Interaction effect of nocturnal sleep duration and physical activity on bone strength: a cross-sectional study of Chinese preschoolers

Aim Optimizing bone strength and bone density in childhood can greatly reduce the occurrence of osteoporosis in adulthood. We aimed to investigate the influence and interaction of sleep duration and physical activity (PA) with respect to bone strength among 1221 Chinese preschoolers.Subject and methods Information on sleep and PA was obtained from the guardians of preschoolers during the annual physical examinations at seven kindergartens in 2019. Bone strength was defined using the percentage of the ultrasonic speed for Asian children of the same age and sex. Generalized linear regression models were used to compare bone strength in participants with different sleep durations and types and different levels of PA.Results The results showed a significant correlation between sleep duration and bone strength, especially average nocturnal sleep duration (beta = 2.37; 95% CI: 0.59, 4.15). A stable link between PA and bone strength was also observed, mainly reflected in the average PA time (beta = 1.29; 95% CI: 0.35, 2.22) and walking time (beta = 0.20; 95% CI: 0.00, 0.39), but no association was found in moderate to vigorous PA (P > 0.05). In addition, we found a very strong interaction between average nocturnal sleep duration and PA for bone strength (beta = 0.14; 95% CI: 0.05, 0.23).Conclusion Adequate sleep duration combined with moderate PA is associated with greater bone strength. This association needs to be confirmed in further prospective studies.