Smoking and overweight as predictors of hospitalization for back disorders

Study Design. A prospective cohort study. Objective. To study the relationship of smoking and overweight with severe back disorders leading to hospitalization. Summary of Background Data. Many epidemiological studies have shown an association between smoking or overweight and back pain, but the results are still equivocal. Longitudinal studies are few. Methods. A cohort of metal industry employees (n = 902) was studied for lifestyle, work history, and health in 1973 by questionnaire and interview. The weight of the subjects was measured and body mass index (kg/m(2)) was calculated. Based on intensity and duration, smoking was categorized as: never smoked (reference), stopped smoking, smoked less than or equal to9 or >9 pack-years. Information on hospital admissions from 1973 to 2000 from the Finnish Hospital Discharge Register was linked to the data. Seventy-five individuals had been admitted to hospital because of back disorders. Intervertebral disc disorders and other common back disorders were analyzed separately. Cox proportional hazards regression was used to estimate the time between the assessment of potential risk factors and the first hospitalization for a back disorder. Results. The rate ratio of heavy smokers (>9 pack-years) for hospitalization because of intervertebral disc disorders was 3.4 (95% confidence interval 1.3-9.0) as compared with never-smokers, allowing for other risk factors. Accordingly, the rate ratio of body mass index >27.5 kg/m(2) was 2.7 (1.1-6.45) as compared with people with normal weight. The results retained when patients with chronic back disease at baseline were excluded from the analyses. Other back-related diagnoses of hospitalization were not consistently associated with smoking or overweight. Conclusion. Heavy smoking and overweight predicted hospitalization for intervertebral disc disorders.