Table 1.

A summary of the range of evidence linking obesity to adverse COVID-19 outcomes following SARS-CoV2 infection

	Current evidence	Future research ideas
Epidemiological	Multiple studies—of varying veracity—show higher BMI broadly linearly linked to worse COVID-19 outcomes, including at least a dozen meta-analyses. Where examined, links between BMI and mortality are stronger than links between BMI and non-COVID-related mortality, as well as far stronger than prior links between BMI and influenza or adult respiratory distress syndrome (ARDS).	More evidence of links of differing adiposity measures to COVID-19 would be useful.
Genetic	A recent Mendelian randomisation study in those of European Ancestry found obesity to be a likely causal risk factor with a 14% (95% CI 7 to 21%) higher risk for hospitalisation due to COVID-19 per every 1kg/m2 higher BMI. No other causal risk factors were identified though more power needed in future studies.	Validation of these genetics’ findings will come soon and should expand to other measures of adiposity and in differing ethnic groups.
Interventions	There are no trials as such, but a retrospective bariatric surgery analysis suggests people who lose (around 12 BMI units) weight through bariatric surgery are at 69% lower risk of hospitalisation and lower risk for ICU admission than pre-surgery BMI-comparable people who had not undergone surgery.	It remains unclear whether formal trials of weight loss can be large enough to prove intentional weight loss protects against adverse COVID-19 outcomes. However, it may be possible that randomised trials of weight loss-promoting drugs, if enough people in trials did develop COVID-19 and robust outcome data were recorded, could prove the weight loss theory.
Biological plausibility	Obesity contributes to metabolic derangements, worse lung and kidney function, poorer vascular health, and is associated with a low-grade inflammation and a greater thrombogenic potential. In this way, obesity lessens an individual’s capacity to cope with the systemic effects of the hyperimmune response.	Understanding how excess fat stores or adipose tissue impairs the immune response, in general and in COVID-19, requires dedicated research