Diminishing marginal returns and sufficiency in health-care resource use: an exploratory analysis of outcomes, expenditure, and emissions.

Background: Increasing health expenditure in low-income countries is associated with rapid gains in health status. Less attention has been paid to the possibility of diminishing marginal returns to health expenditure at high levels of spending, or to the relationship between health-care greenhouse gas emissions and outcomes. Our study aimed to investigate the existence, scale, and implications of diminishing marginal returns to health-care expenditure and emissions.

Methods: Segmented (piecewise) regression analysis was used to explore the relationship between two measures of health outcome from the Global Burden of Disease project (mortality amenable to health care [MAH] and health-adjusted life expectancy [HALE]), four aggregates of health expenditure per capita from the WHO Global Health Expenditure Database, and health-care sector greenhouse gas emissions per capita derived from a 2020 study by Lenzen and colleagues. Turning point knots-points at which the elasticity or velocity of increasing returns to expenditure and emissions changed substantially-were estimated and countries in the vicinity of these knots identified.

Findings: Rapidly increasing returns (improvements in population health as measured by MAH and HALE) to health expenditure were estimated in low-income and lower-middle-income countries; at levels of spending above approximately US$500 per capita, these returns start to slow. At levels of spending above those seen in high-income countries such as Italy (approximately US$3400), there is little or no evidence of further health returns to additional spending or to increasing health-care greenhouse gas emissions.

Interpretation: Dramatic improvements in population health outcomes could be achieved by additional investment in health expenditure in low-income countries. Conversely, continuing growth in health expenditure in high-income countries will, by itself, be unlikely to yield rapid improvements in health outcomes. Our findings inform the emerging debate on the importance of sufficiency within planetary boundaries-low-income countries need rapid growth in health expenditure, whereas high-income countries could potentially achieve better health outcomes at substantially lower levels of resource use.

Funding: None.