The mean age of the study population was 52 years (range, 40 to 67) in 1986. The median physical activity level in 1986 was 7.8 MET hours per week. In accordance with the changes in the questionnaire described above, the median activity level rose in 1988 to 9.0 MET hours per week, in 1992 to 12.2 MET hours per week, and in 1994 to 12.7 MET hours per week. In 1996, the median declined slightly to 11.0 MET hours per week. Physical activity change slopes ranged from −6.3 to 13.9 with a mean of 0.003. The mean BMI in 1986 was 24.5 kg/m2. While 20 percent of participants were current smokers in 1986, 45 percent had never smoked.
Women whose activity decreased had the highest median level of physical activity in 1986 (). Women whose activity increased had the highest median levels of physical activity in 1996. Mean BMI did not vary substantially across quartiles of physical activity change. With the possible exception of hypertension, the prevalence of the four chronic conditions did not markedly vary across quartiles of physical activity change.
Characteristics of women by quartile of long-term physical activity change from 1986 to 1996
In general, women reported high scores on all dimensions of health-related quality of life. All scales had median scores of 70 or above. Social functioning, role limitations due to physical problems and role limitations due to social problems all had a median score of 100. The mean change in SF-36 scores from 1996 to 2000 was generally not large, but there was a wide range indicating that women both increased and decreased scores during this time ().
Mean change and standard deviation in SF-36 score from 1996 to 2000
Compared to women who did not change their physical activity, women who had some or substantial increases in physical activity from 1986 to 1996 had higher 1996 SF-36 scores.() Women whose activity increased had an eight-unit higher score in physical functioning (8.19, 95% CI 7.76, 8.62) and role limitations due to physical problems (8.23, 95% CI 7.49, 8.97) scores than women whose activity was stable. The smallest improvement was on the mental health scale where increasing physical activity was associated with a 2.23 (95% CI 1.94, 2.52) unit higher score compared to women with a stable physical activity level.
Coefficient (95% confidence interval) for quality of life measures associated with quartiles of change in physical activity, 1986 to 1996, Nurses Health Study
Improvement in physical activity profile was also associated with a subsequent increase in SF-36 scores. Women who increased their activity saw over a two unit (2.64, 95% CI 1.90, 3.38) greater improvement in role limitations due to physical problems from 1996 to 2000 as compared to women with stable physical activity from 1986 to 1996. Long-term physical activity patterns had the smallest impact on mental health, where the increases in SF-36 score change were small for all groups of physical activity change, including women who increased their physical activity (0.35, 95% CI 0.12, 0.58).
Further adjustment for smoking, BMI and chronic conditions slightly attenuated change in SF-36 scores. The greatest attenuations occurred for role limitations due to physical problems, where, among women who increased their physical activity, the adjusted score fell from 2.64 (95% CI 1.90, 3.38) to 1.81 (95% CI 1.09, 2.53), and bodily pain, which decreased from 1.20 (95% CI 0.81, 1.59) to 0.75 (95% CI 0.38, 1.12).
When evaluating relations within strata of baseline BMI, the findings remained quite consistent across the three categories of BMI less than 35 (). However, in Class II obese women, increasing physical activity was associated with larger improvements in both social functioning and role limitations due to emotional problems, while having little impact on vitality as compared to women whose physical activity was stable. In analyses stratified by baseline smoking status (), the association appeared to differ only for role limitations due to emotional problems and vitality.
Coefficients (95% confidence interval) by baseline BMI for change in quality-of-life measures, 1996–2000, associated with a quartile of change in physical activity, 1986 to 1996, Nurses Health Study a
Coefficients (95% confidence interval) by baseline smoking status for change in quality-of-life measures, 1996–2000, associated quartile of change in physical activity, 1986 to 1996, Nurses Health Study a
Women who developed chronic conditions (arthritis, hypertension, diabetes, hypercholesterolemia) between 1986 and 2000 had the greatest improvements for all domains except bodily pain and role limitations due to physical problems when comparing women who increased their activity to women whose activity was stable (). Women who developed chronic conditions before 1986 had slightly higher coefficients, comparing women who increased activity to those with stable activity, than women who remained free of chronic conditions through 2000, with the exception of physical functioning (1.57 vs. 1.56) and social functioning (0.47 vs. 0.43). In analyses by quartile of baseline physical activity there was no substantial variation across strata with the possible exception of role limitations due to physical problems (data not shown).
Table 5 Coefficients (95% confidence interval) by presence of chronic conditions (arthritis, hypertension, diabetes, hypercholesterolemia) for change in quality-of-life measures, 1996–2000, associated with quartile of change in physical activity, 1986 (more ...)