People whose diets were based on healthy plant-based foods such as fruits and vegetables had lower risks of getting Covid-19 and of having severe disease after infection, finds a study.

Although metabolic conditions such as obesity and Type 2 diabetes have been linked to an increased risk of Covid-19, as well as an increased risk of experiencing serious symptoms once infected, the impact of diet on these risks is unknown.

The study led by researchers at Massachusetts General Hospital (MGH) and published in the journal Gut, suggests that public health strategies that improve access to healthy foods and address social determinants of health may help to reduce the burden of the Covid-19 pandemic.

The beneficial effects of diet on Covid-19 risk seemed especially relevant in individuals living in areas of high socioeconomic deprivation.

For the study, the team examined data on 5,92,571 participants living in the US and the UK from March 24, 2020 and followed them until December 2, 2020.

During follow-up, 31,831 participants developed Covid-19. Compared with individuals in the lowest quartile of the diet score, those in the highest quartile had a 9 per cent lower risk of developing Covid-19 and a 41 per cent lower risk of developing severe Covid-19.

"These findings were consistent across a range of sensitivity analysis accounting for other healthy behaviors, social determinants of health and community virus transmission rates," said lead author Jordi Merino, a research associate at the Diabetes Unit and Center for Genomic Medicine at MGH.

"Although we cannot emphasise enough the importance of getting vaccinated and wearing a mask in crowded indoor settings, our study suggests that individuals can also potentially reduce their risk of getting Covid-19 or having poor outcomes by paying attention to their diet," added Andrew Chan, a gastroenterologist and chief of the Clinical and Translational Epidemiology Unit at MGH.

The researchers also found a synergistic relationship between poor diet and increased socioeconomic deprivation with Covid-19 risk that was higher than the sum of the risk associated with each factor alone.

"Our models estimate that nearly a third of Covid-19 cases would have been prevented if one of two exposures -- diet or deprivation -- were not present," says Merino.