The theme of food-related inflammation has been dominant over the past decade. As a result, new tools have emerged to measure this state as well as to strengthen its association with adverse health outcomes. A new report looks at dietary inflammation and its effect on rates of coronavirus disease 2019 (COVID-19), severity, and death.

Study: Diet-Related Inflammation Is Associated with Worse COVID-19 Outcomes in the UK Biobank Cohort. Image Credit: RomarioIen / Shutterstock

Introduction

Much research already exists to show that obesity is a state of low-level inflammation and a risk factor for severe and critical COVID-19 and higher mortality rates among COVID-19 patients. Even earlier investigations demonstrated the crucial role of diet in an effective and regulated inflammatory and immune response to infectious pathogens. However, little is known about how nutrition impacts COVID-19.

Nutrients do not come as separate packages. Therefore, many scientists have suggested that the best way to establish an appropriate nutritional protocol for managing and preventing severe COVID-19 would be to evaluate dietary profiles. For instance, plant-based diets like the Alternative Mediterranean Diet (AMED) or Alternative Healthy Eating Index (AHEI)-2010 seem to be linked to lower rates of COVID-19.

The current study, published in the journal Nutrients, explores the role of dietary patterns in COVID-19 infection rates and survival. It uses the Dietary Inflammatory Index (DII®) in association with measures of COVID-19 infection, severity and death.

The DII was meant to assess the effects of diet on inflammation in quantitative terms, measuring gut symptoms linked to infection. A higher DII score indicates a pro-inflammatory diet, and the researchers explored the risk of COVID-19, disease severity, and mortality with higher DII scores.

The underlying biological hypothesis is that dietary factors can be converted into cytokines that affect inflammatory and immune responses. In addition, dietary bioactives may themselves hijack other nutrients into distinctive metabolic pathways that affect inflammation.

The omega-3 fatty acids are anti-inflammatory in their effect, for instance, because they encourage the anti-inflammatory lipo-oxygenase rather than the cyclo-oxygenase pathway, which is pro-inflammatory. These fatty acids also give rise to an array of other molecules that regulate acute inflammation and immune responses, which are essential to combat the infection and trigger the adaptive immune response. Importantly, this also prevents chronic inflammation, which would cause a state of immunocompromise and ineffective inflammation.

Metabolic syndromes such as obesity and type 2 diabetes conform to this chronic inflammatory state, making the patient less able to respond to infectious pathogens like the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes COVID-19.

The study was based on a large population-based cohort, the UK Biobank, with over 500,000 participants between the ages of 37 and 73. Of these, almost 200,000 had the data from which the DII or the modified E-DII (energy-DII) scores could be calculated.

What did the study show?

There were 1270 COVID-19 cases with severe disease in this group of ~200,000, with 315 deaths. The DII scores fell between -4.3 and 3.4, vs. E-DII between -4.9 and 3.3. The medians were -0.4 and -0.5, respectively.

The highest DII scores were in younger, heavier participants, with higher scores on the Townsend Deprivation Index. In addition, this group had a higher smoking prevalence, lower physical activity and a higher prevalence of cancer.

Both DII and E-DII were linked to COVID-19, with the risk being 10% and 17% higher, respectively, in the highest quintiles of each score, vs. the lowest quintile. The risk was higher among never-smokers. The increase began to appear from the third quintile and steadily rose thereafter.

Both were linked to a risk increase for severe COVID-19 by ~40% in the top quintile vs. the lowest. Neither was significantly linked to COVID-19-related deaths, however, most probably because of the low numbers in this scenario. Other factors, such as racial, ethnic, sleep history, and a history of heart disease, did not affect these associations with COVID-19 incidence or severity.

About a fifth to a quarter of the risk association was mediated by an increased body mass index (BMI), used here as a proxy for fat deposition.

What are the implications?

The risk of COVID-19 and severe disease was consistently associated with higher DII and E-DII scores, partly because of obesity. However, future studies with more significant numbers would be required to establish the association, or lack thereof, with COVID-19 mortality, given the <3% confirmed infection rate in this cohort, with <0.2% reported to have died of COVID-19-related causes.

Other studies have shown that diets with lower inflammatory scores reduce the risk of COVID-19 by 10% to 20%, with the Mediterranean diet profile consistently showing an inverse association with this outcome.

“Results from this study are consistent both with the protective effects of an anti-inflammatory diet (which allows for a competent acute pro-inflammatory response) and the chronic pro-inflammatory effect of high levels of adiposity.”

This finding, coming from a large, prospective, fully-adjusted study that uses standardized, generalizable, and validated indices for dietary quality, is a strong indicator of the importance of diet quality in determining health outcomes.

“Improvement in dietary patterns may be beneficial in reducing the risk of COVID-19 and similar infections.”

Journal reference:

• Zhao, L. et al. (2023). Diet-related inflammation is associated with worse COVID-19 outcomes in the UK Biobank cohort. Nutrients. doi: https://doi.org/10.3390/nu15040884,  https://www.mdpi.com/2072-6643/15/4/884