Research Article
Sedentary Behavior and Mortality in Older Women: The Women’s Health Initiative

https://doi.org/10.1016/j.amepre.2013.10.021Get rights and content

Background

Although epidemiologic studies have shown associations between sedentary behavior and mortality, few have focused on older women with adequate minority representation and few have controlled for both physical activity and functional status.

Purpose

The objective of this study was to determine the relationship between sedentary time and total; cardiovascular disease (CVD); coronary heart disease (CHD); and cancer mortality in a prospective, multiethnic cohort of postmenopausal women.

Methods

The study population included 92,234 women aged 50–79 years at baseline (1993–1998) who participated in the Women’s Health Initiative Observational Study through September 2010. Self-reported sedentary time was assessed by questionnaire and examined in 4 categories (≤4, >4–8, ≥8–11, >11 hours). Mortality risks were examined using Cox proportional hazard models adjusting for confounders. Models were also stratified by age, race/ethnicity, body mass index, physical activity, physical function, and chronic disease to examine possible effect modification. Analyses were conducted in 2012–2013.

Results

The mean follow-up period was 12 years. Compared with women who reported the least sedentary time, women reporting the highest sedentary time had increased risk of all-cause mortality in the multivariate model (HR=1.12, 95% CI=1.05, 1.21). Results comparing the highest versus lowest categories for CVD, CHD, and cancer mortality were as follows: HR=1.13, 95% CI=0.99, 1.29; HR=1.27, 95% CI=1.04, 1.55; and HR=1.21, 95% CI=1.07, 1.37, respectively. For all mortality outcomes, there were significant linear tests for trend.

Conclusions

There was a linear relationship between greater amounts of sedentary time and mortality risk after controlling for multiple potential confounders.

Introduction

There is strong evidence that 10-minute or more bouts of moderate to vigorous physical activity (MVPA) provide substantial health benefits, with higher doses producing greater benefits.1 There is also increasing evidence that less time spent in sedentary activities provides health benefits. Epidemiologic studies suggest that less sedentary time may protect against premature death, independent of MVPA.2, 3, 4, 5, 6, 7 Other studies have reported that more sitting time was associated with increased risk for coronary heart disease (CHD)8; cardiovascular disease (CVD)9; and adverse metabolic effects such as obesity and insulin resistance.10, 11, 12, 13, 14, 15 In addition, it was estimated that life expectancy in the U.S. would increase by 2 years if people reduced sitting time to fewer than 3 hours/day.16

There appear to be plausible physiologic mechanisms by which sedentary time affects health. One possible explanation is that more sedentary time decreases metabolic activity of muscle and diminishes energy utilization, leading to insulin resistance and metabolic derangements. It has been demonstrated in animal models that lipoprotein lipase is deactivated in the muscle tissue during prolonged physical inactivity.10 Another study showed that prolonged sitting reduced blood clearance of glucose and reduced insulin secretion.17

Analyses of NHANES accelerometer data show that the most sedentary age group is adults aged ≥60 years, with adults aged 60–69 years engaging in 8.4 hours/day of sedentary behaviors and adults aged 70–85 years engaging in 9.3 hours/day.18 However, long-term data on associations of sedentary time and mortality focusing specifically on women aged ≥50 years are limited; in fact, only one prior study of this age group has included a follow-up period of 10 years or longer.6

The goal of the present study was to determine the association between sedentary time and mortality—all-cause mortality and mortality due to CVD, CHD, and cancer. Given the large and diverse sample of this study, possible differences by age, race/ethnicity, BMI, physical activity, physical function, and multiple morbidity were also examined, as these variables are related to mortality and may also influence sedentary time.

Section snippets

Study Population

The cohort for this study was participants in the Women’s Health Initiative (WHI) Observational Study (OS) and Extension Study (ES). Postmenopausal women aged between 50 and 79 years were recruited from 1993 to 1998 at 40 clinical centers across the U.S. through several recruitment activities (e.g., mass mailings, community presentations) and included 93,676 racially and ethnically diverse postmenopausal women aged 50–79 years at baseline. Data were collected using in-person interviews,

Results

Descriptive statistics, displayed by categories of sedentary time, are shown in Table 1. The mean (SD) age of participants was 63.6 (7.4), and mean (SD) sedentary time was 8.5 (4.0) hours/day. In general, women who reported ≤4 hours/day of sedentary time were less likely to be white and had lower education compared with women in other categories of sedentary time: 70.9% of women with ≤4 hours/day sedentary time were white, compared with 85.5%, 86.3%, and 85.4% in women who reported >4–8 hours,

Discussion

Postmenopausal women who reported greater amounts of sedentary time had an increased risk of all-cause mortality after controlling for physical activity, physical function, and other relevant covariates. Mortality risk was modestly elevated in a dose–response manner and consistent across the causes of death examined, although CVD and CHD were not significant in the multivariate analysis after adjustment for multiple comparisons. The magnitude of the association between sedentary time and

Acknowledgments

Program Office: National Heart, Lung, and Blood Institute, Bethesda, Maryland: Elizabeth Nabel, Jacques Rossouw, Shari Ludlam, Joan McGowan, Leslie Ford, and Nancy Geller.

Clinical Coordinating Center: Fred Hutchinson Cancer Research Center, Seattle, Washington: Ross Prentice, Garnet Anderson, Andrea LaCroix, Charles L. Kooperberg, Ruth E. Patterson, Anne McTiernan. Medical Research Labs, Highland Heights, Kentucky: Evan Stein. University of California at San Francisco, San Francisco,

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      Studies with short follow-up had stronger magnitude of association in a dose–response manner (Fig. 3): 1–4 years [19,21,26,28,33,35,37] (HR, 1.58; 95% CI, 1.28–1.94); 5–9 years [14,16,18,22,23,25,29,31,32,38] (HR, 1.24; 95% CI, 1.16–1.31), and 10 years or more [15,17,20,24,27,30,34,36] (HR, 1.20; 95% CI, 1.10–1.31) of follow-up (Table 1). Studies that included older participants [16,21,28,29,37,38], did not adjust for any diseases/conditions in the models [14,15,18,25], did not exclude first years of follow-up [14–16,18,19,21–38], and did not exclude participants with diseases/conditions [15,19,21,24,26,28–37] showed stronger associations (Table 1). Overall, studies with higher risk of confounding due to pre-existing diseases [14–16,18,19,21,25,26,28,29,31–33,35,37,38] (HR, 1.40; 95% CI, 1.27–1.54) showed stronger association than lower risk studies [17,20,22–24,27,30,34,36] (HR, 1.18; 95% CI, 1.10–1.27).

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