Risk of COVID‐19 for patients with obesity
Even though there are very few available data on BMI (body mass index) for patients with COVID‐19 infections, the role of obesity in the COVID‐19 epidemic must not be ignored. Obesity plays an important role in the pathogenesis of COVID‐19 infection. In fact, the immune system, which is a key player in the pathogenesis of COVID‐19, also plays an important role in obesity‐induced adipose tissue inflammation. This inflammation of adipose tissue results in metabolic dysfunction potentially leading to dyslipidaemia, insulin resistance, type 2 diabetes mellitus, hypertension, and cardiovascular disease.
By analogy to other respiratory infections, obesity may play an important role in COVID‐19 transmission. For example, in the case of influenza A, obesity increases the duration of virus shedding; symptomatic patients with obesity shed virus 42% longer than adults who do not have obesity.1 In H1N1 influenza, obesity is an independent risk factor for hospitalization and death.2
Since obesity has been shown to increase vulnerability to infections, it may be a risk factor for COVID‐19‐related mortality.3 This is all the more so since there are no specific clinical signs that foreshadow the progression from a mild COVID‐19 infection to a severe form. Compared with normal patients, BMI was significantly higher in patients with a severe form of COVID‐19 infection (27.0 ± 2.5 [critical group] versus 22.0 ± 1.3 [general group]; P < 0.001).4 Peng et al. published a retrospective analysis on 112 patients with COVID‐19 infection admitted to the western district of Union Hospital in Wuhan, from 20 January 2020 to 15 February 2020. In this study, the BMI of the critical group (25.5 [23.0, 27.5] kg/m2) was significantly higher (P = 0.003) than that of the general group (22.0 [20.0, 24.0] kg/m2). Patients were further divided into two groups, survivors (84.8%) and non‐survivors (15.18%). Among the non‐survivors, 88.2% of patients had a BMI > 25 kg/m2, which is a significantly higher proportion (P < 0.001) than in survivors (18.9%).5 The authors concluded that the highest BMI was more often seen in critical cases and non‐survivors. Thrombotic events were an aggravating cause of death.5 Thromboembolic risk is known to be higher in patients with obesity than in the general population.6 It logically follows that obesity can be an aggravating risk factor for death from COVID‐19 infection.
One explanation of the above findings is that COVID‐19 has high affinity for human angiotensin converting enzyme 2 (ACE2). ACE2 has been shown to be the putative receptor for the entry of COVID‐19 into host cells.7 Tissue expression of ACE2 differs in kidneys, heart, and lungs of healthy patients and coronavirus‐infected patients.8 The level of ACE2 expression in adipose tissue is higher than that in lung tissue, a major target tissue affected by COVID‐19.9 This is an important finding because adipose tissue might also be vulnerable to COVID‐19. It should be noted, however, that there was no difference in the expression of ACE2 protein by adipocytes and adipose progenitor cells between individuals with obesity and those without.10 However, individuals with obesity have more adipose tissue and therefore an increased number of ACE2‐expressing cells and consequently a larger amount of ACE2.9 In addition, treatments with specific anti‐hypertensive medications (angiotensin‐converting enzyme inhibitors [ACEIs] and angiotensin receptor blockers [ARBs]) will increase expression of ACE2 and increase patient susceptibility to viral host cell entry and propagation.11
Another factor might also contribute to the increased risk from COVID‐19 for patients with obesity. Adipose tissue can serve as a reservoir for human adenovirus Ad‐36, influenza A virus, HIV, cytomegalovirus, Trypanosoma gondii, and Mycobacterium tuberculosis.12 By analogy, COVID‐19 might also infect adipose tissue and then spread to other organs.
Thus, we recommend extra attention and precautions for patients with obesity during this epidemic. Whenever COVID‐19 infection is suspected, screening must be systematic, particularly if the patient has obesity. Adipose tissue can be a research model to help understand the pathogenesis of COVID‐19 infection and develop an effective treatment.