Why are overweight people more likely to be severely ill with COVID?

By Dr. Eddie Chaloner - Consultant Vascular Surgeon




It’s a well-known fact that being substantially overweight is a major risk factor for many illnesses. We have known for many years that diabetes, arthritis, vascular disease and some cancers are all more common in overweight people.


The COVID pandemic has highlighted this vulnerability. The two major risk factors for being seriously ill or dying from COVID are advanced age and being overweight. About 30% of the UK population are classified as overweight on the basis of Body Mass Index – a calculation based on measurement of height and weight. This is by no means a perfect metric, but easy to calculate. Around half of the severely ill patients admitted to Intensive care during the pandemic had a BMI over 30 and being severely overweight (BMI over 40) was particularly dangerous. Why is this?

When I was a medical student in the 1980’s we thought of body fat as being a store of calories and not much else.


Being overweight was only thought damaging to one’s joints due to carrying an excess load and probably to the circulatory system by raising the resistance the heart needed to pump against. We now know that large amounts of fat are far more damaging to health because overburdened fat cells are highly metabolically active – in layman’s terms, excessive fat tissue pushes out chemicals that create a low level of generalised inflammation in the body. Furthermore, particular types of processed food commonly consumed by the overweight are thought to cause ‘leaky gut syndrome’, whereby fragments of intestinal bacteria escape into the bloodstream and generate inflammatory responses.


Inflammation is the process by which the body responds to injury – whether that is an infection or physical injury. It is a very necessary process which functions via a number of chemical pathways, all of which have regulatory systems within the body. However, as with many biochemical mechanisms, if the inflammatory process gets out of control, a lot of damage can ensue, and this is how obesity causes many of its harmful effects.


The COVID virus also causes severe illness by creating out of control inflammation, principally in the tiny blood vessels of the lungs, kidneys and brain. The inflamed blood vessels frequently clot, causing all sorts of problems such as kidney failure, reduced oxygen transfer in the lungs and strokes in the brain. We know from several recent studies that obese people mount an excessively exuberant inflammatory response to COVID infection, which exacerbates the effect of the virus. Some people with normal body weights also suffer severe inflammation from COVID for reasons we do not yet understand, although studies have suggested there may be an underlying genetic predisposition in those cases.


Obesity in the UK population is a relatively recent phenomenon – we know from historical data that it has only really become a public health problem in the last 3 decades. Our recent understanding of the cause of obesity has also changed. The mathematical assumption that being overweight was a consequence of eating more calories than one burned through physical activity, has given way to a more nuanced model relating to the types of food consumed. We now understand there are subtle but measurable interactions between the sort of food one eats and the bacteria in our intestines, which have significant effects on fat storage and the metabolic influence of fat tissue.


Over the last 20 years more and more evidence has accumulated supporting the health benefits of a Mediterranean style diet, heavy on fresh fruit, vegetables, olive oil, fish and best of all, red wine. Simply put, if you stick to fresh food, avoid processed products, eat a bit less meat and do a modest amount of physical exercise, you won’t go far wrong or get significantly overweight. You will probably live longer, feel better and are unlikely to become seriously ill with COVID.


Published by By Dr. Eddie Chaloner, Consultant Vascular SurgeonMA(Oxon) BM BCh FRCS(Edin) FRCS (Gen) About Dr Loxley @drloxleycare www.drloxley.com Dr Loxley is a healthcare navigation service, connecting patients to the best doctors and treatment options, supporting efficient, timely personal health decisions. We combine person clinical overview with the Loxley HealthBot, powered by patient records gathered by the team, to make every health decision more accurate and cost effective. A global network of the very best doctors and the leading digital health tools our aim to get patients in front of the right doctor, first time.