The brain fog often experienced by people living with long COVID could stem from blood clots, new research has suggested.
While many who get a positive test for coronavirus recover within a few days, not everyone who overcomes the virus returns to a clean bill of health, with many thought to be suffering from ongoing impacts.
Those living with long Covid have reported a number of symptoms that can linger for weeks or even years.
Despite supposedly clearing the virus from their body, sufferers are thought to experience everything from fatigue to organ damage, but some people with the condition experience problems with blood flow and lung capacity, which have been linked to tiny, abnormal blood clots.
The research, published in the journal Nature Medicine, suggests blood clots could also drive the neurological symptoms of long Covid, such as brain fog, which can impact memory and the ability to focus and execute tasks.
However, the study authors weren't able to fully establish how the clots might actually damage nerves or the brain to trigger brain fog.
Lead study author Dr Maxine Taquet, a clinical psychiatrist at the University of Oxford, told Live Science that fibrinogen-related blood clots may be derailing blood flow to the brain or perhaps directly interacting with nerve cells.
Read more: Long Covid
Three types of long Covid each with different symptoms, researchers say (Sky News, 2-min read)
Long Covid patient opens up about his mental health (Yahoo Life UK, 1-min read)
Here's why you feel breathless when you have long Covid (Yahoo News UK, 2-min read)
How common is long Covid?
According to the World Health Organisation (WHO), the most recent studies show that around 10 to 20% of people who get Covid may go on to develop long Covid symptoms, and up to 17 million people across the WHO European Region experienced long Covid in 2020 and 2021.
A February 2023 report from the Office for National Statistics (ONS) found that an estimated two million people, or 3.1% of the British population, are experiencing self-reported long Covid symptoms as of 2 January 2023.
Robbie Williams could be one of the thousands currently living with long Covid, having cited the condition as the reason he stopped mid-concert earlier this year.
"No, stop stop," the Rock DJ singer said after performing his third song. "I’m f***ed. I’m f***ed. It’s long Covid, I’ve got long Covid. It’s not my f***ing age, you f***ers," he added before resuming his setlist.
What is long Covid?
While long Covid, or post COVID-19 syndrome, is a new condition that is still being studied, it is thought to be triggered by the COVID-19 infection.
WHO defines long Covid as the "continuation or development of new symptoms three months after the initial SARS-CoV-2 (COVID-19) infection, with these symptoms lasting for at least two months with no other explanation".
Long Covid causes
Anyone who experiences the virus is at risk of developing long Covid, but a 2023 study of 800,000 people by Harvard University found that those with pre-existing health conditions such as high blood pressure, chronic lung disease, obesity and diabetes were more likely to develop long Covid.
While the cause is still being studied, a small-scale study from the University of Utah recently pinpointed a particular set of proteins in the body that control growth and the activity of immune system cells that were "almost undetectable among individuals who had long Covid".
This caused researchers to suspect that, for some people who get COVID-19, their lungs and other organs are unable to fully heal which can leave them more susceptible to other illnesses.
Who is most likely to experience long Covid?
The ONS report found that long Covid is more common in:
people aged 35 to 69
people living in more deprived areas
social care workers
those with an activity-limiting health condition or disability
Long Covid symptoms
According to the NHS, the most common symptoms of long Covid are:
Fatigue (extreme tiredness)
Shortness of breath
Loss of smell
Other common long Covid symptoms include:
Brain fog (memory and concentration issues)
Chest pain and tightness
Insomnia and difficulty sleeping
Pins and needles
Anxiety and depression
Earaches and tinnitus (ringing of the ears)
Nausea, diarrhoea, stomach aches, loss of appetite
High temperature, cough, headaches, sore throat, changes to taste and smell
WHO says the most common symptoms of long Covid include “fatigue, shortness of breath and cognitive dysfunction”, and adds that the condition can have over 200 different symptoms.
An ONS report found that fatigue was the most commonly reported symptom for long Covid patients (71%), followed by difficulty concentrating (52%), shortness of breath (48%) and muscle aches (47%).
Watch: Long COVID smell loss 'linked to changes in the brain'
Long Covid treatment
If you suspect you have long Covid, you can speak to your GP about managing your symptoms and possible tests to rule out other things that could be causing them.
If your symptoms are having a big impact on your life, your GP may refer you to a specialist service that could help you recover.
A healthcare professional can refer you to the NHS’s Your COVID Recovery programme, an online recovery programme that can offer support and ways to manage symptoms.