Prevalence of osteoporosis and fractures in a migrant population from southern to northern Italy: a cross-sectional, comparative study

The purpose of this study was to assess whether a migrant population from southern regions of Italy showed differences in osteoporosis (OP) and fracture prevalence in comparison to a population born and living in Milan, a city in northern Italy. The study group consisted of 1764 postmenopausal women born in southern Italy who migrated after age 20 to Milan, where they had lived for at least 15 years. This group was compared with a sample of 4018 postmenopausal women born, raised and living in Milan. Bone mineral density (BMD) was measured at lumbar spine by dual-energy X-ray absorptiometry. Univariate analysis showed a significantly higher BMI, a greater parity, a lower postmenopausal estrogen (HRT) usage and a lower calcium intake in the Southern group (SG). Densitometric values showed a mean lumbar BMD significantly lower in SG (P<0.001), resulting in a greater prevalence of OP (30.5% versus 24.9%; P<0.001). Consistent with this result, the number of women reporting low energy fractures after menopause was higher in SG (4.8% versus 3.6%; P=0.01). Multiple logistic regression analyses showed that OP was predicted by well-recognized variables, such as age, age at menopause, BMI, HRT, calcium intake together to belonging to SG, which independently increased the risk for OP by 42%. Age, age at menopause, BMI and belonging to SG significantly influenced the fracture risk, but the last variable was no longer associated with an increased fracture risk when BMD was entered in the model. Despite the results of previous epidemiological studies and protective anthropometric measures, a higher OP and fracture prevalence was found in the migrant group from southern Italy to Milan in comparison with the native sample. These differences are not solely explained by lifestyle variables. Our data suggest that changing environmental exposures can influence bone mass and fracture risk.