This study found that low-intensity, but not high-intensity, caregivers declined more in performance-based functioning than noncaregivers did over a 2-year period. This excess decline was concentrated in the second year. Functional decline did not differ significantly between high-intensity caregivers and noncaregivers when we evaluated baseline caregiving status only or adjusted for current caregiving status at the first follow-up interview. However, in analyses restricted to respondents who maintained the same caregiving intensity level at the baseline and first follow-up interviews, performance-based functioning remained high among high-intensity caregivers throughout the follow-up period, while it declined among other respondents. Thus, caregiving intensity was associated with different trajectories of decline, although the absolute change in functional performance for each group was relatively small. These results support the healthy caregiver hypothesis more than the caregiver-stress hypothesis; the caregiver-stress hypothesis may be more appropriate for psychological outcomes rather than physical health outcomes.
The healthy caregiver hypothesis may be viewed as a variation of models of health benefits of physical activity. This hypothesis is based on observations that older adults who become caregivers are physically healthier than other older adults (9
) and that older caregivers are more active than noncaregivers (8
). The rationale is that caregivers who are healthier are able to undertake more caregiving tasks and that helping with more caregiving tasks reflects higher physical activity (either as a result of caregiving activities or in general). Accordingly, our results are consistent with studies finding that physically active elderly adults experienced less functional decline than their counterparts (15
) and, particularly, those who remained physically active experienced the least mobility decline (15
By contrast, the results of prospective studies on caregiving and physical health decline have been inconsistent (1
). Some studies support a caregiving stress hypothesis. For example, higher mortality rates were found for spouse caregivers strained by caregiving tasks but not for those not stressed by these activities (6
). However, this study also found that caregivers who helped a spouse with more ADL/IADL tasks reported fewer health risk behaviors over 1 year but did not exhibit changes in perceived health (27
). To our knowledge, only one study evaluated respondents’ physical health at more than 2 time points and used analytic techniques similar to those in our study (28
). That study found that self-reported physical symptoms increased more over 2 years in caregivers to a relative with dementia than in noncaregivers. Our results may have differed for several reasons: we used a performance-based measure rather than self-report, separated high- and low-intensity caregivers, and adjusted for health and other covariables. In addition, our sample was older, was restricted to women, and included caregivers to persons with dementia and nondementia diagnoses. It is also possible that older caregivers may develop more physical symptoms than noncaregivers do but maintain their physical functioning in order to meet their caregiving responsibilities.
The better functioning experienced by the high-intensity caregivers who continued at that level may be explained by several factors. These women may have had healthier constitutions, since better physical health predisposes elderly adults to become caregivers and remain as caregivers (9
). Likewise, they may have stayed healthier through the physical activity of caregiving or intentionally stayed fit to continue helping their care recipient. Also, their greater involvement in caregiving may have given them more satisfaction, resulting in health benefits (29
This study had several potential limitations. The caregiving-intensity variable was based on the median number of IADL and ADL tasks performed. Thus, each caregiving-intensity group included respondents who performed different types of tasks, reflecting different intensities. For example, helping with one ADL task, such as toileting, may be more time-consuming, physically difficult, and stressful than helping with one IADL task, such as managing finances. Moreover, although high-intensity caregivers reported the most stress, some high-intensity caregivers may have been less stressed by caregiving than some low-intensity caregivers. This variable did not account for number of hours per week that respondents performed these tasks, which also reflects caregiving intensity, and was assessed in previous studies (7
). Given the lack of a standard definition of caregiving intensity, number of caregiving tasks provides a more quantifiable, objective measure than asking respondents to rate the intensity of their caregiving involvement. Furthermore, performing more caregiving tasks has been correlated with more daily hours of caregiving (30
) and with higher stress in this study and others (31
Another potential limitation is that noncaregivers were not matched to caregivers on health status, and a third were enrolled 6 months after the caregiver was. We adjusted for baseline health and IADL limitations. Yet, it is unlikely that this lag time, or residual confounding by unmeasured factors (e.g., physical activity, psychological resilience), would have totally explained differences in functioning between caregivers and noncaregivers.
Loss to follow-up from mortality did not differ between caregivers and noncaregivers (4.7% vs. 5.3%, P
0.65). However, noncaregivers were more likely to lack follow-up performance-based functioning measures. Since poorer health was a reason for lacking these measures, our results most likely underestimated the true differences in decline between caregivers and noncaregivers.
Additionally, the sample comprised elderly women who were mainly white and high functioning, thus limiting generalizability of the results. However, these results apply to the majority of caregivers in the United States, who are elderly women (32
). It is unlikely that the mechanisms linking caregiving intensity to performance-based functioning would differ in other groups of older adults. Although the study design enabled us to observe yearly change in functioning over 3 time points, having more follow-up points would reveal more complex trends.
This study also had many strengths. The Caregiver-SOF sample comes from a large, multisite, community-based study of elderly women. Caregivers and noncaregivers were derived from the same source population, thus reducing possible biases related to recruiting caregivers from patient registries and noncaregivers from another source. The inclusion criteria required that caregivers were helping the care recipient with at least one IADL/ADL, thereby minimizing likelihood of misclassification of caregiver status and allowing categorization of high- and low-intensity caregivers by using criteria that can be replicated in other studies. Sensitivity analyses, in which we randomly recategorized 133 caregivers whose intensity values were near the cutpoint for high- and low-intensity and reran model A, showed that our results were robust to misclassification. Reassessment of caregiving intensity status at each annual interview provided insight into the impact of caregiving transitions versus continuation at the same intensity level. Finally, quantification of performance-based functioning was based on measures from previous studies (16
In conclusion, these results suggest that factors other than psychological stress influence performance-based functioning in older, high-intensity caregivers. Given that this study and others (1
) found that caregiving is stressful, future studies should explore the healthy caregiver hypothesis to better understand how caregiving affects physical health in older adults.