Thomas Perlmann, far right, Secretary-General of the Nobel Committee announces the 2019 Nobel laureates in Physiology or Medicine during a news conference in Stockholm, Sweden. Picture: Pontus Lundahl/TT via AP

Stockholm - The 2019 Nobel Prize in Medicine has been jointly awarded to US-born scientists William Kaelin and Gregg Semenza and British scientist Peter Ratcliffe for their work on cells' use of oxygen, Sweden's Karolinska Institute announced on Monday.

Their research, the institute said, "paved the way for promising new strategies to fight anaemia, cancer and many other diseases."

Their work on how cells sense and adapt to oxygen availability shone light on what the Nobel prize-awarding committee called one of life's "most essential adaptive processes."

Prize committee member Patrik Ernfors told a news conference that the discovery highlighted "a system that is required for [the] body to function normally."

"Oxygen levels vary in different parts of the body, in tissues and organs, and in particular for example during exercise," he said.

It is a "dual" system that allows the cells to cope during low oxygen levels and also "generates an opportunity for the cells to regain normal oxygen levels," Ernfors added.

"This is such a basal physiological mechanism that allows us to colonize the Earth at different altitudes because oxygen levels vary at different altitudes," he said.

Professor Randall Johnson of the Nobel Committee, right, speaks during a news conference in Stockholm, Sweden. Picture: Pontus Lundahl/TT via AP

The system was also important in relation to diseases such as "anaemia, or cancer or heart attack or stroke or other disorders where you have a reduction in blood supply and oxygen," Ernfors added. 

Nobel Prize organizers managed to contact all three winners of this year's medicine prize, Thomas Perlmann, the secretary of the Nobel Committee, said.

They were "happy to share the prize with each other in this trio," he said.

By tradition, the prize-givers contact the winners by telephone to inform them just before making the public announcement.

Perlmann said US scientist William Kaelin - professor at the Harvard Medical School - had been the most difficult to get hold of. He had initially managed to reach Kaelin's sister, who gave him two phone numbers. The first appeared to be a wrong number, but the second led to Kaelin, who was "really happy, almost speechless" about winning the award, Perlmann said.

The Nobel Prize website posted a photo of Ratcliffe at his desk on its Twitter feed, shortly after the announcement, with the caption: "Grant proposal deadlines wait for no-one!"

Ratcliffe is director of the Target Discovery Institute at the University of Oxford, and Clinical Research Director, at the Francis Crick Institute.

Semenza is professor of medicine at the Johns Hopkins University.

The trio in 2016 won the Laskar Prize, another distinguished award. 

Laureates in the fields of physics, chemistry, literature and peace are also due to be announced in the coming week, followed by economics next week.

With the exception of economics, the prizes were endowed by Swedish industrialist Alfred Nobel (1833-96), the inventor of dynamite.

This year, each prize is worth 9 million kronor (908,000 dollars).

The Nobel Prize in Physiology or Medicine was first awarded in 1901.

Last year, two immunologists, James P Allison of the United States and Tasuku Honjo of Japan, were jointly awarded for their work on new therapies to combat cancer.

In line with tradition, the actual awards are presented on December 10, the anniversary of Nobel's death.

dpa