Introduction

Regardless of country, it is important that studies concerning longevity should focus on the social factors of the longevity index (LI), as health ageing is typically associated with such factors. This retrospective analysis of the social factors that contribute to the LI may help to identify the factors associated with healthy ageing. Therefore, the prevalence rate of centenarians among the total population of a country could be affected by its social factors, such as health expenditure, occupational injuries, suicide and dependency expenditure.

Previous studies have focused on centenarians to estimate the genetic factors resulting in the longevity clustered in particular families (Sebastiani et al. 2012; Terry et al. 2004). Further, since social networks predict longevity across societies, the studies have isolated social factors in this regard—including lifestyle, and social economic relationships (Rajpathak et al. 2011; Sauvaget et al. 2011). Longevity is especially considered to reflect the combined influence of environment factors, lifestyle choices, and genetic factors. Healthy aging is thought to reflect the combined influence of environmental factors and genetic factors (Sebastiani et al. 2011). Therefore, this means that environment factors of longevity can be attributed to social factors of healthy aging.

The LI of centenarians may represent the most ideal examples in healthy ageing. Here, healthy aging does not only indicate people who have lived for 100 years or longer; it means that the concerned centenarians also possess good functional capacity and general well-being (Ozaki et al. 2007). Even though healthy aging is a multidimensional construct having both objective and subjective dimensions, healthy aging invariably includes absence of disease and disease-related disability and active engagement with life (Pruchno et al. 2010).

The primary aim of this study was to estimate the LI as prevalence rate of the centenarians among the total population residing in 18 OECD countries. The secondary aim was to clarify the correlation between LI and the social factors of healthy ageing by using a regression model.

Methods

Hypothesis of Social Factors of Healthy Ageing

In this paper, a conceptual study of social factors was carried out within the framework of approaches obtained from the results of previous studies. Health ageing in centenarians indicates the physical state of living for hundred years with an absence of disease, the mental state characterised by the preservation of functional capacity, and social well-being attested to through an active life and participation in society (Cameron 2012; Rowe and Kahn 1987).

Therefore, the components of the social factors of healthy ageing included in this study can be hypothesized as follows: (1) [Hundred]: physical existence for one hundred years with an absence of disease (2) [Help]: a level of mental health that aids sound cognitive functioning in the elderly, and (3) [Active]: a life marked by active social engagement. We proposed the hypothesis that the following are the social factors meriting consideration: depicts the framework of the social factors as healthy ageing, proposed in this paper: (1) [Hundred]: with prevention of occupational injuries (OI), (2) [Help]: with enhancement of the dependency ratio through dependency expenditure (OR), (3) [Active 1]: with enhancement of the health expenditure capacity of the gross domestic product (HGDP), (4) [Active 2]: with enhancement of the public expenditure on health (PH), and (5) [Active 3]: with the prevention of suicide ratio by both genders (SR) (6) [Active 4]: with the prevention of suicide ratio by women (SRW).

This factors variable was selected because raising the health expenditure can directly improve the health status and reduce health inequity through the financing provision of public goods. The influence of the above factor on life expectancy and health expenditure is significant (Berkman 2009; Swift 2011). On the other hand, Labour factors included the factor of occupational injuries. Since occupational injuries pose the greatest risk of death, they are barriers to health care. Younger workers are especially representative of the U.S. labour force and face a high risk of injury while on the job. Employers need to ensure that their workers have the requisite training and personal protective equipment to perform their jobs safely (CDC 2010). A recent study has identified a significant and independent positive correlation between the elderly dependency ratios and general population suicide rates of both genders (Shah 2011; Yamauchi et al. 2012). In particular, suicide is apparent in women of postmenopausal age (Ling et al. 2011). Therefore, a recent study proposed that based on the empirical estimates, healthy ageing is expected to reduce the impact of increased life expectancy on real health expenditure (Bjørner and Arnberg 2012).

Design of Model of Selected Social Health Factors

This study examined the influence and association between the LI of centenarians and the social factors prevalent therein. A linear regression model was used to estimate the ratio of the LI in terms of the different factors. Thus, depending on the variables selected, the regression model yielded the following results. The two models of healthy ageing formulated in this study included the following as variables: Of the two proposed models, models 1 assigned more significance to HGDP, PH, OI, and SR as the best predictors of the LI. However, Model 2, which was based on Model 1, included DR, and was perhaps the best model. Based on this model, we derived the following hypothesis Increases in HGDP, PH, and DR, will lead to a corresponding increase in the LI in the 18 OECD countries. However, decreases in OI, SR, and SRW will result in a corresponding increase in the LI.

The LI of Centenarians

The objective was to identify the differences in the social factors included in the LI in OECD member countries. This study utilized the demographic databases of centenarians from the above countries to calculate the following parameters (Formula 1): the proportion between the centenarians and the total population, the areas in which the centenarians live, and the gender distribution among centenarians.

$$ \mathrm{Longevity}\;\mathrm{index}\left( {\mathrm{LI}} \right)=\left[ {{{\mathrm{Centenarians}} \left/ {{\mathrm{Total}\;\mathrm{Population}}} \right.}} \right]\times 100,000 $$
(1)

These LI used the official data of the OECD member countries and were calculated on the basis of their census documents.

Selected OECD Member Countries

The data for conducting international comparisons of the number of centenarians in the OECD member countries was obtained from the 2000–2010 Census Data of the National Statistical Offices of all the OECD member countries. We excluded those OECD member countries from the LI analyses of centenarians for which the data for the total population and the number of centenarians was insufficient. Finally, 18 OECD member countries were selected for this study.

Data Regarding Centenarians

The data for the analysis of centenarians in the selected member OECD countries were obtained from the population censuses conducted by the National Statistical Offices of 18 OECD countries (Table 1).

Data of Social Factors

Social indicators from OECD member countries were included: these were taken from Dataset (OECD 2009), and Korean Statistical Information Service (KOSIS 2010) and The World Bank (2010). The following indicators were used: HGDP in 2005; PH, a percentage in 2005; DR, a percentage of those aged 0–14 years and 65 years and above in 2005; SR, per 100,000 people in 2004; SRW, per 100,000 people in 2004.

Results

LI in the Selected OECD Countries

Compares the LI of the centenarians in the selected OECD member countries. The results regarding the longevity of the ageing populace indicated that among the OECD countries, France (LI: 36) scored the highest on the LI. The 18 OECD countries included the Japan (LI: 20), United States (LI: 18), Italy (LI: 17), the United Kingdom (LI: 17), Australia (LI: 16), Canada (LI: 15), New Zealand (LI: 13), Denmark (LI: 13), Iceland (LI: 12), Netherlands (LI:8), and Ireland (LI: 7). Korea (LI: 2) scored the lowest on the LI; approximately 18 times lesser than France (Table 1).

Table 1 Prevalent of LI in selected OECD countries
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Model of Prediction Variables for LI

In order to investigate the direct relationships between the social variables as healthy ageing and longevity in the selected OECD member countries, we conducted a multiple regression analysis. Tables 2 and 3 show the analysis of the social factors for the LI in the 18 OECD countries. Although significant positive correlations were found between the LI of centenarians and social factors such as HGDP, PH and DR, negative correlations were found between the LI of centenarians and social factors such as SR, SRW, and OI. Finally, the LI predictors were used to form a model of healthy ageing, with higher HGDP as health expenditure, and higher DR as dependency expenditure, and lower SRW as risk of life, including lower OI as labor injuries (R 2 = 0.909, P = 0.023).

Table 2 Correlations of social factors as healthy ageing for LI
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Table 3 Model of prediction variables of social factors for LI
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Discussion

Significance of LI as Healthy Ageing

We investigated the social factors associated with the LI. The present LI, which is based on a study of the centenarians and features in the national censuses of the selected 18 OECD countries, found that, on an average, centenarians accounted for 14 per 100,000 of total the population. In this study, such an LI of centenarians was considered to be a model for social factors as healthy ageing.

Higher Health Expenditure

HGDP was included in almost all the models featured in this study. An increase in HGDP and PH leads to an increase in the LI predictors of health where in the elderly live actively engaged lives, since HGDP and PH are contributory factors to the longevity predictor of health. The HGDP has a significant influence on the life expectancy in most countries (Swift 2011; Malley et al. 2011). The findings of this study suggest that a higher as positive correlations PH (r = 0.686, p = 0.002) and HGDP (r = 0.479, p = 0.044) may be important contributors to the longevity predictor of independence.

Lower Rates of Suicide in Both Genders

A reduction of SR and SRW were also significantly associated with the longevity of risk of life as healthy ageing. A decrease in SR and SRW leads to an increase in the LI predictors of healthy ageing where in the elderly live actively engaged lives. A previous study conducted in some countries documented that an Australian suicide study found an overall decline in the male suicide rate from 1998 in suicide attempts (Page et al. 2006). Further, in Italy, the suicide rates for both men and women decreased from 1980 onwards (Vichi et al. 2010). Nevertheless, a study conducted in Korea has shown an unprecedented increase in suicides over the last decade (Kwon et al. 2009). Korea ranks at the top of the selected OECD members countries as regards suicide statistics. On the other hand, suicide rate identified statistically significant relationships in women 60 years or older which suicide is apparent in women of postmenopausal age (Ling et al. 2011). The most prominent increase in successful suicide attempts was observed among the elderly of both genders, while relative inequalities in suicide due to economic status widened over time (Kim et al. 2010). Therefore, the findings of this study suggest that negative correlations and SRW (r = −0.685, p = 0.006) and SR (r = −0.692, p = 0.005) may be important contributors to the longevity predictor of independence. Although it was not possible to determine the causes of suicide, future research on healthy ageing should address this issue and focus on ways of preventing these. These governments of OECD led suicide prevention programs are most effective in preventing suicides among the elderly and young populations (Matsubayashi and Ueda 2011).

Higher Dependency Expenditure Ratio

DR was associated with the LI of centenarians determined in this study. An increase in DR leads to an increase in the LI predictors of health where in the elderly live actively engaged lives, since DR are contributory factors to the longevity predictor of healthy ageing. Although the impact of elderly dependency ratios may interact with the mediating cultural factors (Shah et al. 2008), however, in the current study of the DR in Korea, which involved investigating the lowest DR in the selected 18 OECD countries, in the LI of Korea predictors as healthy ageing were estimated to be the lowest. Therefore, the findings of this study suggest that a higher as positive correlations DR (r = 0.545, p = 0.024) may be important contributors to the longevity predictor of independence.

Reduction of Incidence of Occupational Injuries

The present study also showed that the incidence of OI was associated with the LI of centenarians. A decrease in OI leads to an increase in the LI predictors as healthy ageing. Occupation is associated with longevity (Kim 2002). The OI is particularly associated with fatal accidents. The mortality rate stemming from OI is a well-known public health concern. In the U.S., a high percentage of younger workers die from OI (CDC 2010). This means that workers who are vulnerable to the risk of OI may not have the same life expectancy as the centenarians. Therefore, the factor of OI appears to be a chief contributor of death. Therefore, the findings of this study suggest that a higher as negative correlations OI (r = −0.746, p = 0.008) may be important contributors to the longevity predictor of independence. Employers and public health organizations should seek to reduce the exposure of their employees and workers to the risks of OI by reducing injury hazards through the provision of safer workplaces.

Limitations

Despite the strengths of LI of centenarians based sample and the use of established methods to estimate the social factors, this study had limitations. Although LI are a perennial interest as healthy ageing, two limitations of the LI are changed age-specific fertility and the migration in populations.

Conclusion

In summary, the study of the LI of centenarians in 18 OECD countries has identified the following important aspects of healthy ageing: (1) reduction of incidence of OI in Labour Injuries; (2) higher DR in dependency expenditure; (3) higher HGDP and PH; and (4) alleviation of the causes of SR and SRW attempts. The findings imply that an aged society plays an important role in ensuring the continued longevity of older people; therefore, the governments of OECD countries must strengthen their preventive social programmers and increase their existing support services for the elderly through increased financing of the health sector.