Body mass index and the risk of COVID‐19 across ethnic groups: Analysis of UK Biobank

To the Editor:

Coronavirus disease‐2019 (COVID‐19), an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2 virus), has devastated global economies and put unprecedented strain on clinical services. Emerging evidence has suggested that black and minority ethnic (BME) groups, particularly South Asian (SA) and black African or Caribbean (BAC) populations, are at an increased risk of COVID‐19 and resulting complications. ¹ Obesity is also associated with a higher risk of testing positive for, and dying from, COVID‐19. ¹ , ² However, the interaction between ethnicity and obesity on the risk of COVID‐19 has not been tested. As ethnicity is known to modify the association between body mass index (BMI) and cardiometabolic health, ³ , ⁴ we hypothesise that BMI also acts to modify the relative risk of COVID‐19 across ethnic groups.

We used UK Biobank, a large prospective cohort of 502 543 individuals with baseline assessments conducted from March 2006 to July 2010. ⁵ UK Biobank data were linked to national COVID‐19 laboratory test data through Public Health England. ⁶ Data were available for the period from 16 March to 14 June 2020.

We undertook an adjusted logistic regression to (a) quantify the association of BMI with the risk of a positive test for COVID‐19, stratified by ethnic group, and (b) investigate whether the odds of COVID‐19 in BME (SA and BAC) individuals relative to white Europeans (WEs) varied by BMI level. Non‐linear interactions were investigated using restricted cubic splines with knots placed at the 33th and 66th centile of BMI distribution. Models were adjusted for potential confounders (Figure 1) and the interaction was formally assessed using the likelihood ratio test.

FIGURE 1.

Association of body mass index (BMI) with confirmed COVID‐19 in white European (WE) and black and minority ethnic (BME) individuals. Odds ratio (OR) for COVID‐19 with BMI stratified by BME and WE groups (left) and in BME relative to WE (right). Reference (OR 1) were placed at BMI of 25 kg/m². OR (lines) and confidence intervals (CI; areas) are plotted across continuous BMI values (x axes) between the 2.5th (20 kg/m²) and 97.5th (39 kg/m²) centile of the distribution. Shaded area as 95% CI. Analysis adjusted for: age at test, sex, social deprivation (Townsend score), smoking status, cancer illnesses (number) and non‐cancer illnesses (number), systolic blood pressure, HDL‐cholesterol, total cholesterol and HbA1c

There were 5623 unique test results available (WE: 5352; BME: 271), of which 1087 (19.3%) were positive (WE: 1000 [18.7%]; BME: 87 [32.1%]). WE individuals with test data had a median (IQR) age of 71.3 (62.3, 76.1) years, a BMI of 27.6 (24.8, 30.9) kg/m² and 2650 (49.5%) were women. Comparatively, BME individuals were 64.8 (57.9, 73.2) years old, had a BMI of 28.2 (25.2, 33.1) kg/m² and 136 (50.2%) were women. The majority of the BME population (83%) were first‐generation migrants to the UK.

BMI was associated with the risk of a positive test for COVID‐19 in both BME and WE individuals. However, the dose response association differed by ethnic group (P for interaction = .05) (Figure 1): in WE individuals, there was no additional higher risk of COVID‐19 beyond a BMI of 25 kg/m², whereas in BME individuals the risk was greater for higher BMI values. Greater risk of COVID‐19 in BME individuals relative to WEs was only apparent at higher BMI values (Figure 1). For example, at a BMI value of 25 kg/m², there was no difference in risk (OR = 0.96; 95% CI: 0.61, 1.52), whereas at a BMI of 30 or 35 kg/m², the odds of COVID‐19 were 1.75 (1.24, 2.48) and 2.56 (1.63, 4.03) higher in BME individuals relative to WEs, respectively.

Although limited by non‐random testing for COVID‐19 within the UK, these data suggest that the association between BMI and the risk of COVID‐19 may vary by ethnicity and act as an important effect modifier for the increased risk of COVID‐19 in BME populations. These results suggest that the combination of obesity and BME status may place individuals at a particularly high risk of contracting COVID‐19, consistent with findings for associations of BMI and ethnicity with cardiometabolic dysfunction. ³ , ⁴

CONFLICT OF INTEREST

None declared.

FUNDING INFORMATION

This work was supported by the NIHR Leicester Biomedical Research Centre.

AUTHOR CONTRIBUTIONS

Concept and design: C.R., T.Y. and K.K. Acquisition, analysis or interpretation of data: all authors. Drafting of the manuscript: C.R. and T.Y. Critical revision of the manuscript for important intellectual content: all authors. Statistical analysis: C.R. and T.Y. Statistical oversight: F.Z. Note that K.K. and T.Y. are joint senior authors.