What Does Cholesterol Do in the Body?
Cholesterol has a reputation as something to eliminate, which gets the biology backwards. Your body makes cholesterol on purpose because it cannot function without it. The problem is not its existence but how much of it is circulating and in what form.
What cholesterol actually does
Cholesterol is a waxy lipid found in every cell you have. It does three jobs that nothing else does as well.
It builds cell membranes
Every cell is wrapped in a membrane, and cholesterol sits inside that membrane controlling how rigid or fluid it is. Too little and membranes become unstable. This is structural work, happening in all of your cells, all the time.
It is the raw material for hormones
Cortisol, aldosterone, testosterone, oestrogen and progesterone are all built from cholesterol. Without it, the body cannot manufacture any of them.
It makes vitamin D and bile acids
When sunlight hits your skin, it converts a cholesterol derivative into vitamin D. Cholesterol is also used in the liver to produce bile acids, which let you absorb fats and fat soluble vitamins from food. More on the vitamin side in our guide to good sources of vitamin D.
Where cholesterol comes from
Roughly 75 to 80 per cent of the cholesterol in your blood is made by your own liver. Only the remainder comes from food.
This is why advice about dietary cholesterol changed. For most people, eating cholesterol has a smaller effect on blood cholesterol than once assumed, because the liver compensates by making less. Saturated fat and trans fat influence blood levels more than dietary cholesterol does.
HDL and LDL are not cholesterol
This is the detail that makes the rest make sense.
Cholesterol does not dissolve in blood, so it cannot travel on its own. It is packaged inside particles called lipoproteins. HDL and LDL are those delivery vehicles, not two different kinds of cholesterol.
| Particle | Stands for | What it does |
|---|---|---|
| LDL | Low density lipoprotein | Carries cholesterol from the liver out to the tissues |
| HDL | High density lipoprotein | Collects excess cholesterol and returns it to the liver |
| Triglycerides | Not a lipoprotein | A separate blood fat used for energy storage |
LDL is called “bad” because when there is too much of it circulating, the particles can lodge in artery walls and contribute to plaque. HDL is called “good” because it moves cholesterol in the other direction. Both are necessary.
Reading a lipid panel
A standard lipid panel reports four figures, usually in mg/dL.
- Total cholesterol. The least useful on its own, because it adds together particles that behave differently.
- LDL cholesterol. The number most treatment decisions are based on.
- HDL cholesterol. Higher is generally better.
- Triglycerides. Strongly affected by alcohol, refined carbohydrate and recent meals.
Targets are not universal. Someone who has already had a heart attack is given a much lower LDL target than someone with no risk factors. This is why a result described simply as “high” means little without context.
What changes the numbers
Things that tend to lower LDL:
- Replacing saturated fat with unsaturated fat, for example olive oil or nuts instead of butter
- Soluble fibre from oats, beans, lentils and fruit
- Losing excess weight
- Regular aerobic exercise
- Stopping smoking, which also raises HDL
Things that tend to raise triglycerides:
- Alcohol
- Sugar and refined carbohydrate
- Excess calories generally
Genetics set a large part of where your numbers sit. Familial hypercholesterolaemia is an inherited condition that produces very high LDL from a young age regardless of diet, and it needs medical treatment rather than lifestyle adjustment alone.
Frequently asked questions
Can cholesterol be too low?
Very low levels are uncommon and are usually a sign of another problem such as liver disease, malnutrition or an overactive thyroid, rather than something people achieve by healthy eating.
Do eggs raise cholesterol?
Eggs are high in dietary cholesterol but low in saturated fat. For most people they have a modest effect on blood cholesterol. People with diabetes or existing heart disease are sometimes advised to moderate intake.
How often should cholesterol be checked?
Adults without risk factors are commonly tested every four to six years, more often with risk factors, a family history or existing treatment. Your doctor sets the interval.
Do I need to fast before a cholesterol test?
Not always. Non fasting panels are accepted for routine screening in many places. Fasting is more often requested when triglycerides are the focus.
Does high cholesterol cause symptoms?
No. Like high blood pressure, it is found through testing rather than through how you feel.
Is HDL always good?
Higher HDL is generally associated with lower risk, but very high HDL has not been shown to add further protection, and raising HDL with drugs has not reduced heart attacks in trials. It is better treated as a marker than a target.
This article is general information, not medical advice. Discuss your own results and targets with a doctor.
