Cigarette smoking, body mass and other risk factors for fractures of the hip in women.

Determinants of hip fractures were assessed using data from a network of hospital-based case-control studies from northern Italy. For the present analysis, cases were 209 women with fractures of the hip/proximal femur (aged 29 to 74, median age 62) admitted to a network of teaching and general hospitals in the greater Milan area; controls were 1449 women, aged 25 to 74 (median age 55), admitted for non-traumatic, acute conditions to the same network of hospitals. There was a strong direct association with smoking, the relative risk (RR) being significantly and similarly elevated both in ex- and in current smokers (RR 1.7 and 1.5 respectively) which rose to 2.4 for 25 or over cigarettes per day. The risk was associated with duration of smoking and apparently greater in post-menopausal women. Two factors showed significant inverse associations with hip fractures: relative weight, with relative risks of 0.5, 0.4 and 0.3 in subsequent categories of body mass index as compared with thinner ones, and the use of oestrogen replacement treatment (multivariate RR = 0.4, 95% confidence interval (CI): 0.2-1.1). No association was observed with education or social class, selected indicator foods or alcohol consumption (RR for the highest consumption level = 1.0). The effects of smoking and body mass index appeared independent: compared with never smoking heavier women, the RR for smoking thin women was 4.6. Thus, this case-control study of hip fractures in a predominantly post-menopausal population of Italian women showed a strong association with smoking and appreciable protection from heavier body mass index and the use of oestrogen replacement treatment.