I am very lucky to live in the centre of London, one of the richest cities on Earth. Yet some people living in Westminster can expect to live 20 years less than others. ¡°In fact, if you catch the Jubilee tube line, for each stop east from Parliament, life expectancy drops by one year,¡± writes epidemiologist Michael Marmot in The Health Gap. But this remarkable fact tells only part of the story, because those with shortened lives can also expect to be plagued by more ill health.

What changes stop-by-stop on the eastward journey on the Jubilee line is the quality of people¡¯s lives. Housing becomes poorer, educational opportunities shrink and streets are more polluted and crime-ridden. All these factors conspire to give people less control over their lives. And lack of control is key, says Marmot. He knows this, bizarrely, because of his study of the Civil Service, an extreme example of a stratified organisation. In the Civil Service, decreasing rank is a perfect indicator of lower life expectancy and greater ill health.

Marmot, born in the UK but raised in Australia, has amassed a dizzying array of evidence on the ¡°social determinants of health¡±, making his book hard for all but the most wilfully ignorant policymakers to ignore. He begins with a graph that shows a steep increase in average life expectancy with a country¡¯s average income up to a threshold of $10,000 (?6,600), then no improvement with increasing income. Below $10,000, people are in absolute poverty, without adequate water, shelter and food. Once these necessities are attained, however, something else blights people¡¯s lives. Edwina Currie and others are being disingenuous in claiming there is no such thing as poverty in Britain. There is no absolute poverty, or very little, but this is irrelevant in a Western country where lack of control, born of inequality of opportunity, creates misery and truncates lives.

This is preventable, insists Marmot. But it requires the political will to act on evidence rather than prejudice, and divert resources to improving housing, educational opportunities, and, particularly, the experiences of children, whose brain development is inhibited by the stress hormone cortisol. Unfortunately, the British government is increasing inequality. Austerity, implemented to reduce UK debt, has not only doubled that debt but also diverted resources from poor to rich, who have doubled their wealth since 2008.

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The evidence, as this excellent book shows, does not support the assertion that the poor are to blame for being poor. As Doris Lessing said: ¡°Any human anywhere will blossom in a hundred unexpected talents and capacities simply by being given the opportunity to do so.¡±

Marmot believes that we should all want to improve things simply to give people longer and better lives, and he is reluctant to make an economic case. But the moral and economic cases reinforce each other: if we reduce inequality, we exploit a larger pool of talent, enabling more people to participate in the economy. Everyone, from bottom to top, benefits.

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There is, Marmot stresses, a ¡°health gradient¡±. So all of us have a shorter life expectancy than those at the top, not just the poor. All of us are affected by inequality. In the words of John Donne: ¡°Never send to know for whom the bell tolls; it tolls for thee.¡±

Marcus Chown, formerly a radio astronomer at the California Institute of Technology, is author of What a Wonderful World: Life, the Universe and Everything in a Nutshell (2014).

The Health Gap: The Challenge of an Unequal World
By Michael Marmot
Bloomsbury, 400pp, ?20.00
ISBN 9781408857991
Published 10 September 2015