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Joe Herbert M.B, Ph.D.
Joe Herbert M.B, Ph.D.

The Scandal of Inequality and Its Effect on Mental Health

Financial inequality seems to be a major risk for mental illness.

The USA and the UK share many features. One is a language. Another is that they are both among the richest nations on earth. They also share a darker side: both are highly unequal societies. The USA is more unequal than any European nation, and the UK is the most unequal nation in Europe. Worse: this is growing larger as, it must be said, it is in many other Western nations. In the USA, the richest 1 percent have seen their incomes increase by around 200 percent since 1980, and there has been a particularly sharp increase since 2000, whereas for the bottom 20 percent it’s 40 percent, with only about 20 percent since 2000. The top 1 percent now has about a fifth of the total income: an average salary of around $6.7 million. For the bottom 90 percent, it’s $34,000. The UK is not much better. After a period of relative equality in the post-war years, the top 10 percent now earn 45 percent of the total income, and the bottom 50 percent about 8 percent. There’s a measure (Gini index) of national economic inequality: the higher, the more unequal. In 2016, the USA scored 41.5, and the UK 35.2. There are more unequal countries: South Africa scored 63.0 and Brazil 51.3. At the other end, we find (not surprisingly) the Scandinavian countries: Denmark 28.2, Sweden 29.2.

Since the citizens of both the USA and the UK like to think of themselves as living in a civilized, sophisticated and caring community, there is a point at which inequality becomes morally and ethically unacceptable. That point is highly sensitive to the prevailing social and cultural environment. Victorian Britain, in which inequality was even higher than it is today, was little concerned about the public and plentiful display of extreme poverty, though a few individuals swam against this tide of indifference to found Poor Laws and workhouses (which were squalid by today's’ standards). Nowadays we like to think of ourselves as more concerned: hence official, governmental, help with food and money to the poorest in both countries. The rich, to an extent, pay taxes which help the poor. Yet inequality keeps rising. There are street sleepers in both countries.

But there’s more to it than moral disgust. Every study on the health of a country shows that one of the strongest prediction of longevity, good health, and quality of life is socio-economic status (SES): how rich or poor you are. Interestingly, this is the same in the UK, which has a universal high-quality health service that is free to all, as in the USA, which does not. So all the effect of poverty on health is not easily explained by access to health services. And there’s more. If we compare health across countries, there is one expected finding: all the measures of health are worse in poorer countries than richer ones. Not surprising. But here’s another finding that may surprise you: about half the difference between health in the top and bottom of the SES scale is not due to absolute levels of poverty but to the gap between the richest and poorest: in other words, the degree of inequality, not its level. Karl Marx, not everyone’s favorite politician, defined poverty as the unequal distribution of wealth (relative poverty). He had a point!

Inequality has a direct impact on mental health. Sweden, a rich country with an excellent and accessible health service, but low inequality, has much less social and mental health problems than the UK, with an equally good health service but much higher inequality. The USA has an even worse health score. Men seem particularly liable to mental disorders as their income declines. Depression is strongly associated with lower income and greater inequality, though this has only really been studied adequately in high-income countries.

What is the mechanism linking financial inequality to mental illness, particularly depression? Since we do not know the ‘cause’ of depression at either social, genetic or neurobiological levels, any suggestions must be speculative. Poverty is related to feelings of social defeat and inferiority, as well as social isolation, alienation, and loneliness. These are accentuated if poorer people live in a society that allows them to compare themselves to much richer ones. Robert Sapolsky, in a recent Scientific American article (well worth reading) suggests that relative poverty generates stress, and stress generates overactivity of the hormonal and neural responses to stress which include secretion of cortisol, the stress hormone. Lower SES is associated with greater levels of stress (sometimes called ‘allostatic load’). We know that higher cortisol is a risk factor for depression. Lower SES children and adults have higher cortisol levels than richer ones. Depression is not the only mental disorder associated with SES. As every scientist knows, association does not prove causation, but the gun is beginning to smoke.

There are other social risks for illness, first demonstrated by showing statistical correlations. Smoking is one, and the marked decrease in smokers has had a corresponding effect on lung cancer and heart disease. Obesity is the next social challenge, one that both the USA and UK are taking seriously. Now we should give economic inequality the same urgent attention. Not only is it a social and communal disgrace, but it also seems to contribute to the huge burden that mental illness puts on both USA and UK. And that’s without any consideration of the individual pain and disaster that mental illness represents for many of those experiencing it.


Patel et al (2018) Income inequality and depression: a systematic review and meta-analysis of the association and a scoping review of mechanisms. World Psychiatry, volume 17 pages 76-89

Gruenewald et al (2012) History of socioeconomic disadvantage and allostatic load in later life. Social Science and Medicine, volume 74 pages 75-83

Robert Sapolsky (2018) The science of inequality. Scientific American. November 2018

About the Author
Joe Herbert M.B, Ph.D.

Joe Herbert, Ph.D., is an emeritus professor of neuroscience at the University of Cambridge.