This study found that elderly women caregivers had a lower adjusted risk of mortality over eight years than did non-caregivers. This result appeared to be due to caregivers who had low levels of general stress or caregiving-related stress: low-stress caregivers had 33% lower risk of mortality than did low-stress non-caregivers, and caregivers who were not stressed by caregiving tasks had a 43% lower mortality risk than all non-caregivers. By contrast, respondents with high stress had significantly higher mortality rates over the first three years of followup, regardless of caregiver status. These results supported our hypothesis that higher stress, rather than caregiving per se, is associated with increased rates of mortality. Furthermore, the effect of high stress on mortality was stronger among spouse caregivers than all caregivers combined (adjusted HR = 1.74 versus 1.44), supporting the assertion that comparing spouse caregivers to married non-caregivers may overestimate the adverse health effects of caregiving.
Our results confirm previous studies that found associations between chronic stress and increased mortality 6, 7
and are consistent with studies that did not find higher mortality rates among caregivers versus non-caregivers 10, 11, 13
. They are partially consistent with the Caregiver Health Effects Study (CHES), which found higher mortality rates among strained spouse caregivers 8
. The CHES study found no difference in mortality rates between caregivers who were not stressed by caregiving activities and non-caregivers, but caregivers who were stressed by these tasks had a 60% increased mortality risk over a 4-year period. In our sample, high perceived stress was associated with an 81% increased risk of mortality over a three-year period, and with a two-fold greater risk among spouse caregivers compared to married non-caregivers over the same period. Our results may have differed from studies that found elevated rates of mortality and CHD incidence 8, 9, 13
in that our sample included only older women who were followed for more years and was not restricted to married couples.
Our results fit a “Healthy Caregiver” effect, suggestive of the “Healthy Worker Effect.” The Healthy Worker Effect is a bias that leads to underestimating the health effects of harmful, work-related exposures so that the exposures appear to have smaller effects, or no effect on health outcomes 23
. This bias results from selection processes whereby healthier persons are more likely than comparison subjects to become employed and remain employed, and from not measuring health outcomes from the time employment began 23
. Indeed, previous studies found that healthier older adults were more likely to become caregivers and to remain as caregivers 24
. We found that caregivers were physically healthier than non-caregivers at baseline, and low-stress caregivers reported the fewest ADL and IADL limitations. Our results may not reflect a bias as much as an explanation for the relationships among caregiving, stress, and mortality. Although we could not adjust for health status at the commencement of caregiving, adjustment for several measures of baseline health reduced the protective effect of caregiving. This adjustment addressed one aspect of the Healthy Worker Effect, although residual confounding may have remained from unmeasured health variables. Further, our analyses separated the putative exposure, stress, from a marker of the exposure, caregiver status.
Our results also may reflect physical and psychological benefits of caregiving. Caregiving tasks may have kept respondents physically active, leading to a reduced risk of mortality 25, 26
. Caregivers also may have had stronger feelings of purpose than non-caregivers: elderly adults who feel more useful have lower mortality rates 27
. Additionally, satisfaction from caregiving experiences, especially among the low-stress caregivers, may have benefited health.
Alternatively, lower mortality among low-stress caregivers may have resulted from minimal caregiving involvement. Compared to high-stress caregivers, low-stress caregivers were less likely to care for a spouse, performed fewer caregiving tasks and reported more social contact. Thus, they may not have been the main caregiver, thereby incurring less stress from caregiving.
Our findings may have reflected the advanced age of the sample (mean age = 81 years). Women who survived to this age and could perform caregiving activities may have had exceptionally hearty constitutions. Nonetheless, similar results have been found in younger samples. 10, 11, 13
This study had several limitations. Caregiver-SOF was comprised of older women, who were mainly white. The results may not be generalizable to caregivers who are younger, minority, or male. However, most caregivers in the United States are elderly women, therefore these results apply to the majority of caregivers. This study assessed only all-cause mortality, and lacked sufficient power to conduct cause-specific analyses. In addition, caregiver status and stress were measured only at baseline, and we did not include length of time the respondent had been caregiving at baseline. Measuring caregiver status and intensity of caregiving at multiple timepoints could distinguish the relationships between continuation versus cessation of caregiving on mortality.
Nonetheless, this study had many strengths. The design allowed analyses of the separate effects of caregiving and stress on mortality. The Caregiver-SOF sample is a community-based sample of elderly women. All caregivers and non-caregivers came from the same source population, thereby reducing potential biases that may result from recruiting caregivers from patient registries and non-caregivers from other sources. The inclusion criteria required that caregivers were currently performing at least one IADL/ADL task for the care recipient, ensuring that all caregivers were actively involved in caregiving activities at baseline. These criteria resulted in a heterogeneous sample, thus increasing the generalizability of results to a wide variety of older women caregivers.
In conclusion, this study found that stress, rather than being a caregiver, increased mortality risk in elderly women. Moreover, caregivers who were not stressed had a lower mortality risk than non-caregivers. Because these results are based on a sample of elderly women, additional studies are needed to corroborate them. Future studies should include measures of general stress, health status, and physical activity to disentangle the effects of caregiving from stress, and to adjust for caregivers’ potential health advantage. Caregiver stress constitutes a growing public health concern. There are an estimated 44 million informal caregivers in the United States, and this figure is expected to rise 28
. This study underscores the importance of determining caregivers’ level of stress and recommendations to reduce it. Examples include interventions designed specifically for caregivers 29
or generic stress-reduction programs, such as mindfulness-based stress reduction, 30
that teach techniques to reduce stress in everyday life and therefore are adaptable to evolving caregiving situations. Such interventions may improve caregivers’ psychological status, as well as their physical health and ability to provide optimal care for their care recipient.