New research has shed light on how “good cholesterol” can help SARS-CoV-2, the virus that causes Covid-19, sneak into cells and infect the body.

When SARS-CoV-2 invades the body, the spike protein on the virus binds to a receptor on the host cell known as ACE2. A bit like a lock and key, this opens up the cell and allows the virus to enter. However, the new research highlights the role of another receptor, called SR-B1, that usually binds high-density lipoprotein (HDL), better known as “good cholesterol”.

In the study, published in the journal Nature Metabolism, scientists from the Academy of Military Medical Sciences in China showed how the spike protein of the virus latches on to HDL cholesterol and effectively hijacks the cell’s cholesterol-uptake machinery to gain access to host cells. When the scientists blocked the SR-B1 cholesterol receptor in the cells, it slowed down the uptake of the virus. This was only demonstrated in a petri dish, but the researchers argue that SR-B1 is present in the lower respiratory tract, so it likely does show a real way in which the virus can infect cells.

Cholesterol is a waxy substance that circulates in your blood and is mainly made by your liver, although some is drawn from your diet. While having high cholesterol can cause a load of health problems, it's not inherently “bad” and your body requires it to build cell membranes, certain hormones, and vitamin D. 

This new study should not necessarily cause further worry for people with existing health conditions. Some news reports have taken this study to suggest it explains why people with both Covid-19 and a metabolic disorder, such as diabetes or cardiovascular disease, are more likely to die from their infection. Indeed, people with these conditions are at a higher risk of falling fatally sick with Covid-19. However, experts argue they are most likely at a higher risk of Covid-19 due to other factors.

"We know that people with diabetes, heart disease, and those from BAME [Black, Asian, and Minority Ethnic] backgrounds who are at higher risk from Covid, often have low levels of HDL-C, so there is no obvious link,” commented Dr Riyaz Patel, a Professor of Cardiology at University College London, who was not involved in the study.

“Similarly those with high HDL-C levels need not be alarmed either, as there is nothing to suggest they are at higher risk from Covid. If anything, factors that increase HDL-C (such as regular exercise) are much more important in protecting against ill-health in general.” 

“People with diabetes or cardiovascular disease usually have lower, rather than increased, concentrations of HDL in their plasma and so this would not explain why they are at increased risk of serious complications from Covid-19. They are probably at higher risk of Covid-19 due to other factors,” added Professor David Leake, from the Institute of Cardiovascular and Metabolic Health Research at the University of Reading UK.

Nevertheless, independent experts have noted the research is “interesting and entirely novel.” One of the most promising parts of the research is that it could pave the way towards new treatments against Covid-19. In theory, a drug blocking the SR-B1 cholesterol receptor may help limit SARS-CoV-2 infection. However, given the importance of SR-B1 for other functions in the body, this may not be an easy task.