Income, educational level and body height

Because physical activity may affect hormonal concentrations and energy balance, we decided to investigate whether everyday exercise is related to the risk of breast cancer. During 1974 to 1978 and 1977 to 1983, a total of 25,624 women, 20 to 54 years of age at entry, enrolled in health surveys and answered questionnaires about leisure-time and work activity. During a median follow-up of 13.7 years, we identified 351 cases of invasive breast cancer among the 25,624 women in the cohort. Greater leisure-time activity was associated with a reduced risk of breast cancer, after adjustments for age, body-mass index (the weight in kilograms divided by the square of the height in meters), height, parity, and county of residence (relative risk, 0.63; 95 percent confidence interval, 0.42 to 0.95), among women who exercised regularly, as compared with sedentary women (P for trend=0.04). In regularly exercising women, the reduction in risk was greater in premenopausal women than in postmenopausal women, and greater in younger women ( or =45 years) (relative risk, 0.38; 95 percent confidence interval, 0.19 to 0.79). In stratified analyses the risk of breast cancer was lowest in lean women (body-mass index, <22.8) who exercised at least four hours per week (relative risk, 0.28; 95 percent confidence interval, 0.11 to 0.70). The risk was also reduced with higher levels of activity at work, and again there was a more pronounced effect among premenopausal than postmenopausal women. Physical activity during leisure time and at work is associated with a reduced risk of breast cancer.

Data from a prospective study were used to investigate risk factors for hip fracture among a representative population of middle-aged adults. During the years 1974-1978, all women (n = 25,298) and men (n = 27,015) aged 35-49 years in three Norwegian counties were invited to attend a cardiovascular screening (attendance rate = 91.5%). This cohort was followed throughout 1990 with respect to hip fracture, for a total of 572,006 person-years. A total of 281 new fractures were identified, of which 71 were excluded from the analysis due to high-energy trauma or fracture in metastatic bone. Age-adjusted relative risks (RR) and 95% confidence intervals (CI) for hip fracture increased with body height in women (RR = 3.62, 95% CI 1.46-8.97, > or = 1.70 m vs. or = 1.85 m vs. or = 15 cigarettes per day. In multivariate analysis, all these risks remained elevated. This study suggests that, as in older populations, known risk factors for low bone mass are related to hip fracture among middle-aged adults. In addition, body height seems to have an independent influence on hip fracture incidence in this age group.

The height and weight of 570,000 Norwegian women, aged 30-69 years, were measured and the subjects were then followed up for 6-18 years with regard to breast cancer morbidity and mortality. They were arranged in 5-year age-groups. In all age-groups the tallest women were found to have the highest risk for both morbidity and mortality. Overweight was a risk factor for breast cancer mortality in all age-groups, but it was a risk factor only in the post-menopausal age-groups in the case of morbidity. It appeared to protect against breast cancer in the pre-menopausal age-group. Stages I and II-IV follow-up endpoints show negative and positive associations, respectively, with overweight. It is not likely that this can be fully explained by earlier detection of cancer among slim women.