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Health-adjusted life expectancy (HALE) is a widely recognized metric that captures both mortality and non-fatal health outcomes. Over the past few decades, global HALE has increased substantially and is strongly correlated with the socio-demographic index (SDI) (1-2). However, apart from social development indicators, the impact of population dynamics is often overlooked in studies of factors influencing HALE. Fertility rate, as a crucial element, may have a complex effect on HALE among older adults. Despite HALE increasing globally, the relationship between fertility rate and HALE, particularly among older adults in countries at varying development levels, remains underexplored. Exploring these issues is vital for formulating policies to promote the health and longevity of older populations in the context of low fertility. Therefore, this study analyzed country-level panel data from 1995 to 2019 to examine the impact of fertility rate on HALE at age 65, adjusting for socioeconomic factors and considering different SDI country groupings.
A country-level panel database spanning 1995 to 2019 was constructed using indicators of HALE, total fertility rate (TFR), human resources for health (HRH), gross domestic product (GDP) per capita, and total health spending (THS) per GDP from GBD Results (3). Data from Our World in Data (4), including average years of schooling, population density, and the percentage of the population living in urban areas, were also incorporated. After addressing missing values, 191 of 204 countries and territories were included in the analytical sample, yielding 4,625 observations. The impact of TFR on HALE was estimated using generalized estimating equations (GEE) with Gaussian distributions, considering HALE as the dependent variable and controlling for time effects. In both univariate and multivariate analyses, the quadratic term of TFR was incorporated, as the fitting analysis based on the scatter plot indicated a nonlinear relationship between TFR and HALE (Figure 1). Among covariates, HRH, per capita GDP, THS per GDP, and population density were log-transformed to control for skewness.
Figure 1.Scatter plot of TFR and HALE at age 65 across 191 countries, 1995–2019.
Note: A quadratic smoothing method was applied to fit the scatter plot.
Abbreviation: TFR=total fertility rate; HALE=health-adjusted life expectancy.
Countries were ranked and divided equally into three groups based on their 1995 country-level SDI. SDI is a composite measure of development status, calculated as the geometric mean of three indices, each scaled from 0 to 1: total fertility rate among women younger than 25 years, mean years of education among individuals aged 15 years and older, and lag-distributed income per capita. SDI is highly correlated with health outcomes, with a score of 0 representing the lowest theoretical level of development relevant to health and a score of 1 representing the highest. Multivariate GEE models stratified by SDI groups were then estimated. Given that SDI development trends between 1995 and 2019 varied across countries, leading to SDI grouping changes for some countries during this period, the following analysis was conducted. The sample was re-examined, revealing SDI grouping changes in 23 countries during the study period, representing 12.04% of the total sample. The multivariable GEE model was then re-estimated using the 2019 SDI groupings; the main results were unchanged. All computations were performed using STATA 17.0 (StataCorp LLC, College Station, TX, USA).
The estimated results from the GEE models are presented in Table 1. In the univariable model, TFR and all other socioeconomic indicators were statistically significant predictors of HALE. Specifically, HALE tended to increase linearly with decreasing TFR, as the quadratic term for TFR was not statistically significant (TFR: β=−0.48, P<0.001; TFR squared: β=−0.01, P=0.102). Considering other variables, for every 10% increase in HRH density, per capita GDP, and THS per GDP, HALE increased by 0.16 years, 0.14 years, and 0.07 years, respectively. Additionally, a 5-year increase in average years of schooling was associated with a 1.5-year increase in HALE.
Variables Univariable model Multivariable model All All Low SDI† Middle SDI† High SDI† TFR −0.48* (−0.59, −0.36) −0.71* (−0.82, −0.60) 0.37* (0.20–0.53) −0.64* (−0.98, −0.30) −1.41* (−1.85, −0.98) TFR squared −0.01 (−0.02, 0) 0.05* (0.04, −0.06) −0.05* (−0.07, −0.04) 0.11* (0.06, 0.16) 0.57* (0.46, 0.67) Log HRH (workers per
10,000 population)1.61* (1.56, 1.66) 1.21* (1.08, 1.33) 1.16* (0.98, 1.33) 0.38 (−0.12, 0.65) 1.66* (1.50, 1.82) Log per capita GDP
(2021 PPP)1.39* (1.34, 1.44) 0.19* (0.10, 0.29) 0.64* (0.51, 0.76) 0.11 (−0.08, 0.29) 0.34* (0.21, 0.48) Log THS per GDP 0.67* (0.57, 0.76) −0.01 (−0.10, 0.07) −0.04 (−0.14, 0.06) 0.25 (−0.41, 0.09) 0.88* (0.74, 1.01) Average years of
schooling (years)0.30* (0.29, 0.31) 0.32* (0.30, 0.33) 0.25* (0.23, 0.27) 0.29* (0.26, 0.32) 0.23* (0.21, 0.26) Percentage of urban
population (%)0.08* (0.08, 0.08) 0 (0, 0.01) −0.01 (−0.01, 0) 0.02* (0.01, 0.03) 0.02* (0.01, 0.03) Log population density
(people per km2)1.97* (1.87, 2.06) 0.65* (0.54, 0.76) 0.43* (0.26, 0.60) 0.39* (0.17, 0.61) 1.35* (1.19, 1.51) Number of countries 191 191 63 64 64 Observations 4,625 4,625 1,527 1,548 1,550 Note: 95% confident intervals are bracketed below coefficient estimates.
Abbreviation: TFR=total fertility rate; HALE=health-adjusted life expectancy; SDI=socio-demographic index; HRH=human resources for health; GDP=gross domestic product; PPP=purchasing power parity; THS=total health spending.
*P<0.05.
† Low SDI countries: 0.08–0.69; Middle SDI countries: 0.42–0.81; High SDI countries: 0.60–0.93.Table 1. Correlation of TFR and social development indicators with HALE at age 65 across different SDI country groups, 1995–2019.
In the multivariable analyses, after controlling for confounding variables, a significant quadratic relationship was observed between TFR and HALE (TFR: β=−0.71, P<0.001; TFR squared: β=0.05, P<0.001). As shown in Figure 2A, as TFR decreased, HALE accelerated after maintaining stability, consistent with the overall trend described by the observed values (Figure 1). Moreover, when compared to the univariable models, the results revealed that the effect sizes for GDP per capita and THS per GDP decreased, while the estimated coefficient for HRH and education remained stable (log HRH: β=1.21, P<0.001; log per capita GDP: β=0.19, P<0.001; log THS per GDP: β=−0.01, P=0.746; average years of schooling: β=0.32, P<0.001).
Figure 2.Estimated trends of HALE at age 65 based on observed TFR across different SDI country groups, 1995–2019. (A) Total countries; (B) Low SDI countries; (C) Middle SDI countries; (D) High SDI countries.
Note: The numbers in red in each figure show the range of observed TFR values in each SDI country group, and the corresponding predicted HALE values are also marked using red curves.
Abbreviation: HALE=healthy-adjusted life expectancy; TFR=total fertility rate; SDI=socio-demographic index.
Stratified analyses by SDI groups revealed distinct correlations between TFR and HALE among older adults. In low-SDI countries, HALE increased with rising TFR up to 4. Beyond this threshold, further increases in TFR were associated with a decline in HALE (Figure 2B). Conversely, in the middle- and high-SDI countries, increasing TFR did not reduce HALE. A monotonically upward trend was even observed in high-SDI countries (Figure 2C and D).
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