In 2008 a WHO commission reported a startling comparison. In Calton, a deprived area in the east end of Glasgow, men's life expectancy was about 54 years. In Lenzie, a more affluent area only a few miles away, it was about 82. A gap of nearly three decades separated people who lived a short drive apart and used the same national health service. The commission, chaired by the British epidemiologist Michael Marmot, summed up its findings in a sentence that became famous: "Social injustice is killing people on a grand scale."
The Whitehall studies
Marmot's own research began with British civil servants. The Whitehall studies, starting in 1967, followed thousands of government employees in London. None were destitute; all had steady office jobs and access to the National Health Service. Yet death rates followed job grades like a staircase. Men in the lowest grades, such as messengers and doorkeepers, had death rates roughly three times those of men in the top administrative grades during the early years of follow-up. Every step down the ladder brought worse health, not only the step at the bottom. Marmot called this the social gradient in health. Smoking, diet and blood pressure explained only part of it. Much of the rest seemed linked to how much control people had over their work and lives, and to the chronic stress of low status.
Social determinants of health
Public health researchers use the phrase social determinants of health for the conditions in which people are born, grow, live, work and age. They include income, education, housing, neighborhood safety, working conditions, access to healthy food and to medical care, and discrimination. Medical care matters, but it is only one piece. A child growing up in a damp, moldy apartment beside a highway is more likely to develop asthma no matter how good the local clinic is. Education is one of the strongest predictors of health: in many countries, adults with university degrees live years longer than those who did not finish high school.
Race, place and history
Health gaps often follow lines drawn by history. In the United States, Black women die from causes related to pregnancy at roughly three times the rate of white women, and the gap persists even among women with college degrees. Neighborhoods that were "redlined" in the 1930s, marked as risky for mortgage lending largely because of the race of their residents, still tend to have fewer trees, hotter summers and higher rates of some illnesses, such as asthma. Indigenous peoples in many countries, including Australia, Canada and the United States, have shorter life expectancies than their national averages, a pattern tied to dispossession, poverty and underfunded services. These are not mainly differences in biology. They are differences in circumstance, many of them created by policy and therefore open to change by policy.
The inverse care law
In 1971 the Welsh family doctor Julian Tudor Hart described what he called the inverse care law: the availability of good medical care tends to vary inversely with the need for it. Poorer areas, which have more illness, often have fewer doctors, longer waits and older facilities. The same pattern appears in screening, dental care and mental health services. In response, many public health programs follow proportionate universalism, a principle from Marmot's later work: services available to everyone, but with more effort and resources directed to those with the greatest need.
Measuring and closing gaps
You cannot fix what you do not measure. Health agencies increasingly break down their data by income, race, neighborhood, disability and other factors, because averages can hide large inequalities. Interventions that address root causes include early childhood programs, paid sick leave, better housing standards, community health workers drawn from the neighborhoods they serve, and clinics that are easier to reach by bus or open in the evening. This level focuses on gaps within societies, which exist even in the richest nations.
Worked example: two zip codes
A county finds that children in one zip code visit the emergency room for asthma five times as often as children in another just across town. A narrow response would hand out more inhalers. A public health response asks why. Investigators find that the first area has older rental housing with mold and cockroaches, both asthma triggers, sits beside a freight route with heavy diesel traffic, and has a single pediatric clinic with a long waiting list. So the county works on several levels at once: enforcing housing codes and funding repairs, sending community health workers to visit families and remove triggers at home, rerouting trucks or planting tree buffers, and adding evening clinic hours. Then it tracks emergency visits by neighborhood. The goal is not equal averages on paper, but children who can breathe.