Poorer countries obviously have less to spend on preventive medicine and health care than wealthier countries. That may explain why average longevity is much shorter in poor countries. To analyze this question, I examined the relationship between average life expectancy and income distribution in 1995, using a statistical technique called regression analysis. However, there is also a positive, statistically significant relationship between life expectancy and per capita income, leading to a predicted 6.3-year difference between the highest and lowest per capita GDP countries in the sample, based on income alone. When the two affects are considered simultaneously, differences among countries in life expectancy are fully explained by differences in standards of living.
Inequality of income is statistically insignificant.
However, government affects the distribution of income through taxation, which is often progressive, and through government expenditures, which may also favor lower-income individuals over those with higher incomes. A proper measure of income distribution would subtract all taxes from market income and add back direct and indirect government spending. Presumably, one of the functions of government is to improve the quality of its citizens' lives, and the length of one's life would seem to be paramount. The evidence suggests that the level of national income is important to longevity but that how it is distributed among the population does not matter, at least in high-income countries. Government, no matter how large it gets or how much it engages in income redistribution, does not appear to contribute to longevity in developed countries.