Chronic fatigue is not in your head, it's in your blood - experts

People with ME - or chronic fatigue syndrome - have major differences in their blood compared with healthy individuals, experts are suggesting.

University of Edinburgh researchers said their findings could pave the way for a "game-changer" diagnostic test.

Prof Chris Ponting said: "For so long people with ME/CFS have been told it's all in their head. It's not. We see it in their blood."

However some critics of the study said researchers had "overstated" the significance of their work.

The study used data from the UK Biobank – a health database of over half a million people – to compare 1,455 ME/CFS patients with 131,000 healthy individuals.

The research showed the results were mostly unaffected by activity levels.

The university team said the volume and consistency of the blood differences support their long-term goal of developing a diagnostic blood test.

Researcher Dr Sjoerd Beentjes told BBC Radio's Good Morning Scotland: "One thing that our evidence points at is that ME is very much a condition in the blood.

"Perhaps previously held perspectives are not quite the case.

"It is really not due to inactivity and we hope that this helps with problems where individuals are disbelieved of their symptoms."

What are the symptoms of ME?

ME stands for myalgic encephalomyelitis and is also known as chronic fatigue syndrome (CFS).

The largest ever biological study of ME/CFS - which is estimated to affect 50,000 people in Scotland - identified consistent blood differences associated with chronic inflammation, insulin resistance, and liver disease.

The main feature of the condition is post-exertional malaise (PEM) - a delayed and dramatic worsening of fatigue that comes after minor physical effort.

Other symptoms include pain, brain fog and tiredness that does not improve with rest. Causes are unknown and there is currently no diagnostic test or cure.

Dr Beentjes also said ME was a "female bias" condition with the ratio of patients estimated to be 3:1.

Some experts have criticised the University of Edinburgh research

The Edinburgh researchers examined more than 3,000 blood-based biomarkers and accounted for differences in age, sex, and activity levels.

The results were replicated afterwards using data from the US

Prof Chris Ponting, of the university's MRC human genetics unit, said: "For so long people with ME/CFS have been told it's all in their head.

"It's not. We see people's ME/CFS in their blood.

He said the evidence should "dispel any lingering perception that ME/CFS is caused by deconditioning and exercise intolerance".

However, some experts have criticised the study.

Alan Carson, professor in neuropsychiatry at the University of Edinburgh, said the researchers overstated the significance of their work.

Prof Carson said: "If one wants to ask is ME/CFS a figment of the imagination, then this study shows it is not.

"However, to claim blood biomarker differences prove that a condition is 'not all in your head' fails to appreciate that both physical and mental illness can show similar types of results."

Kevin McConway, emeritus professor of applied statistics at the Open University, said: "I think this is an important piece of research, but it's also important to be careful not to claim too much from its findings.

"There's a lot more to do."