Longitudinal Associations between Self-Rated Health and Performance-Based Physical Function in a Population-Based Cohort of Older Adults

<div><p>Background</p><p>Although self-rated health (SRH) and performance-based physical function (PPF) are both strong predictors of mortality, little research has investigated the relationships between them. The objective of this study was to evaluate longitudinal, bi-directional associations between SRH and PPF.</p><p>Methods</p><p>We evaluated longitudinal associations between SRH and PPF in 3,610 adults aged 65–89 followed for an average of 4.8 (standard deviation [SD]: 4.4) years between 1994 and July 2011 in the Adult Changes in Thought study, a population-based cohort in the Seattle area. SRH was assessed with a single-item question in the ACT study. Participants were asked at each evaluation to rate their health as “excellent”, “very good”, “good”, “fair”, or “poor” in response to the question “In general, how would you rate your health at this time”. PPF scores (ranging from 0–16, with higher indicating better performance) included walking speed, chair rises, grip strength, and balance.</p><p>Results</p><p>At the baseline visit, participants averaged 74.5 (SD: 5.8) years of age and 2,115 (58.6%) were female. In multivariable linear mixed models, PPF declined with age, with more rapid decreases associated with very good, good, and fair (vs. excellent) baseline SRH. Adjusted annual change in PPF was −0.17 points (95% confidence interval [CI]: −0.19, −0.15) for individuals with excellent baseline SRH and −0.21 points (95% CI: −0.22, −0.19) for participants with fair SRH. In multivariable generalized linear mixed models, lower baseline PPF quartiles were associated with lower odds of excellent/very good/good SRH at age 75, however, differences between baseline PPF quartiles diminished with age.</p><p>Conclusions</p><p>These results suggest that less than excellent SRH predicts decline in physical functioning, however, poor physical functioning may not predict change in SRH in a reciprocal fashion. SRH provides a simple assessment tool for identifying individuals at increased risk for decline in physical function.</p></div

Sex-specific Cutoffs for Scores (0 to 4) for Walking Speed, Chair Rises, Standing Balance, and Grip Strength Tests Based on Previously Published Scoring.

<p>Sex-specific Cutoffs for Scores (0 to 4) for Walking Speed, Chair Rises, Standing Balance, and Grip Strength Tests Based on Previously Published Scoring.</p

Generalized linear mixed model results for the associations between baseline PPF and age-related changes in SRH.^a

<p>Abbreviations: PPF, performance-based physical function; SRH, self-rated health.</p>a<p>Adjusted for age at baseline, sex, race, education, cognitive functioning, depressive symptoms, functional limitations, body mass index, alcohol use, smoking status, and exercise.</p>b<p>Estimates are standardized to the distribution of all covariates included in the model via indirect standardization.</p>c<p>P-values are for omnibus Wald test of any difference across categories of SRH.</p><p>Generalized linear mixed model results for the associations between baseline PPF and age-related changes in SRH.^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111761#nt112" target="_blank">a</a>}</p

Population mean trajectories of performance-based physical functioning (PPF) score modified by self-rated health (SRH).

<p>Average trends in PPF for adults aged 65–89 were estimated from a linear mixed model adjusted for age at baseline, sex, race, education, cognitive functioning, depressive symptoms, functional limitations, body mass index, alcohol use, smoking status, and exercise. SRH levels are depicted as: excellent = black solid, very good = grey solid, good = black dashed, fair = grey dashed, poor = black dotted. PPF scores (y-axis) ranged from 0 to 16; higher scores corresponded to better performance.</p

Trajectories^a in PPF and SRH level over follow-up for participants with two or more visits (N = 2,691).

a<p>No change, declined, and improved categories represent trajectories with one pattern; fluctuated categories represent trajectories with both decline and improvement (with either overall decline or another pattern).</p>b<p>dichotomized (healthy vs. unhealthy).</p><p>Note: N(% of 2,691) shown for each category.</p><p>Trajectories^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111761#nt104" target="_blank">a</a>} in PPF and SRH level over follow-up for participants with two or more visits (N = 2,691).</p

Population mean change in probability of excellent/very good/good (healthy) self-rated health (SRH) modified by quartiles of performance-based physical functioning (PPF).

<p>Average trends in PPF for adults aged 65–89 were estimated from a generalized linear mixed model adjusted for age at baseline, sex, race, education, cognitive functioning, depressive symptoms, functional limitations, body mass index, alcohol use, smoking status, and exercise. PPF Quartiles are depicted as: highest = black solid, upper-middle = grey solid, lower-middle = black dashed, lowest = grey dashed.</p

Linear mixed model results for the associations between baseline SRH and age-related changes PPF.^a

<p>Abbreviations: PPF, performance-based physical function; SRH, self-rated health.</p>a<p>Adjusted for age at baseline, sex, race, education, cognitive functioning, depressive symptoms, functional limitations, body mass index, alcohol use, smoking status, and exercise.</p>b<p>Estimates are standardized to the distribution of all covariates included in the model via indirect standardization.</p>c<p>P-values are for omnibus Wald test of any difference across categories of SRH.</p><p>Linear mixed model results for the associations between baseline SRH and age-related changes PPF.^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111761#nt108" target="_blank">a</a>}</p

Hypothesized relationships between SRH and physical function.

<p>Poor SRH is likely a proxy for an individual's underlying health state that is not captured by other measures. SRH then is statically but perhaps not causally associated with decline in physical function and an increased risk of death (pathway a). Alternatively, poor physical function may lead people to rate their health as poor (pathway b).</p

Participant baseline characteristics by self-rated health (N = 3,610).

<p>Abbreviations: SRH, self-rated health; CASI, Cognitive Abilities Screening Test; CESD, Center for Epidemiological Studies Depression Scale; ADL, Activities of Daily Living; IADL, Instrumental Activities of Daily Living.</p>a<p>Scores are scaled such that at baseline the mean score for the entire ACT cohort was 100 and the standard deviation was 15.</p>b<p>Health conditions included cancer, cerebrovascular disease, cardiovascular disease, diabetes, hypertension, and arthritis.</p><p>Participant baseline characteristics by self-rated health (N = 3,610).</p

Association between overweight (BMI ≥ 25 kg/m²) duration since age 18 y and risk of specific cancers, allowing for non-linear effects, with 95% CIs.

<p>HRs are adjusted for age, ethnicity, education, physical activity, smoking status, dietary intake (in kilocalories), and diet quality score. Restricted cubic splines were fitted with knots at 0, 8, and 40 y. <i>p</i>-Values are for nonlinearity. *All obesity-related cancers comprises postmenopausal breast cancer as well as cancer of the colon, rectum, liver, gallbladder, pancreas, endometrium, ovary, kidney, and thyroid.</p