Total physical activity in middle-aged and elderly women from a population-based cohort

Abstract

Regularly performed physical activity (PA) is associated with a reduced risk of coronary heart disease, stroke, type 2 diabetes, some forms of cancer, osteoporosis, and all-cause mortality. Due to its role in health promotion and disease prevention, PA is a particularly important health behavior to be investigated. The first aim of this thesis was to investigate temporal trends and correlates of total PA using data from the Swedish Mammography Cohort (SMC). The second aim was to evaluate the reproducibility and validity of self-reported PA and to make a profile of PA behaviors using accelerometer data from a subset of the SMC.

The SMC is a population-based prospective cohort established between 1987 and 1990 in Uppsala and Västmanland Counties. In our analyses among 38,988 women between the ages of 48 and 83 years, we observed a decreasing trend of total PA by calendar time between the 1930s and the 1990s. Total activity level decreased in all age groups (15, 30, and 50 years of age) by an average of 3 MET-hours/day corresponding to about 45 minutes of brisk walking. The likelihood of engaging in higher total daily PA levels linearly decreased with age (for 5-year increase: odds ratio (OR) = 0.87; 95% confidence interval (Cl): 0.85-0.89) and body mass index (for 5-unit, kg/m2, increase: OR= 0.81; 95% Cl: 0.79-0.84). Total PA levels were inversely associated with smoking (OR= 0.83; 95% Cl: 0.79-0,88), drinking (OR= 0.88 95% Cl: 0.82-0.94), educational level (university vs. primary: OR=0.54, 95% Cl: 0.51-0.58), and childhood environment (city vs. countryside: OR= O.62, 95% Cl: 0.59-0.65).

Reproducibility, as measured among 303 women by intraclass correlation (ICC) for total current PA, was 0.69. For historical PA, the reliabilities for total activity were from 0.75 for age 50 to 0.81 for age 30 years, being substantial for occupational activities (ICC=0.73-0.75), and fair to moderate for inactivity (ICC=0.31-0.60). Validity, as measured among 116 women by de-attenuated concordance correlations comparing total daily activity estimated by the questionnaire with the accelerometers and the records were 0.72 and 0.67, respectively. According to the PA recommendation to accumulate at least 30 minutes per day (in either 1 continuous bout or several shorter bouts lasting 8-10 minutes) of moderate-to-vigorous activity 5 days per week or more, we found that among 133 women the proportion who met this recommendation was 31% which decreased to 18% among obese women.

In conclusion, our findings from a large population-based prospective cohort of middle-aged and elderly women show that total PA has been decreasing by calendar time during the last 60 years of the 20th century. The likelihood of engaging in higher total daily PA levels decreased with age, body mass index, educational level, smoking, drinking, and growing up in urban places. Our short self-administered PA questionnaire was reasonably reproducible and valid. The fact that only a third of the women were not meeting the PA recommendation suggests that counselling messages may need to Place more emphasis on the correct number of days per week and in which way moderate activity should be obtained to achieve health benefits.