A blood protein, known as surfactant protein-D (SP-D), which is mainly synthesised in the lungs, is "a good predictor" of cardiovascular disease, a new study has found.
The North America study said that the circulating SP-D levels were clearly associated with CVD and total mortality in patients with angiographically diagnosed coronary artery disease independent of other well-established risk factors.
In the lungs SP-D has a role in the body's defensive response to the many microorganisms and antigens inhaled each day, by binding to their surface and promoting their clearance from the body.
This study aimed to determine whether or not circulating SP-D is related to cardiovascular morbidity and mortality in two independent cohorts: first, a large cohort of patients having coronary angiography for suspected coronary artery disease (CAD); and second, a "replication" cohort of ex- and current smokers with mild airflow restriction but without a known history of CVD.
"We've known for a long time that chronic lung inflammation is associated with an increased risk of cardiovascular and total mortality," investigator Dr Don Sin from the Providence Heart and Lung Institute at St Paul's Hospital, and University of British Columbia, Vancouver, Canada, said.
"However, apart from lung function tests, there are no universally accepted biomarkers that could clearly predict these events.
"Recent studies have identified SP-D as a promising biomarker of lung inflammation and injury - for example, circulating SP-D levels are nearly 40 percent higher in active smokers than in lifetime non-smokers, and rise further in subjects with impaired lung function.
"It was our hypothesis that in the systemic circulation SP-D may promote atherosclerosis," Sin stated.
Sin described the association between circulating SP-D levels and CVD as "strong" but emphasised that the study was designed to determine causality.
"Based on our data, we cannot determine whether SP-D was intrinsically involved in the pathogenesis of cardiovascular events or an epiphenomenon of lung inflammation," he said.
However, he agreed that circulating SP-D levels were a strong predictor of future CVD mortality, independent of other risk factors.
The study has been published online in the European Heart Journal.