- HDL helps carry extra cholesterol from the body back to the liver. Low HDL is under 40 mg/dL in men and under 50 mg/dL in women.
- Low HDL is often a sign of insulin resistance, along with high triglycerides and belly fat, rather than a cause of heart disease on its own.
- Medicines that pushed HDL up by as much as 130% did not prevent heart attacks.
- Very high HDL is not extra protective: in Danish studies, the lowest death rates were at moderate levels.
HDL has a great reputation. It is the “good” cholesterol, and for decades the advice was simple: the higher, the better. That idea made sense from early studies, and it is still partly true. But large trials and genetic research over the last 15 years have changed the picture. HDL turns out to be more of a messenger about your metabolic health than a shield you can simply turn up.
This article explains what HDL does, what your number is really telling you and how to improve the things that low HDL points to. For all the ranges on a lipid panel, see understanding cholesterol numbers.
What HDL does
HDL stands for high-density lipoprotein. HDL particles are small, protein-rich carriers made mainly by the liver and gut. Their best-known job is reverse cholesterol transport: picking up surplus cholesterol from tissues, including immune cells in artery walls, and bringing it back to the liver to be reused or removed in bile.
Reverse cholesterol transport, simplified
The HDL cholesterol test measures how much cholesterol HDL carries, not how well it does this job.
That last point is the key. Your HDL number tells you how much cholesterol is sitting inside HDL particles at one moment. It does not tell you how well those particles are working. Two people with the same HDL level can have very different HDL function.
What low HDL is really telling you
In large population studies, people with higher HDL do have fewer heart attacks. An analysis of 68 studies with over 300,000 people found about 22% lower heart disease risk for each step up in HDL of roughly 15 mg/dL. But people with low HDL also tend to have other things going on.
Fat around the organs is linked with lower HDL. See visceral fat and metabolic health.
When triglyceride-rich particles are high, HDL tends to fall. The two usually move in opposite directions.
Low HDL is one of the five markers of metabolic syndrome and is common in prediabetes and type 2 diabetes.
Both lower HDL and raise heart risk in many other ways.
So low HDL is often a flag for insulin resistance and the metabolic syndrome. Low HDL is also common in South Asians, often alongside high triglycerides, even at a normal body weight. The number is valuable as a warning light. The question researchers asked next was whether pushing the number up would help.
Raising HDL with drugs did not help
If HDL protected the heart directly, then raising it should prevent heart attacks. Several very large trials tested exactly that. The results were consistently disappointing.
A CETP inhibitor raised HDL by about 72%, but deaths and heart events went up, partly from raised blood pressure. The trial was stopped early.
In 3,414 people already on statins, niacin raised HDL from about 35 to 42 mg/dL. There was no reduction in heart events, and the trial was stopped early.
In about 25,700 high-risk patients, extended-release niacin did not reduce major events and increased serious side effects, including infections, bleeding and diabetes problems.
HDL more than doubled (up about 130%), yet there was no benefit at all on heart attacks, strokes or deaths.
ILLUMINATE, NEJM 2007; AIM-HIGH, NEJM 2011; HPS2-THRIVE, NEJM 2014; ACCELERATE, NEJM 2017.
Genetic studies agree. People born with gene variants that raise HDL alone, without changing LDL or triglycerides, do not have fewer heart attacks. In a 2012 study of about 20,000 heart attack cases, one such variant raised HDL but did not lower heart attack risk. Together, this suggests HDL cholesterol is mostly a marker, not a cause.
Can HDL be too high?
Surprisingly, yes. Two large Danish studies followed about 116,000 adults for around six years. Very high HDL was linked with higher, not lower, death rates.
HDL and risk of death in two Danish cohorts
Madsen et al., Eur Heart J 2017 (Copenhagen City Heart Study and Copenhagen General Population Study). Low HDL was also linked with higher risk, giving a U-shaped curve.
This is an observational finding, so it does not prove high HDL causes harm. Very high HDL can go along with heavy alcohol use, some genetic variants and other conditions. The practical message: a very high HDL is not a reason to ignore a high LDL.
What to do about low HDL
Because low HDL is usually a sign of wider metabolic strain, the aim is not to chase the number but to fix what is behind it. The good news: the same habits that improve insulin resistance also tend to nudge HDL up and triglycerides down.
- Move most days. Regular aerobic exercise tends to raise HDL modestly, by a few mg/dL. Brisk walking counts.
- Lose some weight if you carry extra, especially around the waist.
- Cut refined carbs and sugar. Fewer sweets, sugary drinks, maida and large rice portions help lower triglycerides.
- Choose healthy fats. Nuts, seeds, olive, mustard or groundnut oil instead of vanaspati and trans fats.
- Stop smoking. Quitting raises HDL and lowers heart risk far beyond that.
Check your waist. Our Waist-to-Height Ratio Calculator gives a quick sense of belly fat, which is closely tied to low HDL.
Do not take niacin or other supplements to raise HDL unless your doctor advises it. High-dose niacin can cause flushing, liver problems and higher blood sugar, and trials show no heart benefit on top of a statin.
MythA high HDL cancels out a high LDL.
FactIt does not. LDL and apoB drive plaque. Your doctor judges risk mainly on LDL, blood pressure, blood sugar, smoking and age, whatever your HDL.
Common questions
Is the total-to-HDL ratio useful?
It adds a little information and is used in some risk calculators. But treatment targets focus on LDL, non-HDL cholesterol or apoB.
Does alcohol raise HDL?
Alcohol can raise HDL, but that does not translate into heart protection, and alcohol raises triglycerides, blood pressure and liver fat. It is not a reason to drink.
My HDL is 38 but everything else is normal. Should I worry?
It is worth checking fasting glucose or HbA1c, triglycerides and waist size, since low HDL often travels with insulin resistance. Talk to your doctor about your overall risk.
- HDL helps return cholesterol to the liver, but the test does not measure how well it works.
- Low HDL is mainly a warning sign of insulin resistance and metabolic syndrome.
- Drugs that raised HDL did not reduce heart attacks; LDL remains the main target.
- Very high HDL is not extra protective; activity, weight loss and not smoking help most.
- Next: Triglycerides: What Raises Them and How to Lower Them.
Sources
- Emerging Risk Factors Collaboration. Major lipids, apolipoproteins, and risk of vascular disease. JAMA. 2009;302(18):1993–2000.
- AIM-HIGH Investigators. Niacin in patients with low HDL cholesterol levels receiving intensive statin therapy. N Engl J Med. 2011;365(24):2255–2267.
- HPS2-THRIVE Collaborative Group. Effects of extended-release niacin with laropiprant in high-risk patients. N Engl J Med. 2014;371(3):203–212.
- Barter PJ, Caulfield M, Eriksson M, et al. Effects of torcetrapib in patients at high risk for coronary events. N Engl J Med. 2007;357(21):2109–2122.
- Lincoff AM, Nicholls SJ, Riesmeyer JS, et al. Evacetrapib and cardiovascular outcomes in high-risk vascular disease. N Engl J Med. 2017;376(20):1933–1942.
- Voight BF, Peloso GM, Orho-Melander M, et al. Plasma HDL cholesterol and risk of myocardial infarction: a mendelian randomisation study. Lancet. 2012;380(9841):572–580.
- Madsen CM, Varbo A, Nordestgaard BG. Extreme high high-density lipoprotein cholesterol is paradoxically associated with high mortality in men and women: two prospective cohort studies. Eur Heart J. 2017;38(32):2478–2486.
- Mach F, Baigent C, Catapano AL, et al. 2019 ESC/EAS Guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk. Eur Heart J. 2020;41(1):111–188.
This article is for general education and is not a substitute for advice from your own doctor or healthcare team.