Fredman L, Cauley JA, Satterfield S, Simonsick E, Spencer SM, Ayonayon HN, Harris TB, Health ABC Study Group. Caregiving, Mortality, and Mobility DeclineThe Health, Aging, and Body Composition (Health ABC) Study. Arch Intern Med. 2008;168(19):2154-2162. doi:10.1001/archinte.168.19.2154
Although caregivers report more stress than noncaregivers, few studies have found greater health decline in older caregivers. We hypothesized that caregivers may be more physically active than noncaregivers, which may protect them from health decline.
The sample included 3075 healthy adults from the Health, Aging, and Body Composition (Health ABC) Study. They were aged 70 to 79 years in April 1997 to June 1998 and resided in Memphis, Tennessee, or Pittsburgh, Pennsylvania. Caregivers (680 [22.1%]) were participants who provided regular care or assistance for a child or a disabled or sick adult. Outcomes included all-cause mortality and incident mobility limitation (defined as difficulty walking one-quarter mile or climbing 10 steps on 2 consecutive semiannual contacts) during 8 years. Total physical activity included daily routine, exercise, and caregiving activity.
Overall, 20.6% of caregivers died and 50.9% developed mobility limitations vs 22.0% and 48.9% of noncaregivers, respectively. Associations differed by race and sex. Mortality and mobility limitation rates were 1.5 times higher in white caregivers (eg, among white female caregivers, adjusted hazard ratio for mortality, 1.6; 95% confidence interval, 1.0-2.5) but not for black female caregivers vs noncaregivers (adjusted hazard ratio for mortality, 0.9; 95% confidence interval, 0.5-1.4). Physical activity mediated these associations in most race-sex groups. High-intensity caregivers (ie, caregiving ≥24 hours per week) had elevated rates of decline when adjusted for physical activity but lower rates when not adjusted for activity.
Older white caregivers have poorer health outcomes than black female caregivers. Physical activity appears to mask the adverse effects of high-intensity caregiving in most race-sex groups.
Most studies1 of informal caregiving and health outcomes have been guided by psychosocial stress theories, but this framework may not sufficiently explain the association between caregiving and health decline in older adults. Although studies2,3 have found poorer immune status in caregivers compared with noncaregivers, evidence that caregiving increases disease incidence or mortality has been inconsistent.4 Three studies found that caregivers to an ill or disabled spouse had elevated rates of all-cause mortality5,6 and fatal and nonfatal coronary heart disease (CHD).7 These associations, however, were limited to spousal caregivers who were stressed by caregiving activities6 and women who performed caregiving tasks for 9 or more hours per week.7 In contrast, among women caregivers, stress did not increase the rate of CHD, and caregivers to a friend or nonspouse relative had lower rates of CHD than noncaregivers.7 These inconsistent results suggest the need to examine factors that may influence the association between caregiving and health decline in older adults, particularly race, sex, and the overall level of physical activity of caregivers and noncaregivers.
Incorporating physical activity into studies of caregiving outcomes may provide a more accurate description of how caregiving affects physical health. Moderate physical activity protects against the major health outcomes on which caregivers and noncaregivers have been compared: heart disease,8 mortality,9 and incident mobility disability.10 Physical activity is also associated with lower stress and depressive symptoms,11 which are uniformly higher in caregivers than noncaregivers.4 Moreover, elderly caregivers report more overall physical activity than same-aged noncaregivers,12 and elderly persons who become caregivers and who continue caregiving have better physical functioning than noncaregivers.13 Thus, if physical activity is correlated with better health and healthier elderly persons are more likely to become caregivers and to perform more caregiving activities, then ignoring physical activity could underestimate the association between caregiving and health decline. To date, to our knowledge, no study has considered the potential mediating effects of overall physical activity on this association.
Evidence has also indicated that the association between caregiving and health decline may differ by race and sex. Caregiving involvement and the familial relationship of caregivers to the care recipient vary by race and sex. Specifically, caregivers who are black14,15 and female16,17 spend more hours per week in caregiving activities. Also, black caregivers are more likely to take care of grandchildren,18 nonspouse relatives, and friends,15 whereas whites and females are more likely to be the main caregiver for a relative who needs assistance.17 Furthermore, caregivers who are white14 and female4 report higher levels of stress and depressive symptoms than other caregivers. Finally, physiologic responses to caregiving differ: male caregivers have poorer immune response19 and are more likely to develop CHD indicators20 than female caregivers, and black female caregivers show more cardiovascular and cortisol reactivity than their white counterparts, despite reporting less stress.21 Thus, comparing results across race-sex categories could identify groups of vulnerable caregivers and suggest mechanisms by which caregiving may affect health decline.
The present study used data from the Health, Aging, and Body Composition (Health ABC) Study to evaluate the association between caregiving and health decline, measured by all-cause mortality and incident mobility limitations. These end points were chosen to permit comparisons with previous studies5,6 and because mobility limitations represent a critical aspect of quality of life in older adults and are likely to predict whether caregivers can continue to participate in caregiving activities. Analyses were performed within race-sex subgroups.
This study tested the following hypothesis. Overall, caregivers and noncaregivers will not differ in rates of all-cause mortality or incident mobility limitations. However, when adjusting for total amount of physical activity, caregivers will have higher rates of these health outcomes than noncaregivers.
The study population consisted of 3075 well-functioning white and black men and women aged 70 to 79 years participating in the Health ABC Study. Potential white participants were identified from a random sample of Medicare beneficiaries who lived in designated zip codes surrounding Pittsburgh and Memphis, Tennessee. Black participants were recruited from all age-eligible residents in these zip codes. Eligibility criteria included self-report of no difficulty walking one-quarter of a mile, climbing 10 steps, or performing basic activities of daily living, no reported need of walking aids, no known life-threatening cancers, and no plans to move from the area for 3 years. The baseline home interview and clinic-based examination took place between April 1997 and June 1998. All respondents provided written informed consent, and all protocols were approved by the institutional review boards at the study sites. Follow-up clinical examinations or home-based interviews were performed annually, and short telephone interviews were performed at 6 months between each annual interview. For the present study, caregiver status and information on covariates came from the baseline interview.
Caregiver status and level of caregiving intensity were ascertained from responses to the question, “Do you currently provide any regular care or assistance for a child or a disabled or sick adult?” Participants who answered affirmatively were asked how many hours per week they provided that care. Caregivers were categorized according to tertiles of caregiving intensity based on the sample-based distribution of the number of hours per week they provided care: low (1-7 hours per week), medium (8-23 hours per week), and high (24-168 hours per week).
All-cause mortality was documented through August 9, 2005. Survival time was calculated as the number of days from the baseline interview until mortality or the last known date of contact with the 181 respondents (5.9%) with missing information on vital status. Information on death was obtained from family members, local obituaries, and the Social Security Administration Web site. All deaths were confirmed by death certificates, which were obtained from family members or the state office of vital records.
Incident mobility limitation was based on reported difficulty walking one-quarter mile or climbing 10 steps without resting at 2 consecutive semiannual follow-up interviews.10 Because the eligibility criteria for the Health ABC Study required respondents to be free of these limitations at baseline, time to incident mobility limitation was calculated as the number of days from the baseline interview to the first interview at which difficulty performing the activity was reported by the respondent or his/her proxy.
Demographic variables included the respondent's age, race (respondents self-identified as white or black), sex, highest education level (postsecondary school vs less education), marital status (married vs other), and Health ABC Study site.
We classified respondents according to whether they lived with relatives or friends but not a spouse. Respondents who lived alone or only with a spouse were categorized as not living with nonspouse others. We created this variable to capture participants who had an opportunity to be caregivers to grandchildren and relatives other than a spouse because they lived in the same household.
Presence of prevalent medical conditions was a dichotomous variable based on the presence of 1 or more of the following conditions: respondent's self-report of CHD, cerebrovascular disease, congestive heart failure, pulmonary disease, or peripheral arterial disease; self-report or taking medications for diabetes mellitus; electrocardiographic evidence of a myocardial infarction; clinical osteoporosis; or diagnosis of knee or hip osteoarthritis.
The 10-item version of the Center for Epidemiologic Studies–Depressive Symptoms Scale was used.22 Response options on a 4-category scale ranged from experiencing the symptom “rarely/none of the time” to “most or all of the time.” Respondents were categorized according to whether their scores were 10 or greater, which indicated being at risk for depression.
Body mass index (calculated as weight in kilograms divided by height in meters squared) was determined from measured height and weight obtained at the baseline clinical examination.
Total physical activity was measured by a self-report questionnaire designed for the Health ABC Study based on validated physical activity questionnaires and described previously.10 Participants indicated whether they had performed activities during the past 7 days as part of their daily routine and for leisure-time exercise, along with the amount of time spent in each activity. These activities included gardening, heavy chores, light housework, grocery shopping, laundry, climbing stairs, walking for exercise and for other purposes, and moderate- and high-intensity exercise. In addition, time spent in paid work, volunteer work, and caregiving activities was documented. A metabolic equivalent value in kilocalories per week per kilogram of body weight was determined for each activity. A total physical activity score was calculated as the sum of the metabolic equivalent values for each activity (those activities performed as part of caregiving and those performed during the respondent's daily routine and leisure activities) multiplied by the participant's body weight in kilograms.
Physical activity spent in family care activities was calculated for respondents who reported that they were caregivers in the past week, using the methods described herein for calculating total physical activity. This measure was calculated to separate the amount of physical activity attributable to caregiving vs noncaregiving activities.
Characteristics of caregivers and noncaregivers were compared in the total sample and within each race-sex group using t tests for continuous variables and χ2 tests for categorical variables. Cox proportional hazards models were performed to compare rates of mortality and incident mobility limitation between caregivers and noncaregivers. Person-time of follow-up was measured as the number of days from the baseline interview until date of death or date of the first interview of 2 consecutive reports of a mobility limitation. For respondents who were lost to follow-up or who remained in the study throughout the follow-up period without developing these outcomes, person-days were measured from the baseline interview to the date of last contact.
Three separate proportional hazards models were performed for each outcome. Model A adjusted for Health ABC Study site and age at baseline only. Model B adjusted for Health ABC Study site, all confounders, and significant covariates except for total physical activity. Model C added the total physical activity variable to model B. Models B and C were derived by backward elimination procedures. First, all potential confounders were added to a model that included the caregiver variable and Health ABC Study site. Second, variables that were not statistically significant and contributed the least were excluded one at a time, as long as their exclusion did not meaningfully change the association between caregiving and the outcome of interest. Hazards ratios (HRs) and 95% confidence intervals (CIs) were calculated. Noncaregivers were the reference group in each model. Analyses of caregiving intensity included an indicator variable for each level (ie, low, medium, and high) to allow for comparisons with the noncaregivers while simultaneously adjusting for the other levels of caregiving intensity.
To determine whether associations differed by race-sex group, we tested the significance of a 3-way interaction term in the multivariate models for the total sample. These models included terms for race, sex, and caregiver status, race × sex interaction, and race × sex × caregiver status interaction. The 3-way interaction term was statistically significant (P < .01) in the models on mortality and on incident mobility limitations, regardless of whether they adjusted for physical activity. Therefore, analyses were performed within race-sex strata. A commercially available software program (SAS, version 9.1; SAS Institute Inc, Cary, North Carolina) was used for all analyses.
The baseline sample included 3075 participants (51.5% were women and 58.3% were white) with a mean age of 73.6 years. The sample characteristics are described in more detail elsewhere.23 Approximately 22% (22.3%) of the respondents reported being a caregiver to a child or disabled adult. Black women were most likely to be caregivers (28.8%) and to spend the most time caregiving. Nineteen percent of black women spent 8 or more hours a week performing caregiving activities, whereas white men were least likely to be caregivers (18.2%) and less involved in caregiving activities than other race-sex groups.
Overall, caregivers were slightly younger than noncaregivers, were more likely to be married and/or live with others, and had completed fewer years of education (Table 1). Caregivers and noncaregivers did not differ in physical or mental health characteristics. However, caregivers in each race-sex group were significantly more physically active than noncaregivers. When kilocalories expended in caregiving activities were excluded from total physical activity, these differences were diminished slightly, but in all subgroups except black men, caregivers remained more physically active than noncaregivers.
As indicated in Table 2, 20.6% of the caregivers and 22.0% of the noncaregivers died during the follow-up period. The mean (SD) length of follow-up among respondents who died, lacked vital status data, or remained alive was 4.5 (2.0) years, 6.2 (1.8) years, and 7.3 (0.4) years, respectively. Mortality in caregivers and noncaregivers differed substantially across race-sex groups. For example, caregivers had a higher unadjusted risk of mortality compared with noncaregivers among white men (28.2% vs 21.4%) but a slightly lower risk among black men (30.2% vs 35.4%) and less than half the risk among black women (13.0% vs 23.6%). Caregiving intensity did not appear to be associated with mortality; in most race-sex groups, high-intensity caregivers had a lower unadjusted risk of mortality than other caregivers.
Similar associations were observed in site- and age-adjusted Cox proportional hazards models (Table 3, model A). Notably, white male caregivers had significantly higher mortality rates than noncaregivers, whereas black female caregivers had a lower rate. In all race-sex groups except for white men, high-intensity caregivers exhibited the lowest mortality rates. These associations were not substantially changed when adjusted for site, age, and other significant covariates except for physical activity (model B). However, adjusting for total physical activity in addition to all significant covariates resulted in a higher mortality rate among caregivers overall and for most levels of caregiving intensity for white male and female participants (model C). Moreover, high-intensity caregivers had elevated mortality rates compared with noncaregivers in all race-sex groups except for black males.
The associations between caregiving and incident mobility limitation were similar to those for caregiving and mortality (Table 2 and Table 4). White male and female caregivers had higher rates of incident mobility limitation than their noncaregiver counterparts, but caregiving appeared to be protective in black female caregivers and was not associated with decline in black male caregivers. Caregiving intensity was not associated with developing mobility limitations. Adjusting for significant confounders except for physical activity had minimal effects on these results (model B). However, when adjusted for total physical activity and other confounders (model C), white male and female caregivers had higher rates of incident mobility limitation than noncaregivers, and the apparently protective effect of caregiving among black female caregivers was attenuated. Similar to the mortality results, high-intensity caregivers had elevated rates of incident mobility limitation compared with noncaregivers in all race-sex groups. For the total sample, when adjusting for physical activity and other covariates, a non–statistically significant trend was found toward a dose-response association between intensity of caregiving and incident mobility limitation (HR ranged from 1.09 [95% CI, 0.90-1.33] to 1.45 [95% CI, 1.14-1.83] in low-intensity and high-intensity caregivers, respectively).
This study found that among healthy community-dwelling elderly adults, caregivers had modestly elevated rates of mortality and incident mobility limitation. Performing caregiving activities at least 24 hours per week was associated with an increased rate of mobility limitation but not mortality. The higher rates of health decline observed among white caregivers are consistent with previous research that found that older stressed caregivers to a spouse were 1.63 times more likely to die than married noncaregivers.6 We found no association between caregiving and health decline among black males, whereas black female caregivers had lower rates of health decline than noncaregivers, although these associations were attenuated when adjusted for total physical activity. Furthermore, in most race-sex groups, adjusting for total physical activity plus other confounders resulted in higher rates of health decline in high-intensity caregivers compared with noncaregivers, which was not observed in analyses that lacked adjustment for physical activity. These results complement findings that caregiving for a spouse at least 9 hours per week, but not less often, was associated with higher rates of CHD.7
To our knowledge, this is the first study on caregiving and physical health decline within different race-sex groups. Regardless of the race-sex group, elderly caregivers who were most intensely involved in caregiving had the highest rates of mobility limitation compared with noncaregivers when adjusting for physical activity. These results indicate that caregiving may have deleterious effects on physical health and quality of life even if it is not a strong risk factor for mortality: mobility limitations are costly, increase the risk of mortality,24 and impair a person's ability to provide optimal care for the care recipient. These findings extend results of previous studies of caregiving effects on mortality5,6 and CHD incidence.7
The differences observed across race-sex groups support studies that found variations in caregiving involvement14- 17 and psychological4,14 and physiologic19- 21 effects of caregiving by these demographic categories. These results also suggest hypotheses to explain the relationship between caregiving and health outcomes. The higher rates of health decline among white male caregivers support studies19 that found poorer immune response in male vs female caregivers. Although white men may be less involved in caregiving and report less stress than women, caregiving may have a stronger influence on their physical health because they may have fewer resources (such as social networks) to buffer its effects. The protective associations between minimal-moderate caregiving and health outcomes among black female caregivers are consistent with studies that found healthier persons are more likely to become caregivers15 and that the physical effort of caregiving activities may benefit health.12 Moreover, these caregivers are more likely to care for relatives other than a spouse. If they are raising a grandchild or great-grandchild, they may find greater satisfaction from care giving or be motivated to stay healthy, which could explain these results.
This study was limited by its measure of caregiver status and lack of measures describing the caregiving situation. Respondents may have interpreted the caregiver status variable as providing regular child care rather than taking care of a child who was sick or disabled. This possibility is supported by the fact that the highest percentage of caregivers were among black women, who are most likely to take care of grandchildren.18 Classifying these women as caregivers may have underestimated the effect of caregiving on health decline. In addition, the number of hours per week in caregiving activities served as a proxy for caregiving stress and may not have reflected the overall stressfulness of caregiving or the magnitude of care. For example, caregivers who are stressed because they care for a person with advanced dementia may perform fewer hours of caregiving because relatives or formal caregivers assist with these activities. This study also could not analyze caregiving-related factors and health decline because of the absence of measures that have been associated with caregiver stress in other studies, such as the caregiver's relationship to the care recipient (eg, spouse), the care recipient's dementia status, and the activities of daily living performed by the caregiver. Nevertheless, few previous studies of caregiving and health decline included these measures.
Another concern was that the results adjusted for total physical activity may have reflected better general health. We reran model C, replacing the physical activity variable with other health measures (ie, self-rated health status, ease in walking 1 mile or up 2 flights of stairs, and walking speed for 400 m or 20 m). These measures had weak to no impact on associations between caregiving and health decline, supporting the conclusion that the caregivers' overall physical activity mediates their health outcomes. A final limitation was the lack of a measure of general stress that would have allowed us to analyze whether associations with health outcomes were due to caregiving, stress, or their combination.
Nonetheless, this study had several strengths. The Health ABC Study sample included healthy respondents who had no mobility limitation at baseline. Thus, unlike some other community-based studies,15 caregivers were not necessarily healthier than noncaregivers at baseline, and we were able to evaluate incident functional decline. The large number of black and male respondents allowed us to compare associations across race-sex subgroups. The Health ABC Study sample constitutes a population-based sample of community-dwelling adults. Thus, the results are not likely to be biased by the types of caregivers who would volunteer for studies, and are generalizable to community-dwelling adults in their 70s. Finally, the study included measures of physical activity, health, and demographic characteristics that allowed us to adjust for overall physical activity and important confounders.
In conclusion, caregiving was associated with higher rates of mortality and incident mobility limitation in certain race-sex groups. Adjustment for physical activity revealed adverse effects of caregiving that were not observed when physical activity was excluded. Given the increasing number of elderly caregivers in the United States,16 these results underscore the potential toll of caregiving on physical health and the need for services to reduce caregivers' stress and maintain their health and ability to provide optimal care for their family members.
Correspondence: Lisa Fredman, PhD, Department of Epidemiology, Boston University School of Public Health, 715 Albany St, Room TE329, Boston, MA 02118 (email@example.com).
Accepted for Publication: April 21, 2008.
Author Contributions: Dr Fredman had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Fredman and Harris. Acquisition of data: Cauley, Satterfield, Simonsick, and Harris. Analysis and interpretation of data: Fredman, Spencer, Ayonayon, and Harris. Drafting of the manuscript: Fredman. Critical revision of the manuscript for important intellectual content: Cauley, Satterfield, Simonsick, Spencer, Ayonayon, and Harris. Statistical analysis: Fredman. Obtained funding: Cauley and Harris. Administrative, technical, and material support: Cauley, Satterfield, Simonsick, Ayonayon, and Harris.
Health ABC Study Group Investigators: Anne B. Newman, MD, MPH (principal investigator); Piera Kost (study coordinator), University of Pittsburgh, Pittsburgh, Pennsylvania; Suzanne Satterfield, MD, DrPH; Frances A. Tylavsky, DrPH; Stephen B. Kritchevsky, PhD (former Memphis prinicipal investigator, now at Wake Forest School of Medicine) (principal investigators), Susan Thomas (study coordinator), University of Tennessee, Memphis; Steven R. Cummings, MD, Michael C. Nevitt, PhD (principal investigators), Susan M. Rubin, MPH (project director), University of California, San Francisco (Health ABC Coordinating Center); Tamara B. Harris, MD (National Institute on Aging project officer), Melissa E. Garcia, MPH, National Institute on Aging (Project Office), Bethesda, Maryland.
Financial Disclosure: None reported.
Funding/Support: This research was supported in part by the Intramural Research Program of the National Institutes of Health (NIH), National Institute on Aging (NIA), by NIA contracts N01-AG-6-2106, N01-AG-6-2101, and N01-AG-6-2103, and by grant R01 AG18037 from the NIH, NIA.