Hand grip strength trajectories and the risk of low bone mineral density in 6-7-year-old children: a prospective study

Hand grip strength (HGS) is significantly correlated with bone mineral density (BMD), but has been assessed at a single time point in the cross-sectional study. The relationship between long-term patterns of HGS and BMD has neglected and not been proven. Therefore, this study aimed to explore the long-term HGS trajectories in 6-7 years old children and the risk of low BMD. This study included 1122 individuals with healthy BMD from Hebei Children and Adolescents aged 6-7 years Cohort Study in 2018 (baseline). HGS was measured 3 times repeatedly in 2018, 2020, and 2022. A cohort-based trajectory model was used to identify 4-year HGS developmental trajectories in the total participants, while HGS developmental trajectories were identified separately in subgroup analyses for sex, body mass index (BMI), and height. Cox proportional hazards models were used to test the association between HGS trajectories and low BMD. Three trajectories of HGS in the 1122 participants from 2018 to 2022 were identified and labeled as low-rate growth (blue-group1) (530, 47.2%), moderately-rate growth (red-group2) (518, 46.2%), and high-rate growth (green-group3) (74, 6.6%) respectively. Only 102 cases of low BMD were identified, the risk of low BMD was 9.1%. Participants in the low-rate growth group had a higher incidence of low BMD compared with the high-rate growth group [12.8% vs 2.7%, hazard ratio (HR): 5.74; 95% confidence interval (CI): 1.31, 25.15; P = 0.02]. Besides, the risk of low BMD decreased with the HGS changing trajectory increased in those two models (P-trend < 0.05). And the same dose-response relationship was demonstrated in subgroup analyses of sex (boys, girls); however, in subgroup analyses for body mass index (normal, overweight/obese) and height (<= median, > median), this relationship was only observed in those with normal BMI and height > P-50. Conclusion: The HGS changing trajectories were associated with the risk of new-onset low BMD, and low BMD risk decreased with the HGS changing trajectory increase. Future studies with larger sample sizes are needed to validate the relationship between HGS and BMD. Trial registration: Clinicaltrials.gov Identifier: ChiCTR2400083223; date registered: April 18, 2024. Registered under the name: "A bidirectional cohort study on the growth and development of children and adolescents in Hebei Province." What is Known: center dot Cross-sectional study finds significant correlation between handgrip strength (HGS) and bone mineral density (BMD). center dot The relationship between long-term patterns of HGS and BMD has neglected and not been proven. What is New: center dot Utilizing a group-based trajectory model to identify different patterns of HGS trajectories. center dot Low-rate growth HGS trajectory patterns are associated with a high risk of low BMD.