- 01Low HDL points to a cause; ApoB measures the risk
Low HDL predicts heart disease in population studies, but raising HDL with niacin or by gene variants did not prevent heart attacks. Treat a low HDL as a pointer to its cause (usually insulin resistance, inactivity or smoking) and judge risk by ApoB, blood pressure and blood sugar.
Most low HDL results trace back to a short list: high triglycerides with insulin resistance, extra weight around the middle, too little exercise, smoking, or a medicine. HDL works best as a clue to those causes, and the changes that lift HDL a few points are the same ones linked to lower heart risk, mostly through their effect on triglycerides, ApoB, blood pressure and blood sugar.
What counts as low HDL
HDL cholesterol is the cholesterol carried inside high-density lipoproteins, the small particles that ferry cholesterol from tissues back to the liver. US cholesterol guidelines treat an HDL below 40 mg/dL as a risk factor in anyone, and count 60 mg/dL and up as protective 9. The American Heart Association's definition of metabolic syndrome sets the line higher for women: below 40 mg/dL (1.0 mmol/L) in men and below 50 mg/dL (1.3 mmol/L) in women 1. Women usually run higher than men, largely because of estrogen, which is why the same 45 mg/dL reads as fine for a man and low for a woman.
Where an example HDL of 38 mg/dL fallsmg/dL
| Band | Men | Women | mmol/L (men / women) |
|---|---|---|---|
| Very low | Below 20 mg/dL | Below 20 mg/dL | Below 0.5 |
| Low | 20 to 39 mg/dL | 20 to 49 mg/dL | 0.5 to 1.0 / 0.5 to 1.3 |
| Typical | 40 to 59 mg/dL | 50 to 59 mg/dL | 1.0 to 1.5 / 1.3 to 1.5 |
| High | 60 mg/dL and up | 60 mg/dL and up | 1.55 and up |
CalculatorCholesterol converterGot HDL in mmol/L? Convert it to mg/dL (or back) before you compare it with the lines above.Work it out A result of 37, 38 or 39 mg/dL sits close enough to the 40 line that ordinary variation between tests can move it across. HDL drifts by a few mg/dL between draws with season, recent exercise, alcohol and illness, so one reading of 39 and a later one of 42 are close to the same result. See why a trend beats a single reading before acting on one number. The parent HDL cholesterol page covers the marker in full, including what a high HDL means.
Why is my HDL low? The common causes
What lowers HDL? Most often insulin resistance, where the body needs more insulin than usual to move glucose into cells. Insulin resistance raises triglycerides, and the extra triglyceride gets swapped into HDL particles in place of their cholesterol. Those particles are cleared faster, so the HDL number falls. That is why low HDL and high triglycerides so often arrive together, and why both are part of metabolic syndrome.
How insulin resistance pulls HDL down
| Cause | What usually goes with it on the panel |
|---|---|
| Insulin resistance, extra belly fat | Triglycerides above 150 mg/dL, higher fasting glucose or HbA1c, higher fasting insulin |
| Little or no exercise | Often nothing else; HDL is low on its own |
| Smoking | LDL often unchanged; HDL lower than expected for weight and diet |
| Diet high in refined carbs or trans fat | Higher triglycerides; trans fat also raises LDL |
| Genetics and sex | Low HDL in parents or siblings; men run lower than women |
| Overactive thyroid | Low TSH, often low total cholesterol too (an underactive thyroid mainly raises LDL instead) |
| Recent infection, surgery or inflammation | Raised CRP; HDL rebounds weeks after recovery |
| Kidney or liver disease | Abnormal eGFR, creatinine or liver enzymes |
Medicines are the other big group. Anabolic steroids and high-dose testosterone can cut HDL sharply, sometimes by more than half, which makes them a leading cause of very low HDL in otherwise healthy young men. Progestins, older beta-blockers such as atenolol and propranolol, some retinoids used for acne, and certain HIV medicines lower HDL too. Menopause can drop HDL a little as estrogen falls. If a low HDL appeared after starting a medicine, raise the timing with whoever prescribed it rather than stopping the medicine on your own.
When very low HDL needs a closer look
Most very low results have an ordinary explanation: steroid use, triglycerides in the thousands, a test taken during a severe illness, or a lab artefact that a repeat test clears up. When none of those fit, a clinician may look for rare inherited conditions. Tangier disease (a fault in the ABCA1 gene) leaves HDL close to zero and gives the orange tonsils. LCAT deficiency causes cloudy corneas and can affect the kidneys. Some ApoA-I gene variants lower HDL sharply. These are rare, and an apolipoprotein A1 level is usually the first test that narrows them down.
Reading low HDL with the rest of your panel
A low HDL means different things depending on the numbers beside it. Three patterns cover most panels.
- Low HDL with high triglycerides: the insulin resistance pattern. The triglyceride/HDL ratio, fasting insulin and HbA1c show how far it has gone; see insulin resistance.
- Low HDL with normal LDL: LDL can look fine while the number of plaque-forming particles is high. ApoB or non-HDL cholesterol gives the truer count; the ApoB vs LDL comparison explains why.
- Low total cholesterol with low HDL: common on a statin, on a lean or vegan diet, with an overactive thyroid, or after a recent illness. If none of those apply, it is worth asking about.
| Worked example | HDL 38, triglycerides 220 mg/dL | HDL 38, triglycerides 70 mg/dL |
|---|---|---|
| Triglyceride/HDL ratio | 5.8 (high) | 1.8 (low) |
| Most likely reading | Insulin resistance pattern | Inherited low HDL, inactivity or smoking |
| Worth checking next | Fasting glucose or HbA1c, fasting insulin, waist, ApoB | ApoB, smoking status, family history |
| Where the risk sits | Higher: the low HDL travels with other risk | Often lower, if ApoB and blood pressure are normal |
Want the ratios for your own numbers? The cholesterol ratio calculator works out triglyceride/HDL, total/HDL and non-HDL in one step.
Markers to read beside a low HDL
Is low HDL dangerous?
Low HDL predicts heart disease in population studies. The Emerging Risk Factors Collaboration pooled 302,430 people and found that each 15 mg/dL higher HDL went with about 22% lower coronary heart disease risk after adjusting for other factors 2. In the TNT trial, even among people on statins with LDL below 70 mg/dL, those with the lowest HDL still had more heart events 10.
The link does not hold up when HDL is raised on purpose. People born with a gene variant that naturally lifts HDL have no fewer heart attacks than people without it 3. In the AIM-HIGH trial, adding niacin to a statin raised HDL and still did not prevent events 4.
Among patients with atherosclerotic cardiovascular disease and LDL cholesterol levels of less than 70 mg per deciliter (1.81 mmol per liter), there was no incremental clinical benefit from the addition of niacin to statin therapy during a 36-month follow-up period, despite significant improvements in HDL cholesterol and triglyceride levels.AIM-HIGH Investigators, New England Journal of Medicine, 2011 4
The larger HPS2-THRIVE trial, in 25,673 people, found the same lack of benefit from niacin (combined with a flushing blocker), and more serious side effects, including bleeding, infections and new diabetes 5. Taken together, these results suggest low HDL marks risk that comes from somewhere else, and raising HDL on its own does not lower that risk. HDL still counts in the US 10-year risk calculators and in the total cholesterol/HDL ratio, so a low HDL does push a risk estimate up.
Your cholesterol ratios, in context
Two ratios that say more than any single number. Nothing leaves your browser.
How to raise HDL, and what else the same changes do
The changes that lift HDL move it by a few mg/dL. Their value is that they also lower triglycerides, ApoB, blood pressure and blood sugar, which is where the heart benefit comes from. Regular aerobic exercise has the best-measured effect, with roughly 120 minutes a week as the least that showed a rise 6. Weight loss lifts HDL once weight has settled, though HDL can dip during active weight loss before it rises 7. Quitting smoking raised HDL within a year in a randomised trial 8.
| Change | Typical HDL shift | What else it moves |
|---|---|---|
| Aerobic exercise, about 120+ minutes a week | About +2.5 mg/dL 6 | Lower triglycerides, blood pressure and glucose |
| Weight loss, once weight is stable | About +0.35 mg/dL per kg lost 7 | Lower triglycerides, insulin and blood pressure |
| Quitting smoking | About +2.4 mg/dL in one year 8 | Large drop in heart attack and cancer risk |
| Swap refined carbs and trans fat for unsaturated fats | Small rise | Lower triglycerides; trans fat removal also lowers LDL |
Do supplements or medicines raise HDL?
Niacin raises HDL more than any other over-the-counter product, and it is the one with the clearest trial evidence of no heart benefit and added harm 4 5. CETP inhibitors, a drug class built to raise HDL, raised it sharply but did not deliver matching heart benefit. Fibrates raise HDL a little and mainly lower triglycerides. Statins raise HDL by a few percent, but their benefit comes from lowering LDL and ApoB. Omega-3 fats mainly lower triglycerides and have a small effect on HDL. No supplement fixes a low HDL, and none should be started for HDL alone without talking it through with a clinician.
What the evidence says about compounds people try for low HDL
Retesting and what to check next
Give a change 8 to 12 weeks before retesting HDL, and use the same lab and similar conditions each time. HDL barely changes after a normal meal, so fasting is not essential for it. Avoid testing during or within a few weeks of an infection, surgery or other acute illness, because inflammation pulls HDL down for a while. Useful next tests are ApoB, lipoprotein(a) (inherited and measured once in a lifetime for most people), hs-CRP (a sensitive inflammation test) and TSH (the main thyroid test). A low TSH fits an overactive thyroid, which can pull HDL down; a high TSH points to hypothyroidism, which mainly raises LDL and total cholesterol.
For the rest of the panel, the guide on how to read your lipid panel walks through each line, and the heart topic gathers the other cardiovascular markers in one place.
Citations
- Grundy SM et al. Diagnosis and management of the metabolic syndrome: an AHA/NHLBI scientific statement. Circulation 2005;112:2735-52.
- Emerging Risk Factors Collaboration. Major lipids, apolipoproteins, and risk of vascular disease. JAMA 2009;302:1993-2000.
- Voight BF et al. Plasma HDL cholesterol and risk of myocardial infarction: a mendelian randomisation study. Lancet 2012;380:572-80.
- AIM-HIGH Investigators. Niacin in patients with low HDL cholesterol levels receiving intensive statin therapy. N Engl J Med 2011;365:2255-67.
- HPS2-THRIVE Collaborative Group. Effects of extended-release niacin with laropiprant in high-risk patients. N Engl J Med 2014;371:203-12.
- Kodama S et al. Effect of aerobic exercise training on serum levels of high-density lipoprotein cholesterol: a meta-analysis. Arch Intern Med 2007;167:999-1008.
- Dattilo AM, Kris-Etherton PM. Effects of weight reduction on blood lipids and lipoproteins: a meta-analysis. Am J Clin Nutr 1992;56:320-8.
- Gepner AD et al. Effects of smoking and smoking cessation on lipids and lipoproteins: outcomes from a randomized clinical trial. Am Heart J 2011;161:145-51.
- National Cholesterol Education Program Expert Panel. Executive summary of the third report of the NCEP Expert Panel (Adult Treatment Panel III). JAMA 2001;285:2486-97.
- Barter P et al. HDL cholesterol, very low levels of LDL cholesterol, and cardiovascular events. N Engl J Med 2007;357:1301-10.
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
