An HDL cholesterol reading of 37 mg/dL falls below the threshold most medical guidelines consider protective, which is generally 40 mg/dL for men and 50 mg/dL for women. Large epidemiological studies consistently link HDL levels in this range to elevated risk of heart disease, but the relationship between HDL and health turns out to be more complicated than “higher is always better.” Understanding what a reading of 37 actually means for your body requires looking beyond the number itself.
Why Low HDL Is Tied to Heart Disease
HDL particles are often called “good cholesterol” because they carry cholesterol away from artery walls and back to the liver for disposal, a process called reverse cholesterol transport. When HDL is low, less cholesterol gets cleared from arterial tissue, which contributes to plaque buildup over time. Epidemiological data from major studies has established that HDL cholesterol is inversely related to coronary artery disease in both women and men, and that this relationship holds independently of LDL cholesterol, triglycerides, and other risk factors.1PubMed. Epidemiologic evidence for high-density lipoprotein cholesterol as a risk factor for coronary artery disease The protective effect of HDL becomes proportionately stronger as levels drop from average into the low range, meaning the difference between 37 and 50 carries more weight than the difference between 60 and 73.
A 21-year study following about 8,000 men found that those with abnormally low HDL had roughly 36 to 38 percent higher coronary heart disease mortality than men with adequate HDL, and that elevated risk persisted regardless of whether total cholesterol was high or normal.2PubMed. Isolated low HDL cholesterol as a risk factor for coronary heart disease mortality. A 21-year follow-up of 8000 men So even if your LDL and total cholesterol look fine, a reading of 37 on its own is enough to flag increased cardiovascular risk.
The Number Versus What HDL Actually Does
Here is where the story gets more interesting than a standard lab report suggests. Researchers have increasingly discovered that the amount of HDL cholesterol in your blood is a rough proxy for what really matters: how well those HDL particles function. The key job of HDL is pulling cholesterol out of cells and arterial walls, a capacity researchers measure as “cholesterol efflux capacity.” Two people can have identical HDL numbers yet very different efflux capacities, and it is the efflux that predicts heart trouble.
A large prospective study found that when researchers adjusted for efflux capacity, the association between HDL cholesterol concentration and coronary heart disease events became statistically insignificant. Meanwhile, the link between efflux capacity and heart disease held firm even after adjusting for HDL concentration.3PubMed Central. Association of HDL cholesterol efflux capacity with incident coronary heart disease events: a prospective case-control study A separate study in the New England Journal of Medicine reported that people in the highest quarter of efflux capacity had a 67 percent reduction in cardiovascular risk compared to those in the lowest quarter, in a model that already accounted for HDL cholesterol level and particle concentration.4PubMed Central. HDL Cholesterol Efflux Capacity and Incident Cardiovascular Events
What this means for someone with an HDL of 37: your number is a warning flag, but it does not tell the full story. Some people with low HDL numbers have particles that still function well, while others with “normal” HDL carry particles that are sluggish or even dysfunctional. Unfortunately, efflux capacity testing is not yet a standard clinical lab test, so the number on your lipid panel remains the practical tool doctors use.
Does Low HDL Actually Cause Heart Disease?
This question sounds academic, but it has enormous practical consequences. For years, the assumption was straightforward: low HDL causes heart disease, so raising HDL with drugs should prevent it. That assumption has not held up well.
Genetics studies delivered one of the first surprises. Researchers used a technique called Mendelian randomization, which essentially uses natural genetic variation as a stand-in for a clinical trial. In one study of over 54,000 people, carriers of a gene variant that substantially lowered their HDL cholesterol did not show the increased heart attack risk that the observational data would predict. People whose HDL was low because of this gene variant had the same heart attack risk as those without it. Meanwhile, in the general population, a comparable drop in HDL was associated with roughly double the risk.5The Journal of Clinical Endocrinology & Metabolism. LCAT, HDL Cholesterol and Ischemic Cardiovascular Disease: A Mendelian Randomization Study of HDL Cholesterol in 54,500 Individuals The implication is provocative: low HDL may be a marker that travels alongside the real causes of heart disease rather than being a direct cause itself.
Drug trials reinforced this conclusion. Multiple medications that successfully raised HDL levels failed to reduce heart attacks, strokes, or cardiovascular death when tested in randomized trials. A systematic review and meta-analysis of HDL-raising drugs found that increasing HDL through medication on top of standard lipid-lowering therapy did not produce cardiovascular benefit.6PubMed Central. Effect of HDL-Raising Drugs on Cardiovascular Outcomes: A Systematic Review and Meta-Regression A comprehensive review of evidence from both genetics and clinical trials concluded that HDL cholesterol concentrations do not appear to be a viable therapeutic target for preventing cardiovascular disease.7PubMed. HDL cholesterol concentrations and risk of atherosclerotic cardiovascular disease – Insights from randomized clinical trials and human genetics
None of this means you should ignore a reading of 37. It means the solution is probably not a pill designed to push that specific number higher. Low HDL more likely signals an underlying metabolic environment, often involving insulin resistance, excess visceral fat, or chronic inflammation, that needs addressing through broader interventions.
The U-Shaped Curve and Why Extremely High HDL Is Not Great Either
Most people hear “good cholesterol” and assume the higher the better. Population data tells a more nuanced story. Studies examining mortality across the full range of HDL values have found a U-shaped curve: both very low and very high HDL are associated with increased risk of dying.
A study using nationally representative U.S. data found that compared to people with HDL between 51 and 60 mg/dL, those with HDL at or below 30 mg/dL had about 33 percent higher all-cause mortality, while those above 70 mg/dL also had elevated risk, about 14 percent higher.8PubMed Central. The U Shaped Relationship Between High-Density Lipoprotein Cholesterol and All-Cause or Cause-Specific Mortality in Adult Population A large Chinese cohort of over 3 million people confirmed the same U-shape, with HDL below 30 mg/dL carrying about 23 percent higher all-cause mortality and HDL above 90 mg/dL carrying about 10 percent higher all-cause mortality relative to the lowest-risk range.9The Lancet Regional Health – Western Pacific. Association of high-density lipoprotein cholesterol with all-cause and cause-specific mortality in a Chinese population of 3.3 million adults: a prospective cohort study These U-shaped associations also extended to cardiovascular and cancer mortality.
At 37, you are on the left side of that U, in the zone of clearly elevated risk. But the takeaway from this research is that the goal is not to chase the highest HDL number possible. The sweet spot appears to sit in the range of roughly 50 to 70 mg/dL for most adults.
Sex Differences and Menopause
If you are a woman reading this, a 37 is especially notable. Women typically carry higher HDL than men, largely due to the effects of estrogen on lipoprotein metabolism. Compared to women, men carry significantly lower levels of the large, protective HDL subfractions.10PubMed. Effects of menopause, gender and age on lipids and high-density lipoprotein cholesterol subfractions For a man, 37 mg/dL is below the 40 mg/dL cutoff and concerning. For a woman, who would be expected to have higher levels, 37 is further below the 50 mg/dL threshold used in female-specific guidelines and represents a bigger relative deficit.
Menopause shifts the picture dramatically. Postmenopausal women show a drop in large HDL particles, an increase in LDL and oxidized LDL, and a generally more heart-disease-prone lipid profile compared to premenopausal women.11PubMed Central. Markers of increased cardiovascular risk in postmenopausal women: focus on oxidized-LDL and HDL subpopulations Menopause and male sex are both associated with decreased cholesterol content within HDL particles.12PubMed. Effects of gender, age and menopausal status on serum apolipoprotein concentrations So a postmenopausal woman discovering an HDL of 37 should view it in the context of these hormonal shifts and discuss cardiovascular risk assessment with her doctor.
Low HDL, Diabetes Risk, and Brain Health
Cardiovascular disease gets most of the attention, but a low HDL reading connects to other health outcomes worth knowing about. One is type 2 diabetes. A large population-based study found that people with persistently low mean HDL had about 35 percent higher risk of developing diabetes compared to those with high, stable HDL. When low HDL was combined with high variability in HDL over time, the risk was about 40 percent higher.13The Journal of Clinical Endocrinology & Metabolism. HDL-Cholesterol, Its Variability, and the Risk of Diabetes: A Nationwide Population-Based Study Another study found that each standard-deviation increase in HDL was associated with substantially lower odds of developing type 2 diabetes, independent of body weight, blood pressure, and other risk factors.14The Journal of Clinical Endocrinology & Metabolism. Role of HDL Cholesterol and Estimates of HDL Particle Composition in Future Development of Type 2 Diabetes in the General Population: The PREVEND Study
Cognitive health is another area of concern. A study that followed participants for 19 years after measuring their midlife HDL found that those in the highest HDL quartile had less than half the risk of mild cognitive impairment in later life compared to those with very low HDL. Higher HDL at midlife was also linked to significantly lower risk of dementia.15Translational Psychiatry. The association between midlife serum high-density lipoprotein and mild cognitive impairment and dementia after 19 years of follow-up An Italian study of elderly participants confirmed this relationship, finding that lower HDL was associated with dementia even after controlling for age, sex, genetic risk factors, stroke, and inflammatory markers.16The Journals of Gerontology: Series A. Relationship Between Low Levels of High-Density Lipoprotein Cholesterol and Dementia in the Elderly. The InChianti Study It is worth noting that these are observational associations, not proof of causation, but the pattern is consistent and gives another reason to address low HDL.
Lifestyle Changes That Can Move the Number
Since HDL-raising drugs have not panned out, lifestyle interventions carry even more weight. Regular aerobic exercise is one of the most reliable ways to raise HDL levels. Reviews and meta-analyses consistently show that physical activity increases HDL cholesterol while lowering LDL and triglycerides.17PubMed Central. The Impact of Aerobic Exercise on HDL Quantity and Quality: A Narrative Review Exercise does not just push the number up; it also improves HDL particle composition and functionality, making the particles better at their job. That said, the evidence suggests there may be a dose threshold you need to cross before seeing meaningful improvements in efflux capacity, so casual walking alone may not be enough.18PubMed Central. Effects of exercise on HDL functionality
Quitting smoking, if relevant, produces one of the fastest HDL improvements available. A review of studies tracking within-person changes found that HDL rises within three weeks of quitting smoking, with no clear pattern of further change after that initial bump.19PubMed Central. The effect of quitting smoking on HDL-cholesterol – a review based on within-subject changes One study in female smokers found that HDL increased by about 6 mg/dL within 30 days of quitting and by another 7 mg/dL by day 60. Those who resumed smoking saw their HDL drop back to pre-cessation levels.20Atherosclerosis. Effects of cessation of smoking on serum lipids and high density lipoprotein-cholesterol For someone starting at 37 mg/dL, a gain of 6 to 13 points from quitting smoking alone could push you past the 40 mg/dL threshold or even further.
Diet plays a meaningful role as well. A Mediterranean-style diet, rich in olive oil, nuts, fish, and vegetables, has been shown to improve HDL function beyond what the raw number might reflect. In a randomized controlled trial, a traditional Mediterranean diet supplemented with virgin olive oil improved cholesterol efflux capacity, enhanced the antioxidant properties of HDL particles, and increased the proportion of large HDL particles.21PubMed. Mediterranean Diet Improves High-Density Lipoprotein Function in High-Cardiovascular-Risk Individuals: A Randomized Controlled Trial A systematic review confirmed that this eating pattern’s benefits extend to reducing HDL oxidation and improving overall HDL quality.22PubMed Central. High-Density Lipoproteins and Mediterranean Diet: A Systematic Review Interestingly, a head-to-head comparison of Mediterranean and vegetarian diets found that participants on the vegetarian diet showed a significant reduction in HDL’s efflux capacity, while those on the Mediterranean diet maintained it better.23PubMed. Effects of a dietary intervention with Mediterranean vs lacto-ovo vegetarian diets on HDL function: Results from the CARDIVEG study
When HDL Becomes Dysfunctional
Beyond the question of how much HDL you have, there are conditions where HDL particles actively go wrong. In autoimmune diseases like lupus and rheumatoid arthritis, a significant portion of HDL particles become “pro-inflammatory,” meaning they promote arterial damage rather than prevent it. In one study, roughly 45 percent of lupus patients and 20 percent of rheumatoid arthritis patients had pro-inflammatory HDL, compared to only about 4 percent of healthy controls. Lupus patients with coronary artery disease had significantly higher pro-inflammatory HDL scores than those without it.24PubMed. Proinflammatory high-density lipoprotein as a biomarker for atherosclerosis in patients with systemic lupus erythematosus and rheumatoid arthritis A follow-up study in women with lupus confirmed these findings and showed that those with pro-inflammatory HDL had more arterial plaque and thicker artery walls.25PubMed Central. Dysfunctional Pro-Inflammatory High Density Lipoproteins Confer Increased Risk for Atherosclerosis in Women with Systemic Lupus Erythematosus
HDL also plays a role in immune defense that most people do not hear about. Recent research has shown that HDL particles can dampen inflammatory responses to bacterial toxins by degrading them through a specific receptor pathway. In animal experiments, boosting HDL levels reduced inflammation-driven organ damage and improved survival during severe infection.26PubMed Central. High-density lipoprotein attenuates lipopolysaccharide-induced IL-1β activation via scavenger receptor class B type 1 This is early-stage science, but it suggests that low HDL may compromise your immune system’s ability to manage inflammation, adding yet another dimension to what a reading of 37 might mean for overall health.
Rare Genetic Causes of Very Low HDL
Most cases of low HDL are driven by lifestyle factors, metabolic syndrome, or medications. But in rare instances, extremely low HDL has a genetic origin. Tangier disease is an inherited condition caused by mutations in the ABCA1 gene, which is essential for building HDL particles from cellular cholesterol. People with Tangier disease have near-absent HDL cholesterol and accumulate cholesterol in tissues throughout the body.27PubMed Central. Current Diagnosis and Management of Tangier Disease The disease follows an autosomal recessive inheritance pattern, meaning you need defective copies from both parents to develop the full condition.28PubMed. Tangier disease and ABCA1 Carriers of a single defective copy can have moderately reduced HDL without the full syndrome.
If your HDL has been persistently very low despite a healthy lifestyle and no obvious metabolic explanation, and particularly if you have a family history of extremely low HDL, it is worth discussing genetic testing with your doctor. But for the vast majority of people seeing 37 on a lab report, the causes are modifiable.
The Shift Toward Non-HDL Cholesterol in Clinical Practice
Given the muddied picture around HDL, clinical guidelines have been quietly evolving. Rather than trying to push HDL higher, many international guidelines now emphasize non-HDL cholesterol (your total cholesterol minus your HDL) and apolipoprotein B as better targets for managing heart disease risk. Non-HDL cholesterol captures all the potentially harmful lipoprotein particles in a single number and is recommended as a secondary treatment goal for managing abnormal lipid levels by most major guidelines.29PubMed. Non-HDL-cholesterol in dyslipidemia: Review of the state-of-the-art literature and outlook Some guidelines are moving toward treating apolipoprotein B as an even more reliable marker, particularly in people with complex lipid disorders.30PubMed Central. The Role of Non-HDL Cholesterol and Apolipoprotein B in Cardiovascular Disease: A Comprehensive Review
What this means for you: if your HDL is 37, your doctor will likely focus treatment on lowering your LDL, non-HDL cholesterol, or apolipoprotein B rather than specifically trying to raise your HDL through medication. The interventions that happen to raise HDL, like exercise, dietary changes, weight loss, and quitting smoking, are still recommended, but they are recommended because they improve your overall metabolic health, not because bumping HDL from 37 to 45 is the primary goal.
Measuring HDL Is Harder Than It Looks
One wrinkle worth knowing about: the standard HDL-C test on a basic lipid panel measures the total cholesterol carried by all HDL particles combined. It tells you nothing about how many particles you have, how large they are, or how well they function. Advanced tests exist that break HDL into subclasses by size and density, but these methods do not always agree with each other. A comparison of five different HDL particle measurement techniques found substantial discordance, particularly at lower HDL levels. In the lowest third of HDL-C, one method found 8 percent large HDL particles while others found 18 to 22 percent.31Clinical Chemistry. HDL Particle Measurement: Comparison of 5 Methods One commonly used commercial method based on NMR spectroscopy has been criticized for generating particle stoichiometries that are inconsistent with established biochemistry.32PubMed Central. Quantification of HDL particle number (HDL-P) by proton NMR: Don’t believe the numbers
For most people, the standard HDL-C number on a routine lipid panel is the clinically actionable measurement. Advanced particle testing can provide additional information in complex cases, but the field has not settled on a gold standard, and the results are not always clinically actionable. If your doctor orders advanced lipid testing, ask specifically how the results would change your treatment plan before investing too much weight in the subclass details.