The 9 participating studies contributed a total of 34 485 participants (). Although most studies included men and women, 2 were sex specific.19,22
Of the total, 59.6% were women. There were substantial numbers of African American (n=3852) and Hispanic (n=2650) participants. The studies had a wide age range, including 1765 persons older than 85 years. Similarly, there was a wide range of gait speeds, from less than 0.4 m/s (n=1247) to more than 1.4 m/s (n=1491). Study follow-up time ranged from 6.0 to 21.0 years, with participants followed up for a mean of 12.2 and a median of 13.8 years. There were 17 528 total deaths across all studies, with rates varying from 18.40% to 91.87% in individual studies. Mortality rates appear to be related to length of follow-up ().
To assess consistency across studies, risk of death was estimated per 0.1-m/s higher gait speed. Age-adjusted HRs by study ranged from 0.83 to 0.94 and all were significant (P
<.001; ). We also examined the survival HRs for gait speed by study in subgroups, including age, sex, race/ethnicity, BMI, smoking history, use of mobility aids, prior hospitalization, self-reported health, functional status, and selected chronic diseases. There were consistent associations across studies, although given the large sample sizes, Q
statistics were often statistically significant (details available in eFigure 1A–M available at http://www.jama.com
). For the 3 levels of functional status (independent, difficulty with instrumental ADLs, and dependent in ADLs), the pooled HR per 0.1-m/s increase in gait speed for those who were independent was 0.92 (P
= .005), for those with difficulty in instrumental activities was also 0.92 (P
<.001) but was 0.94 (P
=.02) among those dependent in ADLs. Because physical activity measures were not sufficiently consistent across studies, effects could not be pooled. The Osteoporotic Fractures in Men (MrOS)19
and Hispanic Established Populations for Epidemiologic Studies of the Elderly (EPESE)8
used the Physical Activity Scale for the Elderly (PASE). When dichotomized at a score of 100 into low and high activity, MrOS had consistent and statistically significant HRs for low (HR, 0.85; 95% CI, 0.81–0.88) and high (HR, 0.87; 95% CI, 0.84–0.90) physical activity. In the Hispanic EPESE, the HR for low physical activity was significant (0.92; 95% CI, 0.88–0.96) but the HR for higher physical activity was not (0.99; 95% CI, 0.95–1.04). Pooled HRs for all subgroups except functional status were consistently in the range of 0.81 to 0.92 and all were significant (P
Age-Adjusted Hazard Ratio for Death per 0.1-m/s Higher Gait Speed
The overall HR for survival per each 0.1 m/s faster gait speed was 0.88 (95% CI, 0.87–0.90; P
<.001) when pooled across all studies using a random-effects meta-analytic statistical approach ( and eFigure 1 available at http://www.jama.com
). Further adjustment for sex, BMI, smoking status, systolic blood pressure, diseases, prior hospitalization, and self-reported health did not change the results (overall HR, 0.90; 95% CI, 0.89–0.91; P
<.001). Using data from all studies, we created for each sex, 5- and 10-year survival tables (, data derived from pooled Kaplan-Meier estimates evaluated at 5 and 10 years, presented in 3 age groups) and graphs (eFigure 3 and eFigure 4 predicted survival based on pooled logistic regression coefficients, data presented with age as a continuous variable). Gait speed was associated with differences in the probability of survival at all ages in both sexes, but was especially informative after age 75 years. In men, the probability of 5-year survival at age 85 ranged from 0.3 to 0.88 (eFigure 3A) and the probability of 10-year survival at age 75 years ranged from 0.18 to 0.86 (eFigure 4A). In women, the probability of 5-year survival remained greater than 0.5 until advanced age (eFigure 3B), but 10-year survival at age 75 years ranged from 0.34 to 0.92 and at age 80 years from 0.22 to 0.86 (eFigure 4B). Stratification by sex-specific median height failed to show systematic differences in survival rates between short and tall participants, so results presented are not stratified by height. Stratification by race/ethnicity (non-Hispanic white, black, Hispanic) suggested generally similar survival rates by gait speed among age and sex groups. Confidence intervals were often wide. In some subsets of slow walkers of Hispanic descent, survival rates were 10% to 20% higher than in other groups (eTable 2).
Five- and 10-Year Survival in Men and Women by Age and Gait Speed Group
We also used our analyses to estimate median years of remaining life based on sex, age, and gait speed. (, predicted survival data are based on an accelerated failure time model with Weibull distribution, with age as a continuous variable, and eTable 3, data are derived from pooled Kaplan-Meier estimates evaluated at 5 and 10 years in 3 age groups.) In the pooled sample, median survival in years for the age groups 65 through 74 years was 12.6 for men and 16.8 for women; for 75 through 84 years, 7.9 for men and 10.5 for women; and for 85 years or older, 4.6 for men and 6.4 years for women (eTable 3 available at http://www.jama.com
). Predicted years of remaining life for each sex and age increased as gait speed increased, with a gait speed of about 0.8 m/s at the median life expectancy at most ages for both sexes (; a PDF of enlarged graphs is available at http://www.jama.com
). Gait speeds of 1.0 m/s or higher consistently demonstrated survival that was longer than expected by age and sex alone. In this older adult population, the relationship of gait speed with remaining years of life was consistent across age groups, but the absolute number of expected remaining years of life was larger at younger ages. For 70-year-old men, life expectancy ranged from 7 to 23 years and for women, from 10 to 30 years.
Predicted Median Life Expectancy by Age and Gait Speed
To compare the 5-year survival predictive ability between demographics and gait speed vs other combinations of variables, we used areas under the ROC curve (C statistics) in logistic regression models for individual studies and pooled across studies (). Gait speed added substantially37
to age and sex in 7 of the 9 studies and in the pooled analysis. C statistics for age, sex, and gait speed were greater than those for age, sex, and chronic diseases in 4 of 9 studies, approximately equivalent in 5 studies and inferior in no studies. C statistics for age, sex, and gait speed were approximately equivalent to those for age, sex, chronic diseases, BMI, systolic blood pressure, and prior hospitalization in all 9 studies and in the pooled analysis. There were 4 studies that had sufficiently consistent data on functional status to create 3 categories: dependent in ADLs, difficulty with instrumental ADLs, and independent. For these studies, gait speed, age, and sex yielded a C statistic (0.741) that was not significantly different (P
=.78) from age, sex, mobility aids, and functional status (P
Predictive Accuracy for 5- and 10-Year Survival by Individual Study and Pooled Data Presented as Area Under the Receiver Operating Characteristic Curves
For 10-year survival, 6 studies had sufficient follow-up time to perform many of the analyses (). Gait speed added predictive ability to age and sex in 4 of 6 studies and in the pooled analysis. C statistics for age, sex, and gait speed were not significantly different from C statistics with all the other factors for any study nor for the pooled analysis. Three studies had sufficiently consistent data on functional status at baseline to allow pooling. Gait speed, age, and sex yielded a C statistic (0.734) that was not significantly different from age, sex, mobility aids, and functional status (0.732; (P=.95; ).
In addition, we used C statistics to assess the ability of usual gait speed to predict survival compared with other physical performance measures, such as fast gait speed and the Short Physical Performance Battery (SPPB), a brief measure that includes walk speed, chair rise ability, and balance. We assessed usual vs fast gait speed in the single study with both measures (Invecciare in Chianti18
study: usual, 0.727 [95% CI, 0.678–0.776]; fast, 0.684 [95% CI, 0.630–0.739]), suggesting that fast walks did not have an advantage in survival prediction over usual-paced walks. Gait speed was superior to the SPPB in the Hispanic Established Populations for the Epidemiological Study of the Elderly8
(gait speed, 0.617; 95% CI, 0.585–0.649; SPPB, 0.574; 95% CI, 0.539–0.649); was equivalent in the following 3 studies: Health, Aging, and Body Composition (ABC) study and ABC16
(gait speed, 0.579; 95% CI, 0.548–0.610; SPPB, 0.560; 95% CI, 0.528–0.592); Invecciare in Chianti (gait speed, 0.727; 95% CI, 0.678–0.776; SPPB, 0.738; 95% CI, 0.690–0.735); Predicting Elderly Performance study18
(gait speed, 0.667; 95% CI, 0.610–0.724; SPPB, 0.691; 95% CI, 0.637–0.744); and worse than SPPB in the Established Populations for the Epidemiological Study of the Elderly15
(gait speed, 0.638; 95% CI, 0.610–0.777; SPPB, 0.663; 95% CI, 0.636–0.691).