HDL Cholesterol

HDL, high-density lipoprotein, is the particle that carries cholesterol the other way. Where LDL brings cholesterol from the liver to the tissues, HDL collects surplus cholesterol from the tissues and from the artery wall and brings it back to the liver, which disposes of it through bile. That reverse transport earned HDL its nickname as the good cholesterol. Your HDL cholesterol is the amount of cholesterol on its way out like that. The nickname is a simplification. People with a higher HDL get cardiovascular disease less often, but raising HDL artificially with drugs turned out not to lower the risk in large trials. So the number mostly says something about the metabolism it comes from. HDL rises when you exercise and do not smoke, and falls with belly fat and insulin resistance; a low HDL says something is off in that pattern, more than that HDL itself is the culprit. Your report shows HDL as one number in millimoles per litre (mmol/L). Because a high HDL is no cause for concern, your lab sometimes prints only a lower limit and sometimes a range with a lower and an upper bound. The table further down shows what each lab uses.

HDL is the blood fat value that shows most honestly whether your lifestyle is working, because you can hardly get around it: no supplement or diet week lifts it, only exercise, a slimmer waist and not smoking. So a low HDL rarely comes alone. It almost always belongs to a pattern: raised triglycerides, belly fat, insulin resistance, little exercise and smoking. In that pattern the LDL particles are also smaller and denser, and those enter the artery wall more easily. A low HDL is therefore an early signal of a metabolism moving the wrong way, often years before your blood sugar or your LDL shows anything. Below 1.0 mmol/L in men and 1.2 mmol/L in women it counts as a marker of increased risk. For estimating your risk, HDL does not enter on its own but through non-HDL cholesterol: your total cholesterol minus your HDL, the cholesterol in all the particles that build up in the artery wall. That way a low HDL counts, without a high HDL being able to mask a high LDL.

A low HDL almost always points to lifestyle: little exercise, belly fat, smoking, and the insulin resistance that goes with them. Plenty of sugar and fast carbohydrates depress HDL too, through higher triglycerides. Occasionally a very low HDL is inherited, roughly below 0.60 mmol/L without strongly raised triglycerides: an inborn disorder of HDL metabolism. A high HDL is partly inheritance and partly lifestyle, and there is no upper limit above which it is harmful. What does hold: a high HDL does not make up for a high LDL. So always read HDL beside LDL, triglycerides and non-HDL. A low HDL with high triglycerides is the metabolic pattern that deserves attention; a high HDL with a low LDL is the most favourable picture. HDL listens to what you do, only more slowly than triglycerides. Exercise is the strongest lever: endurance training, cycling, brisk walking, preferably every day. Losing weight around the middle and stopping smoking follow; after stopping, HDL recovers noticeably. Replace saturated fat with unsaturated fat from olive oil, nuts and oily fish, and keep sugar limited: whatever brings your triglycerides down brings HDL up. Count on months, not weeks, and look at the pattern. If your triglycerides fall with it and your waist shrinks, you are doing the right thing, even when the HDL number follows only slowly. In the table further down you will see that some labs print an upper limit and others do not. That upper limit is the top of what that lab measures across the population, not a limit above which something is wrong.