When Covid-19 first emerged, it was initially thought that – like other coronaviruses affecting humans – it mainly caused lung problems.
But as the outbreak progressed, case studies began to suggest that some of the most severe complications of the disease affected more than just the lungs. From reports of ‘sticky blood’ raising the risk of deep vein thrombosis, heart attack or stroke, to neurological effects, many complications seemed to be affecting the blood vessels.
In particular, these problems can be caused by the way that Covid-19 affects the lining of the blood vessels, called the endothelium. This layer of cells is not a solid barrier – it can allow or block certain substances from entering or leaving the bloodstream depending on conditions in the body. It also has a vital role in allowing our blood vessels to function normally.
A healthy, well-functioning endothelium helps to keep our blood vessels relaxed and open to the flow of blood. It also releases substances that help to prevent harmful blood clots and inflammation. But if the endothelium is damaged, these processes may not work effectively, which is known as ‘endothelial dysfunction’.
Endothelial dysfunction is a key factor in the development of heart and circulatory conditions. For example, it is linked to the formation of fatty plaques in our arteries, which can rupture, leading to heart attacks and strokes. There is evidence that endothelial dysfunction is linked to more severe forms of Covid-19.While it’s now thought that newer and now much more common variants of the virus (such as Omicron) may not impact the endothelium as much as previous variants, endothelial dysfunction likely also plays a role in the symptoms of long Covid.