Dutch researchers say persistent fatigue in patients with ‘long Covid’ has identifiable biological cause

Medical researchers in the Netherlands have established for the first time that persistent fatigue in patients with so-called long Covid has an identifiable biological cause, a finding with significant implications for the way the condition is treated.

Estimates suggest that long Covid – the name given to a diverse group of health problems often lingering after a Covid-19 infection – has affected up to 100,000 people in the Netherlands since the pandemic, and the government has set aside €32 million to fund research into its causes.

The latest findings from Amsterdam university medical centre (AMC) teaching hospital, published on Friday in the journal Nature Communications, show, essentially, that the muscle cells in patients with long Covid produce less energy than those of their healthy counterparts.

The results were based on tests in which 25 participants with long Covid and 21 without were asked to cycle for 15 minutes. Researchers examined their blood and muscle tissue one week before the test and one day after it and compared the two. What they saw was that the cycling prompted a long term worsening of the fatigue – and pain-related symptoms presented by those with long Covid – a distinctive condition now known as “post-exertional malaise” or PEM.

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“We saw various abnormalities in the muscle tissue of the patients”, said Rob Wust, assistant professor in human movement sciences. “At the cellular level we saw that the mitochondria of the muscle, often described as the energy factories of the cell, work less well and produce less energy.”

This led to the clear conclusion, said Prof Wust’s colleague, Michèle Van Vugt, professor of internal medicine at AMC, that the cause of the fatigue “really is biological” – rather than a feature of the psychological distress associated with Covid-19 or of “pandemic-related anxiety” in the population.

“The brain needs energy to think, and muscles need energy to move”, said Prof Van Vugt. “This discovery means we can now start to research an appropriate treatment for long Covid patients.”

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One of the theories about the condition is that coronavirus particles may remain in the bodies of those who have had the infection. However, Prof Van Vugt said, “we did not see any indication of this in the muscles”.

In addition the research also shows that the heart and lungs of the long Covid patients functioned well. “This means that the long-lasting debilitating effect on a patient’s fitness is not caused by abnormalities in the heart or lungs.”

Although the majority of those infected with the Covid-19 virus recover within weeks, about one-in eight will get long Covid, say the Amsterdam researchers.

The World Health Organisation says long Covid typically starts around three months after infection, but other studies suggest it can be much sooner at four or five weeks.

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