Informal care—unpaid care provided by families or non-family volunteers to fulfill patients’ need to accomplish activities of daily living (ADLs), such as bathing, dressing, and eating, or instrumental ADLs (IADLs), such as shopping, cooking, and managing money—is often necessary for patients with cardiovascular disease (CVD) or diabetes, especially for those who are elderly. Informal care improves the health and well-being of patients with CVD and diabetes.[1–3]Patients who received informal care were less likely to need physician visits and overnight hospital stays, compared with those who did not receive informal care.[4] Also, informal care reduces the high economic burden from utilization of formal care, such as nursing home care and home health services.[5, 6]

Patients’ quality of life could be improved by caregivers. However, the informal caregivers’ quality of life may deteriorate because of caregiving. The burden of informal care can be substantial among the elderly population with CVD or diabetes. Informal caregivers of CVD and diabetes patients frequently report various types of strains.[7, 8]Mental health burdens, such as distress, depression, and anxiety, are commonly reported by informal caregivers of CVD and diabetes patients.[9–11] Informal caregivers are also more likely to report poor physical health than non-caregivers.[12]

In addition, the economic burden of informal care for the elderly is substantial, estimated as $522 billion in the US in 2012.[13] While chronic diseases are the global leading causes of disability, CVD and diabetes are two of the most prominent chronic diseases closely linked together because of sharing common behavioral risk factors.[14] As global incidence and prevalence of CVD and diabetes are growing steadily, informal caregiving costs for CVD or diabetes patients become an important public health issue.[15] For instance, the prevalence of diabetes among adults were 4.7% in 1980 and became 8.5% in 2014 globally.[16] Diabetes is also known as a primary cause of blindness, kidney failure, and limb amputations, which require a significant amount of informal caregiving.[16] CVD, the number one cause of death, caused 31% of total global deaths.[17] Stroke caused 11.8% of all deaths in 2013 and the sixth leading cause of disability worldwide.[17, 18] Furthermore, the future economic burden of informal care is expected to increase rapidly because of the aging of the population, which results in a high prevalence of CVD or diabetes. In spite of its public health importance, the economic burden associated with informal care for patients with CVD or diabetes is often overlooked and has not been sufficiently addressed in economic literature, such as cost-of-illness studies and economic evaluation literature. No reviews exist that summarize current knowledge on this topic.

In this study we conducted a narrative literature review of studies about informal care costs for patients with CVD or diabetes to document the magnitude of economic burden and the methods used to derive estimates for informal care costs. We also determined and discussed factors which may explain the heterogeneity of the economic burden of informal care. Such information will be useful for improving estimates of economic burden associated with each disease and shaping future research in the field of economic costs of informal care. Although informal caregivers’ health issues and burden of those health problems could be substantial, costs of informal caregiving associated with health deterioration of caregivers were not examined in the current study because of limited existing research.

The review included English language peer-reviewed journal articles published between January 1995 and May 2015. We used PubMed, MEDLINE, and EconLit, and extended the search by checking the references of the relevant articles. Keywords for the search were informal care cost, costs of informal care, informal care, and economic burden. Among 141 potential abstracts from our search, we excluded review articles, editorials, and commentaries (Figure 1). We further excluded studies that (1) did not provide informal care time cost in monetary terms, (2) addressed measurement methods only, (3) examined factors that affect informal care only, and (4) did not investigate CVD or diabetes. Articles on neurological conditions were included if stroke was included as a part of the condition.

Ten articles met our selection criteria and were included for the review. Of the selected articles, six were for stroke [19–24], two were for heart failure [25, 26], and two were for diabetes [27, 28].

Results from this review show that burden of informal care is significant for stroke, heart failure, and diabetes patients. In addition, sizable heterogeneity was observed in estimated informal care burden for each of these conditions among reviewed studies. This variability was caused by several factors, which made it difficult to directly compare study results. First, choice of cost estimation method (OCA vs. RA) affects estimated costs of informal care because of different unit monetary values; this was often considered as a part of sensitivity analyses [19, 24, 27]. Additionally, the choice in using OCA or RA depends on survey questions about hours of informal care and availabilities of unit monetary values. OCA could be adapted when informal care hours were derived from foregone hours of doing other activities due to informal care, and values of foregone hours were known. In contrast, RA could be chosen when informal care hours were estimated from hours used to provide informal care activities, such as supporting ADLs and IADLs, and a market value of providing each informal care activity was available.

Some studies reported informal care burden attributable to a disease while others reported total informal care burden of patients with a disease or caregivers of those patients. Those two estimates were significantly different, and the purpose of those estimates were different as well. Estimation of total informal care burden is mainly used to understand the total burden for informal caregivers.[23] It can be helpful for developing policies supporting informal caregivers and for evaluating impacts of those policies. We found that all non-US studies, except one study from Australia,[19] reported total informal care burden in this review. On the other hand, cost of informal care attributable to a disease is a key component of cost-of-illness analyses and is helpful for understanding diminishable informal care burden when the disease is prevented.[28] All US studies in the current review reported informal care costs associated with a disease.

Another factor affecting estimated burden was whether the respondents were the caregivers or care recipients. It is known that there could be a reporting discrepancy between a caregiver and a care recipient.[29] Among the elderly population who have memory problems or cognitive disabilities, data from caregivers may be more reliable than the data from care recipients.[29] When a patient has multiple caregivers, however, interview all caregivers is difficult, and one caregiver may not know about another’s informal care burden. In that case, data from care recipients may be more complete. Thus, reports from both sides are required to reduce reporting biases and could provide a range of informal care burden estimates. In connection with respondents, some studies reported burden of informal care per caregiver and others reported the burden per patient. Per-patient estimates are best used for cost-of-illness analyses while per-caregiver estimates are useful for understanding the burden of caregivers.

Whereas most survey questionnaires asked about hours used to provide each informal care activity or overall hours to provide informal care activities, the selection of informal care activities included could affect estimated informal care burden. For instance, studies with ADLs and IADLs as informal care assisted areas may show fewer informal care hours than studies considering ADLs, IADLs, and HDLs. van den Berg and his colleagues showed that each activity area required a significant amount of informal care for stroke patients, while Chatterjee et al. supported that finding with diabetes patients.[24, 27] Developing a comprehensive standard set of informal care activities would help to avoid underestimation of informal care burden. Similarly, when the estimates are applied to cost-of-illness analysis, double counting issues must be considered. For instance, when assistance in household activities, such as housecleaning, washing, and cooking, is counted as burden of informal care, productivity losses in household activities among care recipients should not be included in cost-of-illness to avoid double counting.

Additionally, burden of informal care depends on disease severity. For instance, patients who had stroke-related health problems used more informal care than those who had stroke but without stroke-related health problems [20]. Also, diabetes patients using insulin treatment had higher needs of informal care than the diabetes patients without any medication for diabetes treatment.[28] Age, which increases limitations in ADLs and IADLs, could be another potential factor to affect the burden of informal care, especially total informal care costs.[30] Estimates of informal care hours and costs could also vary by study country. Patients in developing countries may use more informal care hours than patients in developed countries. The monetary value of informal care in developing countries, however, could be lower than the value in developed countries because of lower hourly wages in developing countries. For instance, Riewpaiboon et al. indirectly supported this point by showing that costs of informal care in urban area (developed area) was higher than that in rural area (developing area) in Thailand. [23]

Results of this review indicate that informal care costs for stroke, heart failure, and diabetes patients are substantial and should be included in cost-of-illness literature. Several factors, including cost estimation methods, data sources, study location, and severity of disease, may affect estimates of informal care burden. Although various methods are already developed to estimate informal care burden, no consensus exists about analytic methods. It is important to conduct sensitivity analyses using various methods. However, it is also important to gain consensus on estimation methods, especially for a comparison of estimates from different diseases, which is important for decision makers.

To better integrate the cost of informal care into cost-of-illness literature, we believe standardizing methods for estimating informal care costs is critical. Based on our review, we suggest the following standards: (1) conduct proper analysis for estimating disease-attributable informal care cost to avoid overestimation resulting from multiple diseases per patient, (2) collect patient-level data that include all informal caregivers’ burden, (3) use a comprehensive set of help areas and less memory-dependent collection methods, and (4) conduct sensitivity analysis using various cost estimation methods and data assumptions.

Improving the quality of research to collect accurate hours of informal care and investigation of proper ways to estimate costs could improve the cost estimates. For instance, all the reviewed studies used informal care hours from a retrospective time diary. The quality of data depended entirely on the interviewee’s recall ability. Monitoring respondents or gathering survey data using a leave-behind time diary, which leaves a time diary form with a respondent and asks him or her to complete the form on appointed days, could avoid possible biases and improve data quality. Sample size and representativeness of samples also could be an issue. Because many studies used samples with fewer than 500 subjects, it is important to develop a sufficient data set for estimation.

Increasing data quality is an important step for producing robust study results and expediting the integration of these costs into economic evaluations as well as cost-of-illness analyses. Since informal care costs associated with CVD or diabetes are substantial, including accurate cost estimates prevents underinvesting on prevention or intervention strategies for these diseases.