INTERACTION BETWEEN CURRENT SMOKING, LEANNESS, AND PHYSICAL INACTIVITY IN THE PREDICTION OF HIP FRACTURE

To study the association between smoking habits and the incidence of h ip fracture, adjusted for leanness and physical inactivity, a cohort s tudy with 3 years follow-up was conducted. Subjects were 34,856 adults aged 50 years or older who attended a health screening in Nord-Tronde lag County in Norway in 1984-1986 (91% of eligible subjects in 1986, n = 38,356). Of these, 421 suffered a hip fracture during the years 198 6-1989. Using Cox regression models, the relative risk (with 95% confi dence interval) of suffering a hip fracture for female smokers versus nonsmokers was 1.5 (1.0-2.4). These results refer to females when the female body mass index (BMI) was set at 25 kg/m(2) in the female model (the mean BMI for the smoking female population in this study). Among thinner females, however, smoking had a much stronger effect. For ins tance, if the female BMI was set at 20 kg/m(2), the relative risk was 3.0 (1.8-5.0). The relative risk of hip fracture for male smokers vers us nonsmokers was 1.8 (1.2-2.9) irrespective of BMI. Smoking is associ ated with incidence of hip fracture in both sexes and also after adjus ting for body mass index and physical inactivity (the effect of physic al inactivity was adjusted for self-reported ill health because ill he alth was included in the model). For lean females, the association wit h current smoking was large, as large as if they added 10 years to the ir age.