White middle-aged Americans are less healthy than their English counterparts, research suggests.
Higher rates of obesity in the US could not explain the differences
Americans aged 55 to 64 are up to twice as likely to suffer from diabetes, lung cancer and high blood pressure as English people of the same age.
The healthiest Americans had similar disease rates to the least healthy English, the Journal of the American Medical Association study found.
The US-UK research found greater links between health and wealth in the US.
The joint team from University College London, the University of London and health research organisation Rand Corporation, chose two groups of comparable white people from large, long-term health surveys in the US and in England.
In total, the study examined data on around 8,000 people in the two countries.
Each group was divided into three socio-economic groups based on their education and income.
They then compared self-reports of chronic diseases such as diabetes, high blood pressure, heart disease, heart attacks, stroke and lung disease.
The American group reported significantly higher levels of disease than the English.
Rates of diabetes were twice as high among the US group as the English.
One of the study's authors, James Smith of Rand, said: "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."
Those on the lowest incomes in both countries reported most cases of all diseases, except for cancer, and those on the highest incomes the least.
But these health inequalities were more pronounced in the US than they were in England.
The researchers suggested the lack of social programmes in the US, which in the UK help protect those who are sick from loss of income and poverty, could partly help explain why there was a greater link between Americans' wealth and disease.
But the study also found that differences in disease rates between the two nations were not fully explained by lifestyle factors either.
Rates of smoking are similar in the US and England but alcohol consumption is higher in the UK.
Obesity is more common in the US and Americans tend to get less exercise, but even when the obesity factor was taken out, the differences persisted.
One of the researchers Professor Sir Michael Marmot, of the department of epidemiology and public health at University College London, said people would automatically presume the differences were caused by the variance in healthcare systems.
US healthcare is funded through an insurance system while England's NHS is funded by taxation and is free at the point of use.
But he pointed out that Americans spent almost double per head on health care than the English do, even though the system was organised in a different way.
He said: "There is more uneven distribution in the US and something like 15% of Americans have no health insurance and (there are) a bigger number who are under-insured."
But this could not fully explain the differences because the richest Americans with access to highest levels of healthcare still had rates of poor health comparable to the worst off in England.
"We cannot blame either bad lifestyle or inadequate medical care as the main culprits in these socio-economic differences in health.
"We should look for explanation to the circumstances in which people live and work.
"We have to take a much broader look at social determinants of health in both countries.
"We need to do further research to fill in the jigsaw pieces of the puzzle," he added.
A Department of Health spokeswoman acknowledged health inequalities in England of the kind revealed in the research and said the government was anxious to tackle them.
It aims to reduce health inequalities in life expectancy and infant mortality by 10% and improve health generally.
"Health trainers, targeted initially at the most deprived communities, are one of the many initiatives which will help narrow this gap by supporting people to make healthier choices in their daily lives," she added.