Update on nutrition and lifestyle factors and COVID-19, 11th September 2022

It has been a few months since I wrote on this topic. During this time, we have created two new COVID-19 factsheets. It seems timely to provide an update.

I have been following with great interest the studies on diet, nutrition and COVID-19 outcomes. My previous summary articles can be found here (make sure you scroll down for recent updates). To date, we have learnt that a healthy diet is key to maintaining physical and mental well-being. Diet and lifestyle-related chronic conditions worsen outcomes and increase the risk of death with COVID-19. High cholesterol, high blood glucose along with poor vascular health enhances the viruses’ ability to cause damage to cells, blood vessels and organ function. The health of the gut microbiome is associated with severity of infection and a healthy plant-based diet may be a useful tool for reducing the impact of the pandemic virus.

We now have information on the impact of other healthy lifestyle habits and also more robust studies to inform our practice. Given that COVID-19 is going be with us for the foreseeable future, we need to shift focus to optimising health and wellbeing. In addition, the broader implications need to be addressed, including the prevention of future pandemics by addressing the climate crisis and abolishing factory farming.

PHYSICAL ACTIVITY AND COVID-19: To date I have concentrated on the impact of diet on COVID-19 outcomes. However, there are data now to support other healthy lifestyle habits.

The large study highlighted brings together data from 16 studies including 1, 853 610 adult participants with an average age of 53 years. The study specifically examines the association between physical activity and risk of COVID-19 infection, hospitalisation, disease severity and death. Most of the studies were observational and were carried out in South Korea, England, Iran, Canada, the UK, Spain, Brazil, Palestine, South Africa and Sweden.

The results showed that regular physical activity lowered the risk of COVID-19 infection by 11%, risk of hospitalisation by 36%, severe illness by 34% and the risk of dying by 43%. The greatest benefit was seen in participants achieving 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity physical activity per week, which is in line with current guidelines.

We known that regular physical activity improves immune function, promotes insulin sensitivity, reduces inflammation and oxidative stress and favourable impacts the health of the gut microbiome. In addition, physical activity helps to maintain optimal cardiometabolic health. All of these factors are likely to have played a role in the results demonstrated.

This should really come as no surprise given that previous data has also demonstrated the ability of physical activity to reduce the risk and severity of infections in the community. Although we can not prove cause and effect from the available data, there is no downside to regular physical activity with benefits for both physical and mental wellbeing. I fully acknowledge that safe and accessible spaces for physical activity are not available to all in society and thus Governments and policy makers need to address this inequity of access.

HIGH-DOSE VITAMIN C SUPPLEMENTATION: I was surprised to see the positive results in favour of vitamin C supplementation in this study. The paper includes an analysis of 15 studies involving 2125 participants with COVID-19. Six studies were randomised controlled studies and the remainder retrospective in design. Most studies used intravenous vitamin C where as two used oral supplementation. Doses ranged from 1–12 grams per day.

The results show a significant reduction in severity and risk of death from COVID-19. However, there are some caveats to these data. Overall, the total number of participants is relatively small, the dose and administration of vitamin C variable, and a prior meta-analysis failed to show a benefit.

For me the main question is how these results relate to the impact of a healthy diet and lifestyle habits and the presence of other cardiometabolic diseases. We don’t have data on diet quality in these participants. Nonetheless, it is important to note the beneficial impact of vitamin and minerals found in whole plant foods on immune health. These phytonutrients reduce inflammation and oxidative stress whilst promoting better cardiometabolic health.

VITAMIN D SUPPLEMENTATION AND COVID-19: Adequate vitamin D is essential for immune health. Prior data have shown that vitamin D levels are associated with the risk and severity of COVID-19. So the obvious question is whether supplementation with vitamin D is beneficial. Two studies published in the BMJ call into question the value of vitamin D supplementation, although there are several caveats to the data and as the accompanying editorial suggests, ‘this won’t be the final word’.

The first study was conducted in the United Kingdom. 3100 participants were randomised to a vitamin D test and either 3200 IU/day or 800 IU/day of vitamin D3 for six months if their blood vitamin D levels were <75 nmol/L. A control group of 3100 people were not tested and did not receive supplementation. The results did not find a benefit for COVID-19 outcomes for the supplementation group. The study results are slightly muddied by the vaccination programmes taking place at the same time, but results did show a benefit of supplementation for unvaccinated participants. In addition, 50% of the control group were also taking vitamin D supplements, which may have masked any potential benefits in the intervention arms.

The second study was conducted in Norway and randomised 34,741 participants to either 5ml cod liver oil or 5ml placebo oil daily for six months. Again, there was no benefit of supplementation seen for COVID-19 outcomes. However, most people in this study had normal vitamin D levels at baseline.

Like with most supplementation studies, more may not be better. However, this does not take away from the fact that adequate vitamin D status is important for overall health, including immune health. The pragmatic advice remains that if you are not able to get sufficient exposure to sunlight then vitamin D supplementation is advised regardless of diet pattern. In addition, if you know you have low vitamin D levels, then supplementation should be used to bring levels back into the therapeutic range.

GUT HEALTH, LIPID LEVELS AND COVID-19: This study is only in pre-print version so far (not peer reviewed or published in a medical journal). The researchers explored the health of the gut microbiome and metabolic blood markers, including cholesterol, in people who had already experienced COVID-19 infection in the community and compared the results to individuals with non-COVID-19 illnesses of prolonged duration. The aim was to identify risk factors associated with long symptom duration.

Study participants were volunteers from the COVID Symptom Study Biobank (CSSB). Participants were categorised in to four groups (i) asymptomatic COVID-19 group; (ii) short COVID-19 duration (≤2 weeks); (iii) long COVID-19 duration (≥28 days); and (iv) long symptom duration (≥28 days) of non-COVID-19 illnesses.

The results showed higher blood levels of LDL-cholesterol and triglycerides were associated with a longer duration of COVID-19 symptoms, whereas higher blood levels of polyunsaturated fatty acids were associated with reduced duration. These results were similar in participants with COVID-19 and non-COVID-19 infections.

Surprisingly, no significant associations were found between the duration of illness and the health of the gut microbiome. This may be due to the cross-sectional nature of the study and prospective studies may demonstrate different results. One previous study has demonstrated altered gut microbiome composition in individuals with persistent symptoms after COVID-19 infection compared to healthy historical pre-pandemic controls. However, this study was in hospitalised patient who had already received antibiotics.

METABOLIC MAYHEM AND COVID-19: It has been clear from the start of the pandemic that individuals with cardiometabolic conditions, including heart disease, high blood pressure and cholesterol and type 2 diabetes, have a significantly increased risk of a poor outcomes from COVID-19 infection. Non-alcoholic fatty liver disease (NAFLD) is no exception and is often found in conjunction with other cardiometabolic conditions, when it is referred to as MAFLD — metabolic dysfunction-associated with fatty liver disease. Prior data from the UK biobank study suggested that the increased risk from COVID-19 in people with obesity may in fact be due to the presence of fatty liver disease.

The study highlighted examines the impact of both NAFLD and MAFLD on COVID-19 outcomes. The retrospective study included 359 hospitalised patients with confirmed COVID-19 infection in a tertiary referral hospital. The results showed that a diagnosis of MAFLD significantly increased the risk of dying from COVID-19, but NAFLD did not. However, both NAFLD and MAFLD increased the risk of requiring intubation (being on a ventilator).

This brings us back to the importance of cardiometabolic health. All chronic health conditions are related to a small number of risk factors. That is, unhealthy diet, lack of physical activity, tobacco smoking and alcohol consumption. NAFLD is a condition associated with excess calorie consumption and particularly associated with a diet that is high in meat and ultra-processed foods whilst being insufficient in healthy plant foods and fibre. NAFLD is associated with overweight and obesity but can occur in people of seemingly normal body weight. This is because we all have different ‘fat threshold’s or tolerance’, the point at which we start laying down visceral fat (the dangerous type that is present in our body organs, rather than the less dangerous type under the skin). Visceral fat leads to inflammation, insulin resistance and type 2 diabetes.

The good news is that fatty liver disease and other metabolic conditions associated with excess visceral fat can be reversed adopting a healthy diet and lifestyle. Any diet that can result in a calorie deficit will ultimately lead to a reduction of visceral fat. A healthy and sustainable way to do this is by adopting a whole food plant-based diet which is naturally lower in calories whilst being nutrient and fibre-rich, thus supporting longer-term health.

ETHNIC DIFFERENCES IN OBESITY AND COVID-19 OUTCOMES: Early on in the pandemic it became clear that people on non-White ethnicities had a higher risk of death from COVID-19. Subsequent research has shown that there are a number of factors contributing to this finding, including socioeconomic determinants, systemic racism and also the prevalence of underlying health conditions, including obesity. Obesity, defined as a BMI >30kg/m2 is associated with an increased risk of severe COVID-19 and death. The paper highlighted examines the combined impact of obesity and ethnicity on COVID-19 outcomes.

The study linked national Census, electronic health records and mortality data for adults in England from January 2020 to December 2020. The analysis included 11,074,708 white, 416,542 Black, 621,691 South Asian and 478,196 people from other ethnic minority groups with linked BMI data from family practices in England. During this time period there were 30,067 (0.27%), 1,208 (0.29%), 1,831 (0.29%), 845 (0.18%) COVID-19 deaths in White, Black, South Asian and other ethnic minority groups, respectively.

BMI was associated with COVID-19 mortality in all ethnic groups. A BMI of 40 kg/m2 was associated with a 73%, 300%, 525% and 389% increased risk of death in White, Black, South Asian and other ethnic minority groups respectively, compared to the reference of a BMI of 22.5 kg/m2 in White ethnicities. At a low BMI of 20 kg/m2, there was no difference in the risk of COVID-19 mortality in Black or other minority ethnicities relative to white ethnicities and only a marginally elevated risk in South Asian ethnicities. However, the estimated risk of COVID-19 mortality at a BMI of 40 kg/m2 in white ethnicities was equivalent to the risk observed at a BMI of 30.1 kg/m2, 27.0 kg/m2, and 32.2 kg/m2 in Black, South Asian and other ethnic minority groups, respectively.

In simple terms, the impact of obesity is much greater in people of non-White ethnicities and the higher risk of death is observed at a lower BMI compared with people of white ethnicities. The reasons for this are not clear, although hypotheses include the fact that non-White ethnicities have a higher propensity to laying down visceral fat and may have a higher inflammatory response to carry too much weight.

The reasons matter less than the potential solutions. Diet and lifestyle habits are fundamental for maintaining a healthy weight. I also acknowledge that systemic chances need to occur to ensure everyone has access to a healthy diet and to make better lifestyle choices.

Some recent papers add to the already abundant data supporting the role of healthy plant-based diets for improving health. A systematic review of nine prospective cohort studies finds that a healthy plant-based diet protects against weight gain and adiposity. Vegetarian and vegan diets protect against heart disease. A particularly relevant paper reports results from the MASALA (Mediators of Atherosclerosis in South Asians Living in America) study, a prospective cohort of South Asians in the US. The results show that a healthy plant–based diet was associated with better glucose control, lower insulin resistance, a lower body weight, a lower BMI and a lower incidence of type 2 diabetes. Each 5-unit higher adherence to a healthy plant-based diet (scoring between 20–100 points) was associated with an 18% reduction in the risk of type 2 diabetes. The study emphasises the importance of diet quality given that most study participants are vegetarian. The authors also highlight the co-benefits for planetary health ‘In addition to its health benefits, a healthy plant–based diet is also environmentally sustainable, as it is in line with the universal healthy reference diet recommended by the EAT-Lancet commission on healthy diets from sustainable food systems’.

PREVENTING THE NEXT PANDEMIC: We understand clearly that the best way to prevent future pandemics is to change the way we use animals and their habitats. Infectious pandemic risk originates predominantly from spillover of viruses from wild and farmed animals to humans. The main drivers of these spillover events are land use change, including deforestation, expansion of agricultural land, intensive farming, animal hunting and the wildlife trade and of course climate change itself. A key element of preventing future pandemics is to shift to a plant-based food system, reducing and ultimately eliminating the use of animals for food. This is also essential to meet our climate and nature commitments and would allow us to release 75% of farm land back to nature. Even if we eliminated fossil fuel emissions today, we would still not be able to prevent global warming above 2°C without address the food system, yet eliminating animal agriculture would allow us to remove 16 years of fossil fuel-based carbon emissions from the atmosphere by the year 2050.

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