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RESEARCH ARTICLE |
1 Department of Epidemiology, Aichi Prefectural College of Nursing and Health, Nagoya, Japan.
2 Gerontological Nursing, Aichi Prefectural College of Nursing and Health, Nagoya, Japan.
Address correspondence to Kazushi Okamoto, MD, Aichi Prefectural College of Nursing and Health, Tougoku, Kamishidami, Moriyama-ku, Nagoya, 463-8502, Japan. E-mail: okamoto{at}aichi-nurs.ac.jp
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Abstract |
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Recently, older adults have been encouraged to participate in activities that make use of their skills and abilities in their use of free time as a result of a higher life expectancy, and the number of those actively participating in social activities and volunteer work (older adults who are healthy and active are called "Silver" in Japan) has increased (The Cabinet Office in Japan, 2002
). Japanese society has traditionally had a general atmosphere in which older adults often take care of their subordinates in both social and personal matters. Moreover, older Japanese adults have a deep-seated feeling that they do not forget the favors received from others, and they advocate returning favors. This may result from the expression of a fundamental desire to do something useful for others rather than for oneself alone in old age. Such a sense, that is, one's usefulness to others, is also reported to affect the level of psychological functioning and quality of life, and it decreases the risk of morbidity (Ekerdt, Bosse, & Levkoff, 1985).
Several cross-sectional studies have demonstrated that such subjective usefulness is strongly related to physical and psychological health, and it may be a good predictor of overall well-being (Bachman, 1970; Butler & Gleason, 1985; Ranzijn, Keeves, Luszcz, & Feather, 1998; Ryan & Frederick, 1997; Ryff, 1989). These findings strongly suggest that subjective usefulness may be a key factor in maintaining and promoting self-rated health and general well-being. Recently, researchers reported self-perceptions of aging including the concept of usefulness to influence longevity and to predict functional health over an 18-year period (Levy, Slade, Kunkel, & Kasl, 2002). However, they have not prospectively commented on the effect of the sense of one's usefulness alone on longevity among healthy older adults. Therefore, we investigated such relationships between the evaluation of subjective usefulness and mortality among older participants in Japan.
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METHODS |
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Measures
We determined the vital status (alive or deceased) of study participants during 6 years of follow-up from August 1995 through September 2001, and we confirmed deaths both by inquiries of older participants or family members and by obtaining data from official death certificates. The completion rate of follow-up on deaths was almost 100%. Interviewers obtained informed consent from each study participant after a verbal explanation of the study purpose and methods, and they gathered a review of personal data at the end of follow-up.
We assessed subjective usefulness by using the following single-question item: "How do you evaluate your own present usefulness to others and society?" The response categories were "quite a bit," "some," "a little," and "not at all." Because there was low frequency in the "not at all" category, we classified our participants into three categories: "quite a bit," "some," and "a little or not at all." In multivariate analyses, we further categorized subjective usefulness as "high" (quite a bit or some) versus "low" (a little or not at all).
We assessed self-rated health on the basis of responses to this statement: "How do you evaluate your present health (excellent, good, fair, or poor)?" We considered those who responded "excellent" or "good" to be in good health, whereas we judged those who responded "fair" or "poor" to be in suboptimal health.
The sociodemographic variables included in this study were age, gender, and marital status (married vs unmarried). We assessed medical status on the basis of the presence or absence of the following chronic medical conditions during the previous 12 months: hypertension, diabetes mellitus, angina, myocardial infarction, stroke, bronchitis, asthma, hepatitis B or liver disease, anemia, circulatory troubles in the extremities, and hip fractures or arthritis. We considered these conditions to be present if participants reported having been diagnosed by a doctor or if they had been hospitalized for those conditions.
We assessed physical activities on the basis of response to this statement: "How often do you exercise in your usual day?" Responses presented were "less than once a week," "1–2 times per week," "3–4 times per week," and "almost everyday." We considered those who responded "less than once a week" or "1–2 times per week" to be inactive, whereas we categorized those who responded "3–4 times per week" or "almost everyday" as active. We classified the number of medical conditions as either 0 or 1 or more. We defined symptomatic depression as two or more of the following symptoms: feeling lonely, having difficulty in falling asleep, being unwilling to do things or having a lack of energy, feeling depressed, and experiencing nervous tension or nervousness. We assessed contact with network resources on the basis of responses to this statement: "How often do you talk with friends and relatives on a typical week?" The possible responses were "almost every day," "once or twice a week," "rarely," and "never." Because there was a low frequency of responses in the "never" category, we grouped it into a single category with the "rarely" responses. We defined social role as one or more of the following activities: volunteering, attending a community service organization, and making a financial contribution to a community association.
Statistical Analysis
We estimated the survival functions for each covariate by using the Kaplan–Meier product-limit method. We assessed the association between subjective usefulness and mortality by using the odds ratio (OR) and 95% confidence interval (CI) in Cox's hazard model in which subjective usefulness was defined in the terms of categorical variables. In these analyses, we considered the participant's age at a baseline for each participant, and we censored participants at the last time their status "alive" or "deceased." We then used four sequential hazard models to analyze the relationships between self-perceived usefulness and mortality. We performed all calculations with SPSS Version 10.0 for Windows (Statistical Package for the Social Sciences, SPSS Inc., Chicago, IL), using the LOGISTIC procedures.
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RESULTS |
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Table 2 shows the hazard risks and confidence intervals for mortality in 2001 associated with 1995 subjective usefulness. In all four models, subjective usefulness was shown to be protecting against mortality. In the fully adjusted model (Model 4), the adjusted hazard ratio of mortality was 2.24 times higher among those who rated their usefulness as "a little or not at all" compared with those with a "quite a bit" rating, which amounted to a statistically significant difference.
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DISCUSSION |
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A methodological issue arose from the fact that we measured subjective usefulness with a single-item question, not by using a multidimensional scale including complex terms. This is because a single-item question is more likely to simply and directly assess the sense of subjective usefulness than a multidimensional scale. Moreover, we found high agreement in the degree of subjective usefulness between a single-item question and the six-item scale proposed by Ranzijn and colleagues (1998) among 100 individuals who were randomly selected from all study participants (Spearman correlation coefficient, r =.76; 
= 0.81). These findings suggest that the effect of using a single-item question does not make a major difference.
In this study, we cross-sectionally demonstrated a significant positive relationship between subjective usefulness and self-rated health. Dua (1995) reported that negative affect was the best predictor of prospective health. According to Ryan and Frederick (1997), such subjective vitality and subjective usefulness were found to be highly salient and strongly related to physical and psychological health. Accordingly, these findings might provide a more likely explanation for our results.
We also observed an inverse relationship between subjective usefulness and mortality. A number of studies have also demonstrated that poor self-rated health is significantly associated with an increased mortality (Blazer & Houpt, 1979; Heidrich, Liese, Lowel, & Keil, 2002; Heistaro, Jousilahti & Lahelma, 2001). Accordingly, it is quite likely that the relationship between subjective usefulness and mortality may be confounded by self-rated health. However, significant relationships remained even after adjustment for self-rated health, indicating that subjective usefulness affects the mortality among older adults independent of self-rated health.
A few studies have demonstrated that volunteering exerts a protective effect against mortality among older adults (Chambre, 1993; Hunter & Linn, 1980–1981; Musik, Herzog, & House, 1999; Ward, 1979). According to Stevence (1980), involvement with others is significantly related to feeling useful. Moreover, it appears that subjective usefulness could also provide a resource of energy or vitality for all physical, psychological, and social activities, and it could reinforce the desire to help others through volunteering. Nakanishi and colleagues (1998) reported that the sense of "life worth living" (ikigai) is reflective of an active physiological and psychological profile. However, no studies have compared the impact of subjective usefulness and engagement in helping others on the rate of mortality. We found that the odds ratio for subjective usefulness was higher than that for engaging in social roles as the index of helping others. Our finding strongly suggests that subjective usefulness may be more beneficial to long-term survival among older adults than social benefits such as volunteering.
Some limitations of this study should be noted. First, all the information was obtained by one-on-one interviews. It is well known that respondents tend to give "socially desirable" answers to interview-administered questionnaires, compared with self-administered questionnaires (Okamoto et al., 2002; Siemietycki, 1979). In addition, systematic errors may also be present because some respondents probably overreported or underreported their subjective usefulness. Accordingly, it is quite likely that "socially desirable" answers may also have partly influenced our results. Second, subjective usefulness appears to lead to improved behavioral patterns and enhanced general health status, thus helping older persons function more effectively both at home and in society. However, an inverse relationship between subjective usefulness and mortality remained even after adjustments for the degree of self-rated health and other confounding variables. In addition, we used information collected at baseline to predict mortality up to 6 years later. Subjective usefulness may have changed during follow-up periods. However, in the present study, we observed that the level of subjective usefulness was virtually stable over 6 years among surviving older adult participants (Spearman correlation coefficient, r =.94; = 0.92).
Taking previous studies into account, our findings suggest that the beneficial effect of the feeling of usefulness on longevity would be generalizible to countries other than Japan. When older Japanese adults describe their own usefulness or importance, they often use the following statement: "Things don't proceed if I am not here." This suggests that the source of the feeling of usefulness is having a strong sense of being at the center of the world.
In conclusion, the findings of the present study suggest that subjective usefulness is likely to have the beneficial effects of enhancing or promoting better health status and well-being in later life and reducing mortality. However, little is known about the relationship between subjective usefulness and mortality through changes in self-rated health among older adults. Further longitudinal studies are needed to better understand whether and how subjective health is related to person-specific changes in self-rated health, and subsequently to mortality in older adults.
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Footnotes |
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Received for publication June 6, 2003. Accepted for publication March 15, 2004.
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This article has been cited by other articles:
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  T. L. Gruenewald, A. S. Karlamangla, G. A. Greendale, B. H. Singer, and T. E. Seeman Feelings of Usefulness to Others, Disability, and Mortality in Older Adults: The MacArthur Study of Successful Aging J. Gerontol. B. Psychol. Sci. Soc. Sci., January 1, 2007; 62(1): P28 - P37. [Abstract] [Full Text] [PDF]
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