People living in the sickest parts of the United States switched political allegiance “dramatically” to support Donald Trump in the 2016 presidential election, according to a new study.

The researchers said they found this trend across the country, particularly in states that changed from Democrat to Republican.

However, they said the reasons behind the link were unclear.

Healthcare was a major issue during the election with Mr Trump promising to repealed Barack Obama’s Affordable Care Act.

The current President’s policies have been linked to an increase in the number of Americans without health insurance of 24 million.

The researchers said healthy people in the sickest counties may have been responsible for the shift towards Mr Trump, but added that it was also possible that unhealthy people may have voted “against their self-interest”.

The Republicans’ attempts to repeal ‘Obamacare’ have so far failed with Senator John McCain voting against the proposed replacement on the grounds that it is unclear “how much it will cost, how it will effect insurance premiums, and how many people will be helped or hurt by it”.

But, despite this, the unhealthiest counties out of more than 3,000 examined in the study – representing about 95 per cent of the US – seemed to like what Mr Trump was saying.

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One of the researchers, Professor Jason Wasfy, of Harvard Medical School, said: “Across the country, we found that voters in counties with poor public health shifted dramatically towards the Republican candidate in 2016, compared with 2012, an effect that was particularly strong in states where the results changed Electoral College votes.

“Although we cannot determine causality from these results, the findings raise the possibility of a role for public health status in determining voting behaviour.”

Writing in the Plos One journal, the researcher said: “Since President Trump has advocated for the repeal of the Affordable Care Act, which has been projected to increase uninsurance by 24 million Americans, sicker populations shifting votes to the Republican candidate may represent voters voting against their self-interest.

“Addressing that possibility with these data is complex for several reasons. Ultimately, whether policies promoted by the winning candidate in 2016 will improve or worsen community health is not specifically addressable from these data.

“As an analysis of community health within counties, we cannot analyse the voting behaviour of the specific voters within counties, for example, who would lose health insurance because of potential repeal of the Affordable Care Act.

“The shift of counties may be attributable to healthier voters within those counties. The sicker individual voters themselves may not have shifted voting at all, or may have even shifted towards the Democratic candidate in 2016.”

In addition to a correlation between the public health of a county and the extent of its shift towards Mr Trump, counties where his support increased had higher proportions of white people (79 to 65 per cent) and rural people (63 to 21 per cent), and a lower average household income ($45,142 to $60,086).

They also had higher teenage birth rates (43 to 31 births per 1,000 female population), a higher age-adjusted mortality rate (401 to 301 deaths per 100,000 population), but lower rates of violent crime (239 to 312 offences per 100,000 population).

“Even after adjusting for factors such as race, income and education, public health seems to have an additional, independent association with this voting shift towards Trump,” Professor Wasfy said.

“It's critical to interpret our results as reflecting county-wide ecological associations, rather than individual voting behaviour.

“More than anything, I think these results demonstrate that health is a real issue that can affect people’s lives and their decisions.