While bad cholesterol has been blamed for increasing risk of heart disease, variations in the good cholesterol levels may also lead to infectious diseases such as gastroenteritis or pneumonia, according to a study.Individuals with very low high-density lipoproteins (HDL) cholesterol had a 75 per cent higher risk of infectious disease, whereas the risk was 43 per cent higher in those with very high HDL cholesterol, the researchers said."We found that individuals with both low and high HDL cholesterol had high risk of hospitalisation with an infectious disease," said Borge Nordestgaard, Professor at the University of Copenhagen in Demark."Importantly, these groups of individuals also had high risk of dying from infectious disease," Nordestgaard added.For the findings, published in the European Heart Journal, the team examined the data from 100,000 individuals."Numerous studies in animals and cells indicate that HDL is of importance for the function of the immune system and thereby the susceptibility to infectious disease. However, this study is the first to examine if HDL is associated with the risk of infectious disease among individuals from the general population," explained co-author Christian Medom Madsen, post-doctoral student at the varsity.However, the study cannot conclude that very low or very high HDL is the direct cause of the increased risk of infectious disease."Our findings indicate that, in the future, research into the role and function of HDL should not narrowly focus on cardiovascular disease, but rather focus on the role of HDL in other disease areas, such as infectious disease," Nordestgaard said.