US President Barack Obama's stepmother said that she owed her life to the NHS.
British doctors and nurses saved Kezia Obama when she suffered chronic kidney failure seven years ago.
But the 66-year-old, who lives in Bracknell, Berkshire, insisted she would never have been able to afford healthcare if she had been in America at the time.
Ms Obama told the News of the World: "It's very simple: I owe my life to the NHS.
"If it wasn't for the NHS I wouldn't have been alive to see our family's greatest moment - when Barack became President and was sworn into the White House."
The intervention came after Republicans branded the NHS "evil" and "Orwellian" amid a major row over Mr Obama's plans for US healthcare reform.
Ms Obama said she fell seriously ill during a summer visit to the UK seven years ago. "I suffered severe kidney failure and pancreatic problems so there was a very real chance I might not have made it," she said.
"I was very down at the time but luckily I was here in Britain, in what was then a foreign country to me, where the doctors, nurses and surgeons cared for me like I was their own child."
The widow, who attended President Obama's inauguration in January, turned to the NHS again five years ago when she needed two hip replacement operations.
"If I'd been asked to pay for my new hips, well, I wouldn't have been able to afford them," she said. "I would have without a doubt ended up confined to a wheelchair."
