The present study aimed at exploring the relations between body mass index (BMI, (weight in kilograms)/(height in meters) 2 ) and stature and cancer of the small intestine (1162 cases) in a large Norwegian cohort (of two million) with measured height and weight. Elevated BMI in males and increasing height in both sexes were associated with a moderately increased risk of cancer of the small intestine. Overweight or obesity has been linked to an increased risk of several site-specific cancers, including colorectal cancers (Engeland et al, 2005). A large cohort study of male US veterans found a significant excess risk of small intestine cancer, especially of the duodenum, among obese white veterans (Samanic et al, 2004). Also, a recent cohort study of obese individuals in Sweden reported a significantly elevated risk of cancer of the small intestine, but only among men (Wolk et al, 2001).The aim of the present study was to explore the associations between body mass index (BMI) and height and the risk of cancers of the small intestine in a very large Norwegian cohort of both men and women with a long follow-up.
STUDY POPULATIONThe study population has been described in detail elsewhere, (Engeland et al, 2004).Briefly in a series of health surveys during 1963 -2001, height and weight were measured in a standardised way by a trained staff in 2 001 727 persons (963 709 men and 1 038 018 women) aged 20 -74 years. Deaths, emigrations and cases of cancer of the small intestine (International Classification of Diseases, seventh revision (ICD-7): 152) in this cohort were identified by linkage to the Death Registry at Statistics Norway (Statistics Norway, 2005) and to the Cancer Registry of Norway (The Cancer Registry of Norway, 2005). Both these registries are population based and are covering the entire Norwegian population. A unique 11-digit identification number assigned to all individuals living in Norway after 1960 simplified the linkages.In the present study, only histologically verified cancers of the small intestine were included. Persons with a diagnosis of cancer of the small intestine, prior to the height and weight measurements, were excluded. Consequently, 32 persons were excluded in the analyses. In the analyses, the persons in the cohort were followed up from the date of measurement until the date of cancer diagnosis, emigration, age 100 years, death or until 31 December 2003. Altogether, 2 001 695 persons were eligible for the study. A small number of these (39 men and 32 women) were lost to follow-up.
STATISTICAL METHODSCox's proportional-hazards regression models (Cox and Oakes, 1984), with time since measurement as the time variable, were fitted to obtain relative risk (RR) estimates of cancer. In the analyses, categorised variables for age at measurement, year of birth, BMI ((weight in kilograms)/(height in meters) 2 ) and height were included. BMI was categorised using the WHO categorisation (World Health Organization Consultation on Obesity, 1998): BMI o18.5 (underweight), 18.5 -24.9 (normal), 25.0 -2...