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Study suggests higher BMI is a greater risk factor for younger people with COVID-19

Rod Tucker
10 May, 2021  

Obesity is associated with worse outcomes in those with COVID-19 but a large study has indicated that this might only be relevant to younger and ethnic minority individuals.

Several analyses have suggested that obesity is a risk factor for severe outcomes in those with COVID-19. Other known factors include increasing age and the presence of various co-morbidities such as type 2 diabetes and hypertension. However, the extent to which each of these factors interact with excess weight has not be determined. Furthermore, it is possible that the significance of obesity as a risk factor may not be relevant and simply due to collider bias. For example, early reports that smoking, representing the collider variable, appeared to reduce the risk of COVID-19 infection, may have arisen simply because the cohort contained fewer smokers. Similarly, as studies have examined the outcomes of those admitted to hospital and who progressed to intensive care and/or death, it is unclear whether obesity or the severity of infection were the main factors driving admission and that ultimately, the link between obesity and disease severity might be spurious. This led a team from the University of Oxford, UK, to explore the effect of body mass index (BMI) and severe outcomes in COVID-19 and to examine the interaction with other demographic factors. The researchers used data from over 1500 English general practices that included demographic, diagnostic and laboratory data and which was linked to the Public Health England COVID-19 database of positive tests and these values were adjusted for in multivariate models. Data were collected between January and the end of April 2020.

Findings
Among 6,910695 eligible individuals with a mean BMI of 26.8 kg per meter squared, 0.2% (13,503) were admitted to hospital, 0.02% (1601) to an intensive care unit (ICU) and 0.08% (5479) died. In the fully adjusted models, there was a non-linear association between BMI and hospital admission and death due to COVID-19 such that each unit increase in BMI above 23 was associated with an increased risk of hospitalisation (hazard ratio, HR = 1.04, 95% CI 1.04 – 1.05), ICU admission (HR = 1.09) and death (HR = 1.04). Interestingly, there was a significant interaction between BMI and self-reported ethnicity, with Black people having a higher slightly risk than White people of hospital admission (HR = 1.07) and COVID-related death (HR = 1.08). It was also found that among younger (20 – 39) versus older (80 – 100 years) individuals with a BMI greater than 23, the risk of hospital admission was increased (HR = 1.09).

Commenting on their findings, the authors described how the data indicated a “J-shaped” relationship between increasing BMI and hospital admission. Thus, the risk was higher for those with a BMI less than 20 and started to rise again in an approximately linear manner, for those with a BMI greater than 23. In contrast, the risk of death only increased in people with a BMI greater than 28 and this rise was largely independent of other co-morbidities. They concluded on how the findings emphasised the importance of excess weight as a factor in severe COVID-19 outcomes and that efforts should be directed towards achieving a healthy weight in the wider population.

Citation
Goa M et al. Associations between body-mass index and COVID-19 severity in 6·9 million people in England: a prospective, community-based, cohort study. Lancet Diabetes Endocrinol 2021