Americans have significantly higher rates of diabetes, heart disease, stroke, lung disease and cancer than English people in the 55 to 64 age group.

Sir Michael Marmot, professor of epidemiology at University College London, who led the British arm of the study, said the findings would surprise international health policy experts. His US colleague, James Smith of the Rand Corporation in California, added: “You don’t expect the health of middle-aged people in these two countries to be too different, but we found that the English are a lot healthier than the Americans.”

The researchers who were funded by several US and UK government agencies, set out to look at the social and economic factors affecting health but shifted emphasis when large differences emerged between the two countries. The study looked both at the way people reported their own health and – to guard against any bias from self-reporting – at objective biological markers of disease from blood tests. Altogether there were about 15,000 participants.

Samples in both countries were limited to whites and excluded recent immigrants, so as to control for racial and ethnic factors.

“This study challenges the theory that the greater heterogeneity of the US population is the major reason the US is behind other industrialised nations in some important health measures,” said Richard Suzman, programme director at the US National Institute on Ageing, which co-funded the research.

As expected, people with higher socio-economic status, as measured by their income and education levels, tended to enjoy better health. But because the national differences were so great, those at the top of the education and income scale in the US suffered diabetes and heart disease at a similar rate to those at the bottom of the scale in England.

The researchers are struggling to explain their findings. Their analysis shows that lifestyle factors – particularly the fact that Americans are more obese and take less exercise – cannot account for the whole discrepancy. though they may provide a partial explanation.

Different health systems may also be part of the story. The researchers note that the US spends $5,274 per head on medical care while the UK spends $2,164, adjusted for purchasing power. But Britain’s National Health Service provides publicly funded medicine for everyone, while Americans under the age of 65 have to rely on private insurance.

Prof Marmot suggested that, while the healthcare provided by the British state health service was not superior to the private US system, it provided important psychological reassurance.

As the researchers say in the journal paper: “To a much greater extent England has set up programmes whose goal is to isolate individuals from the economic consequences of poor health in terms of their medical expenditure and especially earnings and wealth reduction.”