Beyond spending: nonlinear impacts of health financing and out-of-pocket costs on mortality in Africa

Existing evidence suggests that mortality remains disproportionately high across Africa, where gains in life expectancy continue to lag behind global progress. While health financing is central to health-system performance, its relationship with mortality in African settings remains insufficiently characterized, particularly when public spending, household out-of-pocket (OOP) payments, governance conditions, and demographic pressures are considered jointly. Our objective was to use a non-linear regression method to evaluate how health financing structures are associated with mortality and whether the association depends on the mode of financing. We use generalized additive mixed models (GAMMs) to allow for potential non-linear relationships between crude mortality rates and public health expenditure, out-of-pocket payments, political stability, and age dependency across 51 African countries from 2002 to 2022 ( N = 1,071 country-year observations). A tensor-product interaction assessed whether financial protection modifies the effect of public health spending. Region-specific models were fitted for Central, East, West, Southern, and Northern Africa. Public health spending was associated with lower mortality across Africa, with the steepest reductions below approximately US$80 per capita and diminishing returns thereafter. Out-of-pocket (OOP) spending modified these returns: OOP burdens below 15% of total health expenditure strengthened the estimated mortality benefit of public investment by about 60%, whereas burdens above 40% substantially eroded it. Regionally, the spending–mortality association was strongest in Central, Eastern, and Western Africa, but weaker in Southern and Northern Africa, where age dependency and governance quality were more prominent predictors. The expenditure–OOP interaction was most pronounced in Eastern Africa (EDF = 9.45, F = 4.45, p < 0.001). The continent-wide model showed strong explanatory performance (adjusted R 2 = 92.8%; deviance explained = 93.4%; N = 1,009). Increasing public health spending alone is unlikely to maximize mortality gains in Africa. Its impact depends on financial protection: reducing household out-of-pocket costs through pooled financing should be accompanied by expanded public investment. In Southern and Northern Africa, policy emphasis should also shift toward governance efficiency and demographic pressures. Subregion-specific strategies are therefore essential.