undergo both calcaneus ultrasound BMD testing and dual-energy X-ray absorptiometry (DXA) POP diagnosis. Third, an on-site questionnaire survey was conducted, during which all participants underwent calcaneus ultrasound BMD testing. Fourth, the survey data was organised and analysed to present the research findings.

The field investigation period for this study was divided into two batches. The first batch is from June to October 2022. In the first phase of a questionnaire survey, participants were surveyed and recruited for the analysis of the optimal threshold for POP screening. The second batch is from August to October 2023. The participants in the second batch of the questionnaire survey were residents who were selected in the first batch but did not participate in the survey. The second phase of the questionnaire survey also included additional information collection on the control variables that needed to be added in the firstbatch.

Study population

The participants of this study were from communities in Hongguang street of Yaohai district, Sanlian street of Shushan district, Haitang street of Luyang district and Binhushiji street of Baohe district, Hefei city, Anhui province, China. Participants were primarily residents aged 40 and above who were undergoing routine community health examinations. All participants were identified by randomised sampling. Systematic sampling was conducted based on their health examination numbers. The health examination number of residents was coded by the address number and ID code. During the field investigation, investigators explained the study’s purpose and obtained oral consent before administering a questionnaire survey, as a portion of the community residents lacked reading proficiency.

Participants met the following inclusion criteria: 40 years of age or older and a regular lifestyle (stable dietary, sleep, exercise, smoking and drinking habits). Exclusion criteria aimed to minimise the influence of SOP and other diseases on bone health. These criteria included: (1) long-term use of hormone medications (glucocorticoids, hormones, thyroid hormones, insulin, etc), (2) endocrine and metabolic diseases (diabetes, hyperthyroidism, hypothyroidism, etc), (3) autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, gout, etc), (4) gastrointestinal diseases (chronic liver diseases, those with gastrointestinal resection) and (5) other chronic diseases (malignant tumours, chronic kidney disease, etc).

Data collection

The present study assessed sedentary behaviour by measuring the average daily sitting time, which was categorised into four levels: less than 2 hours, 2–4 hours, 4–6 hours and 6 hours or more. In this study, average daily sitting time referred to the cumulative average time spent sitting during waking hours, including work and daily activities. The control variables mainly include general information, dietary information and life behaviour information. The determination of the investigation content was based on a literature review and expert consultation. Trained investigators conducted the field investigation using a self-administered questionnaire. After obtaining informed consent from the participants, investigators recorded the relevant information of the participants according to face-to-face survey and community health electronic records.

A calcaneal ultrasound bone densitometer (BROSHARE Technology Company, China, model BX-BDI-500A) operating at a probe frequency of 500 kHz±10% was used for community POP screening. The measurement site was the calcaneus. DXA imaging bone densitometry (Lunar Prodigy pro, General Electric Company, USA) was used to diagnose POP. The measurement site was the lumbar spine (L1-L4), and a minimum t-value less than −2.5 was considered diagnostic of POP. Before the community investigation, participants were recruited, and the receiver operating characteristic curve (ROC) was drawn based on the results of POP DXA diagnosis and calcaneus ultrasound BMD testing. The optimal threshold for positive POP screening was determined according to the principle of the highest Youden Index. 164 individuals were randomly recruited from the study participants. The area under the curve of ROC was 0.94 (95% CI=0.90 to 0.98, p<0.001). When the t-value of the ultrasonic examination was −1.55, the Youden Index reached its maximum value (0.70), with a sensitivity of 85.2% and a specificity of 84.7%. Therefore, a t-value of −1.55 was set as the uniform threshold for positive calcaneal ultrasound POP screening in this study.

Patient and public involvement

No patient is involved.

Statistical analysis

Quantitative data were represented by the mean±SD if normally distributed, and by the median and IQR if not normally distributed. T-tests were used to compare normally distributed quantitative data means, while Mann-Whitney U tests were used for non-normally distributed data. χ2 tests were used to compare the frequencies, proportions and distributions of categorical data. Logistic regression was used to analyse the relationship between the prevalence of POP and study or control variables. ORs and 95% CIs were calculated using logistic regression analysis.

Results

Basic characteristics of research participants

A total of 1346 individuals meeting the inclusion and exclusion criteria were included in this study and underwent calcaneal ultrasound POP screening. Of these, 247 participants were identified as POP (+) based on the uniform threshold, while the remaining 1099 participants were classified as POP (−). The characteristics of the study variable (average daily sitting time) and 15 control variables were analysed between the POP (+) and POP (−) groups. The results, presented in table 1 and table 2, revealed statistically significant differences in 6 variables: gender, age, body mass index (BMI), occupation, fracture history and family history.

Table 1

Basic characteristics (part 1) of research objects

Table 2

Basic characteristics (part 2) of research objects

Association between the prevalence of POP and control variables

To analyse the relationship between POP and control variables, multiple regression models were built using POP screening results as the dependent variable. The analysis revealed that gender, age and BMI had a statistically significant correlation with POP across all models (crude, Model 1, Model 2, Model 3 and Model 4), as shown in table 3. Specifically, women had a higher prevalence of POP compared with men. Additionally, the prevalence of POP increased with age, while a higher BMI was associated with a lower prevalence of POP. Other control variables showed no significant correlation with POP prevalence in the final models.

Table 3

Association between the prevalence of POP and control variables in different models

Association between the prevalence of POP and average daily sitting time

The average daily sitting time showed a significant positive correlation with the prevalence of POP in all models (crude model, Model 1, Model 2, Model 3 and Model 4) (table 4, table 5). Specifically, the OR and 95% CI were: crude model (OR=2.02, 95% CI=1.74 to 2.36, p<0.001), Model 1 (OR=2.65, 95% CI=2.21 to 3.17, p<0.001), Model 2 (OR=2.63, 95% CI=2.19 to 3.15, p<0.001), Model 3 (OR=2.62, 95% CI=2.18 to 3.15, p<0.001) and Model 4 (OR=2.58, 95% CI=2.14 to 3.11, p<0.001). Compared with the <2 hours subgroup, individuals in the 2–4 hours subgroup (OR=14.42, 95% CI=5.19 to 40.05, p<0.001), the 4–6 hours subgroup (OR=27.20, 95% CI=9.71 to 76.22, p<0.001) and the ≥6 hours subgroup (OR=57.84, 95% CI=20.00 to 168.25, p<0.001) had a significantly higher OR of POP in Model 4. Additionally, the OR of POP increased significantly with increasing average daily sitting time (P for trend <0.001).

Table 4

Association between the prevalence of POP and average daily sitting time in different models based on gender, age and BMI subgroups

Table 5

Association between the prevalence of POP and average daily sitting time in different models

Based on the analysis of associations between the prevalence of POP and control variables, gender, age and BMI are independent risk factors for POP. We further explored the association between average daily sitting time and the prevalence of POP stratified by gender, age and BMI. Both male and female subgroups showed a significant correlation with the prevalence of POP in all models (crude model, Model 1, Model 2, Model 3 and Model 4) (table 4). All age subgroups (40–50, 50–60, 60–70, ≥70 years) showed a significant correlation with the prevalence of POP in Model 4 (table 4). All BMI subgroups (≥28 kg/m2, 24.0–28.0 kg/m2, 18.5–24.0 kg/m2) showed a significant correlation with the prevalence of POP in all models (crude model, Model 1, Model 2, Model 3 and Model 4). However, the BMI subgroup <18.5 kg/m2 did not show a significant correlation with the prevalence of POP in Models 3 and 4 (table 4).

Discussion

This study investigated the population characteristics and prevalence of POP among residents aged 40 and over in communities of Hefei, Anhui province, China. Based on the literature review and expert consultation, we identified average daily sitting time as the study variable and 15 POP potential risk factors as control variables. Notably, our results revealed a significant correlation between average daily sitting time and POP prevalence, suggesting that a sedentary lifestyle may be an independent risk factor for POP in the Chinese population.

While few prior studies have directly investigated the link between sedentary lifestyle and POP prevalence, some have shown an association between sedentariness and increased fracture risk. For instance, a study conducted in Valencia, Spain, found that sedentariness was a common risk factor for fractures in postmenopausal women.18 Similarly, a unique patient survey from the Own the Bone program registry suggested a 10% increase in the likelihood of recommending anti-OP treatment for sedentary individuals.19 A study focused on women over 50 showed that replacing sedentary time with light physical activity may reduce the risk of OP, fractures, mortality and medical costs.20 Another case–control study supported this notion, finding that sedentariness was associated with a higher risk of hip fracture in women compared with moderate and high levels of recreational physical activity.21 Previous research has also generally suggested that sedentariness, often linked to lower physical activity levels, may contribute to an increased risk of OP.22 Interestingly, after adjusting for exercise habits in this study, the results showed no correlation or interaction between sedentariness and exercise habits, implying that sedentary behaviour may be an independent risk factor for POP.

The pathogenesis of POP is complex and multifactorial, involving factors such as ageing, heredity, endocrine disorders, sedentary lifestyle and environmental factors.8 9 Bone homeostasis is maintained by a delicate balance between osteoclast-mediated bone resorption and osteoblast-driven bone formation. When resorption outpaces formation, bone balance is disrupted.23 Previous studies have shown that appropriate mechanical stimulation from physical activity promotes the differentiation of mesenchymal stem cells into osteoblasts. Sedentary individuals often lack this stimulation, which may lead to increased expression of peroxisome proliferation-activated receptor (PPAR)-γ and inhibited expression of the osteogenic transcription factor Runx2.24 25 While (PPAR)-γ can both inhibit Wnt signalling and promote osteogenesis, prolonged suspension of mechanical stimulation due to sedentariness might lead to catabolism of muscles, tendons, ligaments and rapid bone resorption.26–28 Other studies suggest that sedentariness may affect cellular metabolic processes, increase oxidative stress and contribute to an imbalance in bone homeostasis.29 30

This study found that gender, age and BMI were significantly correlated with the prevalence of POP among the control variables. Specifically, women had a higher prevalence of POP compared with men. This aligns with prior research demonstrating a higher prevalence of OP in postmenopausal women compared with men, with a female-to-male ratio of 2–3 times.31 Postmenopausal women (over 50 years old) have a fourfold increased prevalence of OP compared with men. Additionally, the prevalence of osteopenia in women over 50 is twice that of men in the same age group. A prospective cohort study in China found a higher incidence of hip fracture in adult women compared with men, and the rate of OP increased faster in women over 50 than in men.32 Stratification by age revealed a higher prevalence of POP within the older age group compared with the younger age group. Furthermore, a statistically significant positive trend (P for trend) was observed in the OR for POP across different models, indicating an association between increasing age and a rising likelihood of POP. This is consistent with previous studies.33 Our subgroup analysis showed a lower prevalence of POP in the higher BMI groups compared with the lower BMI groups, with a significant P for trend across models. Prior research suggests that low BMI is a potential risk factor for OP at various bone sites, although the mechanism remains unclear.34

This study acknowledges several limitations in examining the relationship between sedentary behaviour and POP. The control variables may not be comprehensive. For example, dietary intake data was collected but excluded from the analysis because dietary intake surveys were difficult to quantify in the community. Similarly, other factors like concurrent chronic diseases and functional ability were not included due to community survey limitations. The use of cross-sectional survey data introduces potential biases. For instance, the study population may include both new and existing POP cases, and participants may unintentionally exaggerate or under-report dietary and lifestyle behaviours. While calcaneal ultrasound was chosen due to its acceptability for community screening and its relatively high diagnostic accuracy, there may still be discrepancies between screening results and definitive diagnosis using DXA equipment, though the ROC curve was established to optimise the accuracy of calcaneal ultrasound screening.

In summary, a sedentary lifestyle may be an independent risk factor for POP in the Chinese population. Future longitudinal cohort studies are needed to confirm whether changes in sedentary behaviour can reduce POP risk. Additionally, gender, age and BMI were identified as important factors affecting POP prevalence. A thorough examination of these factors in future research may provide valuable insights for developing public health intervention strategies aimed at preventing and managing POP among this population.

Supplemental material

Data availability statement

No data are available.

Ethics statements

Patient consent for publication

Ethics approval

This study involves human participants and was approved by the Committee on Medical Ethics of The First Affiliated Hospital of Anhui Medical University, Reference number: Quick-PJ 2023-11-41. Participants gave informed consent to participate in the study before taking part.

Acknowledgments

We thank all the residents for participating in the survey.

This post was originally published on https://bmjopen.bmj.com