A study conducted by researchers from the University of North Carolina has found that having a BMI of over 30 increases the risk of dying from the disease by nearly 50 per cent.
The researchers also found that people with obesity experience physical ailments that make fighting the virus harder.
Professor Luke O'Neill, from the School of Biochemistry and Immunology at Trinity College Dublin, says the study is comprehensive.
"They looked at all these risk factors [for Covid-19] and by far and away, ageing is the biggest risk factor as we know, and obesity came up second.
"If you talk to any intensive care doctor, they will tell you that the ones who end up on ventilators or have a serious disease are inclined to have a high BMI or be obese, and this study confirms that."
This comes as the HSE CEO Paul Reid says the rise in Covid-19 hospitalisations is "concerning".
Twenty-eight people are being treated for the virus in the country's hospitals today, with four in ICUs.
