This study looks at hundreds of theories to consider how income influences health. There is a graded association between money and health – increased income equates to better health. But the reasons are debated. Researchers have reviewed theories from 272 wide-ranging papers, most of which examined the complex interactions between people’s income and their health throughout their lives. Key points This research identifies four main ways money affects people’s wellbeing: Material: Money buys goods and services that improve health. The more money families have, the better the goods they can buy. Psychosocial: Managing on a low income is stressful. Comparing oneself to others and feeling at the bottom of the social ladder can be distressing, which can lead to biochemical changes in the body, eventually causing ill health. Behavioural: For various reasons, people on low incomes are more likely to adopt unhealthy behaviours – smoking and drinking, for example – while those on higher incomes are more able to afford healthier lifestyles. Reverse causation (poor health leads to low income): Health may affect income by preventing people from taking paid employment. Childhood health may also affect educational outcomes, limiting job opportunities and potential earnings.