Healthcare in the United States is often touted as the best in the world, but Americans seem to be in worse health than their British peers, a new study shows.

Even the richest Americans in their 50s and early 60s had higher rates of diabetes, high blood pressure, arthritis and mental health problems than their wealthy British counterparts.

Those who were in the top 10% in earnings — after-tax median incomes of $144,000 for Americans and $71,000 for the English — had significantly worse health on four of 16 outcomes that were studied. Americans did not have better outcomes than English adults on any of the 16 health measures, even in the highest income group, the researchers noted.

Still, the biggest gaps in health were found among those who made the least money. Middle-aged Brits in the bottom 20% of income had better health than the poorest Americans.

Poor Americans were much more likely to have high blood pressure, arthritis, diabetes, heart problems, stroke, chronic lung disease and mental health problems than their poor British peers, the researchers found.

The Americans were also much more likely to have a high reading on three key health measurements — blood pressure, blood sugar and a marker for inflammation called C-reactive protein.

The disparities persisted even after adjusting for age, gender, race, household size, marital status, immigrant status and education level.

For the study, researchers from the University of Michigan and the University College London used data from two studies that included data on nearly 13,000 Americans and 5,700 Brits.

The team focused on the age group just below the main eligibility age for Medicare in the United States, so income can affect health care coverage, or lack thereof. By contrast, all Brits are automatically covered by the National Health Service. The age of 55 was the youngest age for which nationally representative data was available for both countries, the researchers noted.

"This approach lets us shed a lot more light on the within-country differences, as well as the differences between countries," said researcher HwaJung Choi, a health economist and research assistant professor of internal medicine at Michigan.

"If we looked at older adults, we likely wouldn't see this level of discrepancy, partly because of the effects of Medicare coverage," she said in a university news release.

Although Americans fared worse than their British counterparts, income still played a role in health care in the United Kingdom, with low-income Brits faring worse than their wealthier counterparts.

"These are remarkable results, and confirm the value of comparisons between countries," said study co-author Andrew Steptoe, head of the Research Department of Behavioural Science and Health at University College London. "Differences in health care are part of the story, but even in England where care is free for everyone at the point of delivery, there are still marked differences in health related to income."

The report was published online July 13 in the journal JAMA Internal Medicine.

"Our analysis provides a comprehensive view of health disparities across many key outcomes, and shines a brighter light on the large differences in health and risk for the rich and poor in our country," said co-author Dr. Kenneth Langa, a research professor of internal medicine at the University of Michigan.

"A number of the disparities that we found between low-income and high-income Americans — such as a higher risk of diabetes, hypertension and higher levels of inflammation — are likely contributing to the much higher risk for COVID-related complications and death among the poor," he added in the release.