Low HDL cholesterol results from a combination of lifestyle habits, metabolic conditions, genetics, and inflammation. HDL is considered low below 40 mg/dL for men and below 50 mg/dL for women. About 14% of U.S. adults have low HDL, with men affected more than three times as often as women (21.5% versus 6.6%).
How HDL Works in Your Body
HDL particles act like cholesterol recyclers. They pick up excess cholesterol from your arteries and cells, then carry it back to the liver for disposal. This cleanup process is what gives HDL its reputation as “good” cholesterol. Anything that disrupts the formation, loading, or survival of these particles in your bloodstream can lower your HDL level.
The process starts with a protein scaffold that grabs fats from cell surfaces, wraps around them, and forms a disc-shaped particle. That particle then circulates through your blood, collecting more cholesterol as it goes. If your body can’t build these particles properly, or breaks them down too fast, your HDL drops.
Smoking
Cigarette smoking lowers HDL through multiple routes. It interferes with the enzymes your body uses to load cholesterol onto HDL particles, disrupting the normal assembly line. Smoking also causes oxidative damage to existing HDL particles, essentially breaking them so they can no longer do their job. Even structurally intact HDL in smokers loses its protective properties, meaning the particles that remain in circulation are less effective at clearing cholesterol from arteries.
Insulin Resistance and High Triglycerides
High triglycerides and low HDL almost always travel together. When your triglyceride levels are elevated, your body produces large, fat-heavy particles that interact with HDL in a way that destabilizes it. The HDL particles become enriched with triglycerides instead of cholesterol, which makes them smaller and easier for the kidneys and liver to break down and clear from the blood. The result is accelerated HDL destruction.
Insulin resistance drives this cycle. When your cells respond poorly to insulin, your liver ramps up production of triglyceride-rich particles, which in turn speeds up HDL breakdown. This is why low HDL is a hallmark of metabolic syndrome, the cluster of risk factors that includes high blood sugar, excess belly fat, high blood pressure, and elevated triglycerides. If you have metabolic syndrome, your low HDL is likely a downstream effect of the insulin resistance at its core.
Physical Inactivity and Diet
Regular physical activity is one of the strongest lifestyle predictors of HDL levels. Exercise increases the enzymes that help build and maintain HDL particles. Sedentary habits do the opposite, allowing those enzyme levels to fall and HDL production to slow.
Dietary patterns matter too, though the relationship is more nuanced than “eat more healthy fats.” Diets very low in all types of fat can lower HDL alongside LDL. Trans fats, still present in some processed foods, are particularly harmful because they raise LDL while simultaneously lowering HDL. Replacing refined carbohydrates with unsaturated fats from sources like olive oil, nuts, and fatty fish tends to support higher HDL levels.
Excess Body Weight
Carrying excess weight, particularly around the midsection, is closely tied to low HDL. Visceral fat (the fat surrounding your organs) is metabolically active and contributes to the same triglyceride-driven HDL breakdown described above. Weight loss, even a modest amount, reliably raises HDL. The effect is partly because losing fat reduces triglyceride levels, which slows HDL destruction, and partly because it improves insulin sensitivity.
Genetic Causes
Some people have persistently low HDL despite doing everything right with diet and exercise. Genetics often explain the gap. The most dramatic example is Tangier disease, a rare inherited condition caused by mutations in a gene called ABCA1. This gene controls a protein that releases cholesterol from cells so it can be loaded onto HDL particles. Without a functioning version of this protein, cholesterol gets trapped inside cells and HDL levels plummet, sometimes to nearly undetectable levels.
People who carry just one copy of the mutated gene (rather than two) don’t develop full Tangier disease but often have a milder condition called familial HDL deficiency, with HDL levels meaningfully below average. Other genetic variations affect the main structural protein of HDL itself. One well-studied mutation causes this protein to become unstable and get broken down in the blood before it can form functional HDL particles. Family members carrying this mutation have HDL levels roughly 20% lower and protein levels about 25% lower than their unaffected relatives.
Beyond these rare conditions, common genetic variants scattered across many genes each nudge HDL levels slightly up or down. If you’ve inherited an unfavorable combination, your baseline HDL may sit lower than average even with a healthy lifestyle.
Chronic Inflammation
Inflammation is one of the most underappreciated causes of low HDL. Autoimmune diseases like rheumatoid arthritis, lupus, psoriasis, inflammatory bowel disease, and ankylosing spondylitis all tend to push HDL down. In rheumatoid arthritis, the pattern is especially clear: the more severe the disease activity, the greater the drop in HDL. Levels of C-reactive protein (a marker of inflammation) track inversely with HDL, meaning higher inflammation correlates directly with lower HDL.
The mechanism appears to involve changes in how the liver and immune system handle lipid particles during an inflammatory state. Inflammatory signals alter the proteins and enzymes involved in HDL production and clearance, tipping the balance toward faster breakdown. This is why treating the underlying inflammation in these conditions often improves cholesterol numbers as a side benefit.
Acute Infections and Illness
If you’ve had blood work done during or shortly after an illness, your HDL reading may be misleadingly low. Bacterial, viral, and parasitic infections all cause HDL to drop, sometimes dramatically. In severe sepsis, HDL can fall below 10 mg/dL. The degree of HDL reduction during serious infections actually correlates with how sick someone is.
This drop is temporary and reflects the body’s acute inflammatory response rather than a lasting cardiovascular risk. It’s one reason a single low HDL reading during illness shouldn’t be taken at face value. Retesting once you’ve fully recovered gives a more accurate picture of your baseline.
Medications
Several commonly prescribed medications can lower HDL as a side effect. Beta-blockers (used for blood pressure and heart conditions) and certain older types of diuretics are known offenders. Anabolic steroids, including testosterone replacement at high doses, also reduce HDL. If your HDL dropped after starting a new medication, that connection is worth discussing with whoever prescribed it, since alternative drugs in the same class may have less impact on your lipid levels.
Why Low HDL Matters Less in Isolation
Low HDL rarely exists in a vacuum. It usually signals something else going on: insulin resistance, chronic inflammation, smoking, or excess weight. Treating the root cause typically brings HDL up as a byproduct. Interestingly, drugs designed to raise HDL artificially have consistently failed to reduce heart disease in clinical trials, which suggests that the HDL number on your lab report is more of a messenger than a direct player. The conditions driving it down are what actually increase your cardiovascular risk.
The good news is that the overall prevalence of low HDL in the U.S. has dropped significantly, from 22.2% in 2007-2008 to 14.2% as of 2023, likely reflecting improvements in smoking rates, awareness, and management of metabolic conditions.