According to the latest Bloomberg Best (and Worst), which ranks countries in all sorts of metrics and areas, the following the healthiest (and least healthiest) nations in the world.
This health index takes into account several factors, including rates of mortality, smoking, immunization, healthcare access, satisfaction with the medical system, and life expectancy, among others. A country’s score reflects both the political factors at work — public health policies, the healthcare system, insurance regulations, etc. — as well as sociocultural influences, such as diet, lifestyle, and attitudes towards risky activities like smoking or heavy drinking.
Thus, the countries that performed the best tended to share similar characteristics: first and foremost, social, political, and economic stability (e.g., no war, mass unemployment, famine conditions, etc.); an efficient, cost-effective, and well managed universal healthcare system; good public infrastructure that promotes daily activity (parks, bicycle paths, walkable city plans, etc.); and a health-conscious culture values things like small food portions, outdoor recreation, or free time from work.
As per Jared Diamond’s work, geography and environment might play some role as well; most of the top performers were located in areas with generally stable and temperate climates, and thus far fewer diseases, erratic weather patterns, natural disasters, infectious diseases, and other detriments to individual and public health. (Singapore, which is located in a tropical region, is somewhat of an exception, but as an extremely well governed city-state, it has had an easier time minimizing or addressing the challenges poised by its climate.)