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Low BMI a risk factor for death in COVID-19

Obesity is associated with a worse prognosis among individuals with COVID-19 but less attention has been paid to those who are underweight.

During the COVID-19 pandemic, data emerged suggesting that being overweight leads to poorer health outcomes for those with COVID-19 and that such patients are more likely to require mechanical ventilation. In contrast, less is known about the possible risks associated with a lower body mass index (BMI).

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 clinical outcomes for patients with COVID-19. The team included 10,861 patients hospitalised with COVID-19 during March to the end of April 2020. The BMI was documented on admission and either self-reported or obtained from nursing staff. It was classified as follows (BMI ranges 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 outcomes were the need for mechanical ventilation and death. All patients were followed until discharge, death or until early May 2020.

The 10,861 patients had a median age of 65 years (59.6% male) with 2.2% classed as underweight, 23.1% normal, 37% overweight and 37.7% obese (classes I – III). 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 underweight patients and 73.8% of those classed as obese (all classes) required mechanical ventilation. Furthermore, 39.2% of underweight patients died as did 62.9% 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 worse outcomes after COVID-19 are not restricted to obese patients and those who are underweight also appear to be 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

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