Effect of occupational physical activities on vertebral dimensions in midlife in the Northern Finland Birth Cohort 1966.

OBJECTIVES: The vertebral cross-sectional area (CSA) is a major determinant of vertebral strength. Since leisure-time physical activity (LTPA) is known to affect vertebral CSA, we hypothesised that engagement in physical activity at work might have similar effects on vertebral size. We aimed to examine the association between various adulthood occupational physical activities (OPA) and vertebral CSA, and to evaluate the association between OPA intensity and vertebral CSA.

METHODS: We used the prospective population-based Northern Finland Birth Cohort 1966. Our sample consisted of 712 participants with a mean age of 46.8 years. We assessed their engagement in various individual physical work activities at the ages of 31 and 46, and created overall OPA categories (high, moderate and low intensity), which we used in the analyses to study their association with vertebral CSA in middle age. Linear regression was used as the statistical method with adjustments for LTPA, vertebral height, body mass index and smoking.

RESULTS: A statistically significant association was found between occupational sitting and smaller vertebral CSA in men, but only at the age of 31 (49.2 mm2 smaller among those who sit often vs rarely (95% CI -96.0 to -2.4)). No significant differences were detected between OPA categories and vertebral CSA (p>0.05). Thus, we found no consistent association between OPA and vertebral size among either sex.

CONCLUSIONS: OPA seems to have very little effect on vertebral size. Our results suggest that the effect of LTPA on vertebral size is different to that of OPA.