Health benefits of increased walking for sedentary, generally healthy older adults: using longitudinal data to approximate an intervention trial

Abstract

Background: Older adults are often advised to walk more, but randomized trials have not conclusively established the benefits of walking in this age group. Typical analyses based on observational data may have biased results. Here, we propose a "limited-bias," more interpretable estimate of the health benefits to sedentary healthy older adults of walking more, using longitudinal data from the Cardiovascular Health Study.

Methods: The number of city blocks walked per week, collected annually, was classified as sedentary (<7 blocks per week), somewhat active, or active (>or=28). Analysis was restricted to persons sedentary and healthy in the first 2 years. In Year 3, some became more active (the treatment groups). Self-rated health at Year 5 (follow-up) was regressed on walking at Year 3, with additional covariates from Year 2, when all were sedentary.

Results: At follow-up, 83.5% of those active at baseline had excellent, very good, or good self-rated health, as compared with 63.9% of the sedentary, an apparent benefit of 19.6 percentage points. After covariate adjustment, the limited-bias estimate of the benefit was 11.2 percentage points (95% confidence interval 3.7-18.6). Ten different outcome measures showed a benefit, ranging from 5 to 11 percentage points. Estimates from other study designs were smaller, less interpretable, and potentially more biased.

Conclusions: In longitudinal studies where walking and health are ascertained at every wave, limited-bias estimates can provide better estimates of the benefits of walking. A surprisingly small increase in walking was associated with meaningful health benefits.

Figure 1.

Schematic diagram of the limited-bias design (Year 4 omitted). Analysis is restricted to persons who were sedentary and healthy in Years 1 and 2. The primary analysis regresses Y (a binary variable indicating whether the person is healthy at Year 5) on X (walking level measured at Year 3). The “limited-bias” analysis controls for age, sex, race, and all the health variables at Year 2 and also for self-rated health at Year 2.5. Sedentary is defined as walking less than seven blocks per week, and active is walking 28 or more blocks per week at Year 3. Healthy (yes/no) is a binary variable denoting “not sick or dead” on the variable of interest. (Health at Year 2.5 is based on self-rated health because that was the only health variable measured semiannually. Walking was not measured at Year 2.5.)