High levels of triglyceride molecules in LDL cholesterol are “robustly” linked with an increased risk of atherosclerotic cardiovascular disease, according to a study that used two different methods in two separate cohorts from a large European population study plus a meta-analysis to verify the results.
“There have been some studies in the past, as you can see from our meta-analysis, that found a similar association, but I don’t think most people are convinced that there is really this relationship, and certainly I was not convinced,” lead investigator Børge G. Nordestgaard, MD, DMSc, professor at the University of Copenhagen, said in an interview.
Dr. Børge G. Nordestgaard
The study enrolled 68,290 patients from the Copenhagen General Population study; 38,081 were assigned to direct automated assay to measure their LDL triglycerides and 30,208 had nuclear magnetic resonance (NMR) spectroscopy. Median follow-up was 3 and 9.2 years for the respective cohorts.
LDL triglycerides carry higher ASCVD risk
In the automated assay group, each 0.1-mmol/L (9 mg/dL)–higher direct LDL triglycerides carried a 22%-38% higher risk for the following outcomes: ASCVD (hazard ratio, 1.26; 95% confidence interval, 1.17-1.35); ischemic heart disease (HR, 1.27; 95% CI, 1.16-1.39); myocardial infarction (HR, 1.28; 95% CI, 1.11-1.48); ischemic stroke (HR, 1.22; 95% CI, 1.08-1.38); and peripheral artery disease (HR, 1.38; 95% CI, 1.21-1.58).
In the group that had NMR spectroscopy to measure LDL triglycerides, risks were similar, ranging from HRs of 1.13 (95% CI, 1.05-1.23) for ischemic stroke to 1.41 (95% CI, 1.31-1.52) for myocardial infarction. The investigators noted that apolipoprotein B levels didn’t entirely explain these results.
The meta-analysis included 18 studies that evaluated varying cardiovascular disease outcomes. It compared random-effects risk ratios for the highest quartile vs. the lowest quartile of LDL triglycerides. They were 1.50 (95% CI, 1.35-1.66) for ASCVD (four studies, 71,526 individuals, 8,576 events); 1.62 (95% CI, 1.37-1.93) for ischemic heart disease (six studies, 107,538 individuals, 9,734 events); 1.30 (95% CI, 1.13-1.49) for ischemic stroke (four studies, 78,026 individuals, 4,273 events); and 1.53 (95% CI, 1.29-1.81) for peripheral artery disease (four studies, 107,511 individuals, 1,848 events). The study was published online in the Journal of the American College of Cardiology.
Results confirm hypothesis the study sought to disprove
The purpose of the study was to actually disprove the hypothesis that the study ended up confirming, Dr. Nordestgaard said. “When we started this study, my idea was that we wanted to show that LDL triglyceride was not related to these diseases, because that didn’t make sense to me,” he said. “I’m so used to the thinking that the cholesterol content of these particles drive atherosclerosis and therefore atherosclerotic cardiovascular disease.”
He noted that LDL can carry both cholesterol and triglycerides, and that larger remnant lipoproteins can carry a substantial amount of triglycerides and a lesser amount of cholesterol. “Those remnants actually transfer into LDL, so they somewhat bring the triglycerides molecules into LDL,” Dr. Nordestgaard said.
The direct automated assay test used in the study to measure LDL triglycerides is not approved for use in the United States by the Food and Drug Administration, according to Denka, the manufacturer of the test.
The use of the Copenhagen General Population Study cohorts is a strength of the study because it has 100% follow-up with all patients, Dr. Nordestgaard said. The meta-analysis is another strength. “So we can show real clearly, not only in our two prospective studies, but also added to the former ones in the literature: All say exactly the same thing: High LDL triglycerides carry a high risk for ASCVD and its components.”
A limitation Dr. Nordestgaard acknowledged: The study doesn’t explain the causal relationship between high LDL triglycerides and ASCVD. But the study provides “very sound evidence that there’s a relationship,” he added. The study population was also a White, Danish population that lacked ethnic and racial diversity.