Obesity and COVID-19: are they linked? An update of the evidence

In June this year we reviewed evidence published throughout the COVID-19 pandemic that suggested a potential link between obesity and severity of COVID-19. Since then, evidence has continued to emerge, and while some limitations remain, it has become clear: there is an association between obesity, severity and worse outcomes from COVID-19.

New evidence

At the end of July, Public Health England released a report providing evidence-based insights into the relationship between excess weight and COVID-19, garnered from new evidence. They found an increased association with testing positive for COVID-19 as BMI increases above a healthy range, with a stronger relationship observed in BAME groups than in White ethnic groups. They also found that patients with a BMI in the overweight or obesity categories are more likely to be admitted to intensive care than those with BMI in the healthy range or below. They are also more likely to require advance treatment for severe symptoms. Finally, they found a potentially higher risk of COVID-19 related death with increasing BMI, which has persisted in studies adjusted for confounding factors such as age, sex, measures of socio-economic status (SES), ethnicity and co-morbidities.

The UK Intensive Care National Audit and Research Centre (ICNARC)¹ has continued to report a relationship between critical illness from COVID-19 and obesity, with 39.3% of ICU patients with COVID-19 classed as having obesity. Researchers have also used data from the UK Biobank, a large set of data following half a million volunteers, finding that testing positive for COVID-19 is also associated with obesity².

Observations made in UK studies are consistent with international evidence; global evidence consistently highlights an association between obesity and COVID-19 hospitalisation, severity, admission to ICU, and death.

Why might people be at higher risk of complications?

Researchers have identified a number of potential mechanisms that may explain the link between obesity and COVID-19:

• Obesity causes an underlying state of inflammation in the body, which can affect its ability to fight a virus
• Obesity is a risk factor for other conditions, like type 2 diabetes. It is common for people with obesity to have several conditions at once
• Lung function, volume and capactiy is often impaired in those with obesity
• Standard treatment may be affected, for example, ‘proning’ (turning people on to their front) has become standard treatment in COVID-19 to improve oxygenation to particular areas of the lungs. In patients with obesity, this is much more difficult, and may not be possible in patients with severe obesity
• Individuals with obesity experience stigma and discrimination due to their weight. Weight stigma is associated with a reluctance to seek healthcare, can affect quality of treatment received, resulting in worse outcomes
• Satiety-regulating hormone leptin, secreted in proportion to body fat, connects metabolism to the immune response. Individuals with obesity have higher levels of circulating leptin, associated with leptin resistance. Researchers have suggested that due to its link with pulmonary immunity, leptin dysregulation may have serious consequences during COVID-19 infection

Ethnicity, area deprivation and inequalities

Since our last evidence review, more research has emerged on the link between ethnicity, area deprivation, inequalities and COVID-19. There are long-standing health inequalities in the UK that researchers believe have been exacerbated by the coronavirus pandemic, including those related to ethnicity and socio-economic deprivation.

Children living in the most deprived areas of Scotland have more than double the risk of obesity than those in the least deprived areas (13.7% vs 6.5%)³, with a similar gap seen amongst children in England⁴. This gap also exists for adults in Scotland³ and England⁴.

Evidence is emerging for an association between obesity, socioeconomic status and COVID-19, showing a social gradient with poorer outcomes for those from more socio-economically deprived areas, which is likely multifactorial:

1. Increased susceptibility due to poor pre-existing health,
2. Increased exposure due to living and working conditions (poorer housing and air quality, lower paid jobs),
3. Increased stress during lockdown due to adverse social conditions

This is backed up by recent ICNARC data, which shows that around a quarter of patients diagnosed with COVID-19 and in ICU were from the most deprived fifth of the population, compared to 14.4% from the least deprived fifth¹. This disparity is evident across all ethnic groups, however is much more pronounced in those of Non-White ethnicity compared to White individuals.

There is also a disparity in prevalence of obesity between different ethnic groups. In children in England, obesity prevalence is highest for Black children across both year groups measured (reception and year 6)⁵, while in Scotland, Black children are more likely than White children to have a high BMI⁶. Again, this is also observed in adults⁷.

Researchers have found that while the risk of testing positive for coronavirus was associated with BMI both in BAME and White ethnic groups, as BMI increased over 30 (obesity category), the likelihood of testing positive was far higher in BAME individuals than in White individuals⁸. Sattar et al recorded the same findings, and additionally found that BMI was more strongly related to COVID-19 death in Non-White individuals (predominantly South Asian and Afro-Caribbean), than White individuals⁹.

Conclusion

Obesity has well-established links with adverse health outcomes from a range of co-morbidities. Evidence emerging during the coronavirus pandemic suggests similar associations; obesity has been consistently linked to increased severity of COVID-19 and increased risk of death, with multiple potential and plausible mechanisms identified. Nevertheless, there are limitations in the evidence which should be taken into account when making recommendations¹⁰. Further research is required to explore the extent to which ethnicity and deprivation contribute to increased severity and risk of death from COVID-19.

As more data on co-morbidities and demographics of patients with confirmed COVID-19 is analysed, risk factors can be determined and groups most at risk from the virus can be identified clearly. This information can be used to tailor prevention measures toward groups who require the most protection.

Read our new briefing, Obesity and COVID-19, jointly published with the Royal College of Physicians and Surgeons of Glasgow.

References

1. Intensive care national audit & research centre. ICNARC Report on COVID-19 in Critical Care - 31st July 2020. London; 2020.
2. Yates T, Razieh C, Zaccardi F, Davies MJ, Khunti K. Obesity and risk of COVID-19: analysis of UK biobank. Prim Care Diabetes. 2020:19-20. doi:10.1016/j.pcd.2020.05.011
3. Cheong C, Dean L, Dougall I, et al. The Scottish Health Survey. 2018 Edition. Volume 1. Main Report. Edinburgh; 2019.
4. NHS Digital. Health Survey for England 2018 [NS]. London; 2019. https://digital.nhs.uk/data-and-information/publications/statistical/health-survey-for-england/2018.
5. NHS Digital. National Child Measurement Programme, England 2018/19 School Year. London; 2019. https://digital.nhs.uk/data-and-information/publications/statistical/national-child-measurement-programme/2018-19-school-year.
6. Information Services Division. Body Mass Index of Primary 1 Children in Scotland. School Year 2018/19.; 2019. https://www.isdscotland.org/Health-Topics/Child-Health/Publications/2018-12-11/2018-12-11-P1-BMI-Statistics-Publication-Report.pdf.
7. Baker BC. Obesity Statistics. 2019;(3336).
8. Razieh C, Zaccardi F, Davies MJ, Khunti K, Yates T. Body mass index and the risk of COVID-19 across ethnic groups: Analysis of UK Biobank. Diabetes, Obes Metab. 2020. doi:10.1111/dom.14125
9. Sattar N, Ho FK, Gill JM, et al. BMI and future risk for COVID-19 infection and death across sex, age and ethnicity: Preliminary findings from UK biobank. Diabetes Metab Syndr Clin Res Rev. 2020;14(5):1149-1151. doi:10.1016/j.dsx.2020.06.060
10. Blackshaw J, Feeley A, Mabbs L, Niblett P. Excess Weight and COVID-19: Insights from New Evidence. London; 2020. https://www.gov.uk/government/publications/excess-weight-and-covid-19-insights-from-new-evidence.