Very high levels of high-density lipoprotein (HDL), the lipid that has been considered ‘good’ cholesterol, may be associated with an increased risk of heart attack and death, according to research presented at the ESC Congress.
This study, conducted as part of the Emory Cardiovascular Biobank, investigated the relationship between HDL cholesterol levels and the risk of heart attack and death in 5,965 individuals, most of whom had heart disease. The average age of participants was 63 years and 35% were female.
Participants were divided into five groups according to their HDL cholesterol level: less than 30 mg/dl (0.78 mmol/L), 31–40 mg/dl (0.8–1 mmol/L); 41–50 mg/dl (1.1–1.3 mmol/L); 51–60 mg/dl (1.3–1.5 mmol/L); and greater than 60 mg/dl (1.5 mmol/L).
During a median follow-up of four years, 769 (13%) participants had a heart attack or died from a cardiovascular cause. Participants with HDL cholesterol 41–60 mg/dl (1.1–1.5 mmol/L) had the lowest risk of heart attack or cardiovascular death. Risk was increased both in participants with low levels (less than 41 mg/dl [1.1 mmol/L]) and very high levels (greater than 60 mg/dl [1.5 mmol/L) of HDL cholesterol, which produced a U-shaped curve when plotted graphically.
Participants with HDL cholesterol levels greater than 60 mg/dl (1.5 mmol/L) had a nearly 50% increased risk of dying from a cardiovascular cause or having a heart attack compared to those with HDL cholesterol levels 41–60 mg/dl (1.1–1.5 mmol/L).
The study author Dr Marc Allard-Ratick, (Emory University School of Medicine, Atlanta, Georgia, USA) noted that more research is needed to elucidate the mechanisms of this paradoxical association. “While the answer remains unknown, one possible explanation is that extremely elevated HDL cholesterol may represent ‘dysfunctional HDL’ which may promote rather than protect against cardiovascular disease,” Dr Allard-Ratick said.
“It may be time to change the way we view HDL cholesterol. Traditionally, physicians have told their patients that the higher your ‘good’ cholesterol, the better. However, the results from this study and others suggest that this may no longer be the case”, he concluded.