Body mass index and the risk of infection - from underweight to obesity.

BACKGROUND: Nutritional status is a well-known risk factor for metabolic and endocrine disorders. Recent studies suggest that dietary intake also affects immune function and as a consequence infection risk. AIMS: This reviews aims to give an overview on the effect of body weight on infection rate at different periods of life. SOURCES: Clinically relevant prospective, cross-sectional and case-control community-based studies are summarized. CONTENT: In children and adolescents underweight is a significant risk factor for infection especially in developing countries, probably reflecting malnutrition and poor hygienic standards. Data from industrialized countries suggest that infection rate is also increased in obese children and adolescents. Similarly, several studies suggest a U-shaped increased infection rate in both underweight and obese adults. In the latter, infections of the skin and respiratory tract as well as surgical-site infections have consistently been reported to be more common than in normal-weight participants. Paradoxically, mortality of critically ill patients was reduced in obesity in some studies. IMPLICATIONS: Several studies in children or adults suggest that both underweight and obesity are associated with increased infection risk. However, confounding factors such as malnutrition, hygienic status and underlying disease or co-morbidities might aggravate accurate assessment of the impact of body weight on infection risk.