Is It Time to Stop Treating High Triglycerides?

Christopher Labos, MD CM, MSc


March 29, 2023

Recent trial evidence has failed to show a cardiovascular benefit to treating high triglycerides. The publication of the PROMINENT trial, where pemafibrate successfully lowered high levels but was not associated with a lower risk for cardiovascular events, reinforced the point. Is it time to stop measuring and treating high triglycerides?

Christopher Labos, MD CM, MSc

There may be noncardiovascular reasons to treat hypertriglyceridemia. Pancreatitis is the most cited one, given that the risk for pancreatitis increases with increasing triglyceride levels, especially in patients with a prior episode.

There may also be practical reasons to lower trigs. Because most cholesterol panels use the Friedewald equation to calculate low-density lipoprotein cholesterol (LDL-C) rather than measuring it directly, very high triglyceride levels can invalidate the calculation and return error messages on lab reports.

But we now have alternatives to measuring LDL-C, including non–high-density lipoprotein cholesterol (HDL-C) and apolipoprotein B (apoB), that better predict risk and are usable even in the setting of nonfasting samples when triglycerides are elevated.

Independent Cardiovascular Risk Factor?

If we are going to measure and treat high triglycerides for cardiovascular reasons, the relevant question is, are high triglycerides an independent risk factor for cardiovascular disease?

Proponents have a broad swath of supportive literature to point at. Multiple studies have shown an association between triglyceride levels and cardiovascular risk. The evidence even extends beyond traditional epidemiologic analyses, to genetic studies that should be free from some of the problems seen in observational cohorts.

But it is difficult to be certain whether these associations are causal or merely confounding. An unhealthy diet will increase triglycerides, as will alcohol. Patients with diabetes or metabolic syndrome have high triglycerides. So do patients with nephrotic syndrome or hypothyroidism, or hypertensive patients taking thiazide diuretics. Adjusting for these baseline factors is possible but imperfect, and residual confounding is always an issue. An analysis of the Reykjavik and the EPIC-Norfolk studies found an association between triglyceride levels and cardiovascular risk. That risk was attenuated, but not eliminated, when adjusted for traditional risk factors such as age, smoking, blood pressure, diabetes, and cholesterol.

Randomized trials of triglyceride-lowering therapies would help resolve the question of whether hypertriglyceridemia contributes to coronary disease or simply identifies high-risk patients. Early trials seemed to support the idea of a causal link. The Helsinki Heart Study randomized patients to gemfibrozil or placebo and found a 34% relative risk reduction in coronary artery disease with the fibrate. But gemfibrozil didn't only reduce triglycerides. It also increased HDL-C and lowered LDL-C relative to placebo, which may explain the observed benefit.

Gemfibrozil is rarely used today because we can achieve much greater LDL-C reductions with statins, as well as ezetimibe and PCSK9 inhibitors. The success of these drugs may not leave any room for triglyceride-lowering medications.

The Pre- vs Post-Statin Era

In the 2005 FIELD study, participants were randomized to receive fenofibrate or placebo. Although patients weren't taking statin at study entry, 17% of the placebo group started taking one during the trial. Fenofibrate wasn't associated with a reduction in the primary endpoint, a combination of coronary heart disease death or nonfatal myocardial infarction (MI). Among the many secondary endpoints, nonfatal MI was lower but cardiovascular mortality was not in the fibrate-treated patients. In the same vein, the 2010 ACCORD study randomized patients to receive simvastatin plus fenofibrate or simvastatin alone. The composite primary outcome of MI, stroke, and cardiovascular mortality was not lowered nor were any secondary outcomes with the combination therapy. In the statin era, triglyceride-lowering therapies have not shown much benefit.

The final nail in the coffin may very well be the aforementioned PROMINENT trial. The new agent, pemafibrate, fared no better than its predecessor fenofibrate. Pemafibrate had no impact on the study's primary composite outcome of nonfatal MI, stroke, coronary revascularization, or cardiovascular death despite being very effective at lowering triglycerides (by more than 25%). Patients treated with pemafibrate had increased LDL-C and apoB compared with the placebo group. When you realize that, the results of the study are not very surprising.

Some point to the results of REDUCE-IT as proof that triglycerides are still a valid target for pharmacotherapy. The debate on whether REDUCE-IT tested a good drug or a bad placebo is one for another day. The salient point for today is that the benefits of eicosapentaenoic acid (EPA) were seen regardless of either baseline or final triglyceride level. EPA may lower cardiac risk, but there is no widespread consensus that it does so by lowering triglycerides. There may be other mechanisms at work.

You could still argue that high triglycerides have value as a risk prediction tool even if their role as a target for drug therapy is questionable. There was a time when medications to lower triglycerides had a benefit. But this is the post-statin era, and that time has passed.

If you see a patient with high triglycerides, treating them with triglyceride-lowering medication probably isn't going to reduce their cardiovascular risk. Dietary interventions, encouraging exercise, and reducing alcohol consumption are better options. Not only will they lead to lower cholesterol levels, but they'll lower cardiovascular risk too.

Christopher Labos is a cardiologist with a degree in epidemiology. He spends most of his time doing things that he doesn't get paid for, like research, teaching, and podcasting. Occasionally he finds time to practice cardiology to pay the rent. He realizes that half of his research findings will be disproved in 5 years; he just doesn't know which half. He is a regular contributor to the Montreal Gazette, CJAD radio, and CTV television in Montreal and is host of the award-winning podcast The Body of Evidence.

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