Cholesterol and blood fats: what the numbers mean

The NHS defines high cholesterol as having too much of a fatty substance called cholesterol in the blood. The body does need some of it, so the aim is balance rather than zero. Too much can block blood vessels and make heart problems or a stroke more likely.

Triglycerides are a different fat. The American Heart Association (AHA) calls them the most common type of fat in the body, and says they store excess energy from the diet. Cholesterol travels through the blood inside particles called lipoproteins. Doctors often use the term "blood fats" (lipids) to cover cholesterol and triglycerides together.

Two kinds of lipoprotein matter most. The AHA describes low-density lipoprotein (LDL) as the "bad" cholesterol and high-density lipoprotein (HDL) as the "good" one, because a healthy HDL level may help protect against heart attack and stroke.

HDL carries LDL away from the arteries and back to the liver, where the LDL is broken down and passed from the body. The AHA adds a caution: HDL does not eliminate LDL cholesterol, and only a fraction of blood cholesterol is carried by HDL. The labels "good" and "bad" are a simplification, though a helpful one.

The AHA says LDL cholesterol contributes to fatty build-ups in the arteries, known as atherosclerosis. This narrows the arteries and increases the risk of heart attack, stroke and peripheral artery disease (narrowed arteries elsewhere in the body, such as the legs). The AHA also notes that a high triglyceride level combined with high LDL or low HDL is linked with fatty build-ups within artery walls.

This build-up usually happens quietly. The NHS states that high cholesterol does not usually cause symptoms, and that you can only find out you have it from a blood test. For what a blocked artery can feel like when it does cause trouble, see heart attack signs and what to do and stroke signs and what to do. For the basics of the organ itself, how the heart works is a good companion.

Measurement is a blood test, often called a lipid panel or lipid profile. NHLBI says it measures LDL cholesterol, HDL cholesterol and triglycerides, and reports total cholesterol as well. A provider may ask for fasting for 8 to 12 hours beforehand, though NHLBI also lists non-fasting samples, so instructions vary.

Numbers and units differ between services. As examples only, the NHS gives general figures in millimoles per litre (mmol/L): total cholesterol below 5, and non-HDL cholesterol below 4. NHLBI gives its general goal in milligrams per decilitre (mg/dL): non-HDL below 130. These are not personal targets and the two sets cannot be compared directly without converting units.

Both services stress that the right level depends on the person. The NHS says a good target depends on things like age and health conditions, and that a doctor weighs overall heart disease risk. NHLBI advises checking with your provider on the lipid levels that are best for you. Readers should treat any figure on a web page, including these, as background rather than a goal.

The NHS lists eating fatty food, not exercising enough, being overweight, smoking and drinking alcohol among the causes. It also says high cholesterol can run in families and is more likely in people over 50, in men, after the menopause, and in people of South Asian or sub-Saharan African origin.

The same NHS pages describe lifestyle steps: cutting down on saturated fat, eating more oily fish, wholegrains, nuts, fruit and vegetables, being active, and not smoking. On activity, the NHS suggests at least 150 minutes of moderate-intensity exercise a week; physical activity and the heart covers this in more detail. Salt is a separate issue, but it often features in the same conversations about heart risk, so see salt and heart health. Raised cholesterol also often sits alongside high blood pressure.

Medicines and inherited cholesterol

Some people need medicine as well. NHLBI calls statins the most common medicine used to treat high blood cholesterol, and says a provider may discuss them alongside cholesterol levels, heart disease risk, other conditions and lifestyle. Whether to take any medicine is a decision for a clinician and the person concerned.

A small number of people have inherited high cholesterol that starts at a young age, known as familial hypercholesterolaemia. The NHS points readers to HEART UK for information about it. The NHS also lists family history as a factor in ordinary high cholesterol.

Because raised cholesterol rarely gives warning signs, a blood test is the only way to know where you stand, and a clinician can explain what your results mean for you. Testing is something to raise with a clinician, particularly with a family history of high cholesterol or other risk factors. Chest pain that is crushing or spreading to the arm, neck or jaw, or sudden signs of stroke, need emergency help at once. Emergency numbers differ by country, so use your local emergency number.

Cholesterol is needed by the body, but a high level of LDL can feed the plaque that narrows arteries. A lipid blood test shows LDL, HDL and triglycerides, and the target that suits you depends on your age, health and overall risk, and on which country's guidance is used. Food, activity, weight, smoking and alcohol all play a part, and medicines such as statins are one option a clinician may discuss.