High levels of circulating mannose-binding lectin (MBL) are associated with lower risk of heart attack, according to a report on page 117. The correlation is particularly strong among diabetics and people with elevated cholesterol and may be a useful indicator of future risk.

MBL is a serum protein that binds to sugar residues on a broad range of microorganisms and promotes their clearance. MBL levels have been correlated with incidence of both infectious diseases and heart disease in some studies, but others found no such link.

The current study goes a long way toward settling the heart disease controversy. “This is the first study that examines levels of MBL protein in the context of other known risk factors for myocardial infarction,” senior author Helgi Valdimarsson points out. This stratified analysis revealed a particularly strong link between MBL levels and the already increased risk of heart attack in diabetics and people with elevated cholesterol.

Measuring MBL protein levels may also be more reliable than earlier analyses of MBL genotypes. The authors find that levels of MBL protein in the blood remain virtually unchanged in an individual for decades, whereas protein levels among people with the same genotype may vary widely.

Based on unpublished in vitro binding data, the authors suggest that MBL may protect against myocardial infarction in vivo by binding to and helping clear the oxidized forms of cholesterol that build up in arteries. This type of cholesterol is abundant in diabetic patients, which may explain why high levels of MBL are particularly good news for these individuals.