High and Low Levels of HDL Cholesterol Increase Risk of Infectious Disease

HDL cholesterol is known as the good kind, but too much or too little could negatively impact the immune system.

High-density lipoprotein (HDL) cholesterol—the so called “good” kind—plays an important role in maintaining a healthy immune system. HDL cholesterol can have a not-so-good impact on immunity, however, if levels are too high or too low, according to a study published in European Heart Journal.

According to the findings, patients with high and low levels of HDL cholesterol had a higher risk of being hospitalized for an infectious disease and a higher chance of these diseases becoming fatal.

"Surprisingly, we found that individuals with both low and high HDL cholesterol had high risk of hospitalization with an infectious disease,” Børge Nordestgaard, MD, DMSc, lead author, said in a press release. “Perhaps more importantly, these same groups of individuals had high risk of dying from infectious disease.”

To conduct the study, researchers examined data from 100,000 people who were followed for more than 6 years.

The findings showed that 21% of the population with the lowest HDL levels and 8% of the population with the highest HDL levels were at a higher risk of infectious diseases, such as gastroenteritis or pneumonia, than those with normal HDL levels.

Those with low HDL levels had a 75% greater risk of infectious disease compared with the reference group, and those with high HDL levels had a 43% greater risk of infectious disease, according to the researchers.

The authors highlighted the important role HDL plays in immune system function.

"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, but this study is the first to examine if HDL is associated with the risk of infectious disease among individuals from the general population," Christian Medom Madsen, MD, coauthor, and PhD student, said in the press release.

Although data from the genetic portion of the study may indicate a direct link between high or low HDL levels and the risk of infectious disease, the authors cannot identify HDL level as a direct cause of infectious diseases, according to the study.

The authors noted that the relationship between HDL level and the risk of infectious disease prompts further investigation.

"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," Dr Nordestgaard said in the press release.

References

Madsen CM, Varbo A, Tybjærg-Hansen A, et al. U-shaped relationship of HDL and risk of infectious disease: two prospective population-based cohort studies. European Heart Journal. 2018;39 (14): 1181 DOI: 10.1093/eurheartj/ehx665

Higher risk of infectious disease with both high and low cholesterol [news release]. University of Copenhagen’s website. http://healthsciences.ku.dk/news/2018/04/higher-risk-of-infectious-disease-with-both-high-and-low-cholesterol/. Accessed April 13, 2018.