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Low BMI increases risk of death with COVID-19

2nd December 2020

Obesity is associated with a worse prognosis among individuals with COVID-19. However, until now, no studies have examined the relationship between different body mass indices and clinical outcomes.

Preliminary data has suggested that being overweight can contribute towards poorer health outcomes for those with COVID-19 and such patients are more likely to require mechanical ventilation. In contrast, far less attention has been paid to the possible relationship between low body mass index (BMI) and clinical outcomes. As a result, a team from the Department of Medicine, Donald and Barbara Zucker School of Medicine, New York, USA, set out to retrospectively analyse the overall association between different levels of BMI and outcomes for patients with COVID-19. The team included 10,861 patients admitted with COVID-19 into their hospital during March to the end of April 2020. The BMI was documented on admission to hospital as either self-reported or obtained from nursing staff. It was classified as follows with the BMI range in brackets: underweight (under 18.5kg/m2), normal (18.5 to 24.9), overweight (25 to 29.9) and obese class I (30 – 34), II (35 – 39) and III (40 or more). Data on patient outcomes were collected from electronic health records and the primary outcome used was the need for mechanical ventilation and death. All patients were followed until discharge, death or until early May 2020.

For the 10,861 patients with a median age of 65 years (59.6% male), 2.2% were classed as underweight, 23.1% normal, 37% overweight and 37.7% obese. In total, 2,220 (20.4%) patients required mechanical ventilation and 2,596 (23.9%) died. There were significant differences in both the need for mechanical ventilation and death among the different BMI categories. For instance, 12.4% of those classed as underweight and 73.8% of those classed as obese (all classes) required mechanical ventilation. In addition, 39.2% of those who were underweight died as did 62.9% of those in the obese category. Regression analysis revealed that patients who were underweight an increased risk of death (hazard ratio, HR = 1.46, 95% CI 1.17 – 1.81) which was actually higher than the risk for those with class III obesity (HR – 1.23, 95% CI 1.03 – 1.48). The reason for the increased risk of death among underweight patients was unclear but the authors speculated that this may have been related to increased frailty.

They concluded that the findings suggest that worse outcomes after COVID-19 are not restricted to obese patients and those who are underweight are also at a higher risk.

Kim T et al. Body Mass Index as a Risk Factor for Clinical Outcomes in Patients Hospitalised with COVID- 19 in New York. Obesity 2020