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HDL-C (High-density lipoprotein cholesterol) |
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The following is an extract from “Stop that Heart Attack!” 3rd edition, by Dr Derrick Cutting. (Class Health).
Checking your cholesterol
You could check your cholesterol level with a fingerprick test at your doctor’s surgery, on the high street or even at home with a d.i.y. test kit. The accuracy of these tests is variable and it would be unwise to base the whole direction of your life on a single reading of this kind. You can be more confident about accuracy if your doctor arranges for a blood sample to be taken from a vein and analysed in a hospital laboratory.
Samples taken when you haven’t fasted are suitable for measuring total cholesterol (but not for telling you how much of it is HDL or LDL-cholesterol). The total cholesterol is not significantly altered by a 12 hour fast and a non-fasting or ‘random’ level is useful as a screening test to pick out people at high risk.
Triglycerides are quite different. The level of these fats in the blood shoots up and down according to what you’ve been eating in the last few hours. So measurement of triglycerides is pointless unless you’ve been fasting for 12 hours. This is one of the easiest fasts you could do. You can finish a banquet at 9 o’clock in the evening, have blood taken at 9 o’clock the following morning and tuck into breakfast immediately afterwards. You can drink water during the fast, but avoid other drinks.
Measurement of triglycerides and HDL-cholesterol on a fasting blood sample allows the LDL-cholesterol to be calculated (in mmol/l) with this formula:
LDL-chol+(total chol - HDI0chol) - triglycerides/2.19
This formula is not accurate if the triglyceride concentration is above 4.5 mmol/l.
So, if your doctor arranges a fasting lipid profile, it will usually tell you your blood levels of the following:
• Total cholesterol
• HDL – cholesterol
• LDL – cholesterol
• Triglycerides
Some laboratories do not measure the HDL-cholesterol unless the total cholesterol is above 6.5 mmol/l. This policy may be acceptable for general screening but there are circumstances in which the doctor will want to know the HDL-cholesterol level, even if the total is not raised. For example, the doctor may specifically ask the laboratory to measure the HDL-cholesterol if:
• You have a significant family history (e.g. brother died of a heart attack aged 45);
• You are taking certain beta-blockers (such as propranolol) that could reduce the HDL-cholesterol and raise triglycerides;
• You are already on a strict diet or taking a drug to lower cholesterol.
There are times when measuring cholesterol-levels can be misleading; for example, it is advisable to wait three months after pregnancy, surgery or serious illness including a heart attack, before having a cholesterol test. (Levels measured just after a heart attack, within 24 hours, are usually considered reliable). Similarly, you should not have your cholesterol checked within three weeks of having flu or a similar illness because the result may be artificially low (unless this is for an insurance medical in which case perhaps it is the ideal time to have the test).
Maintaining the high
If you have changed your diet radically, you may be quite elated on re-testing to find your cholesterol has come crashing down. Well done, but spare a thought for your HDL-cholesterol. What’s happened to that? Remember, your aim is:
To keep the HIGH-Density Lipoprotein (HDL) up HIGH.
It may be that your doctor is unable to tell you your HDL-cholesterol level because, now that your total cholesterol is below 6.5 mmol/l, the laboratory hasn’t measured it. This really is unsatisfactory and, if you have made a drastic change to your diet (just as if you had taken a drug to lower your cholesterol), you need to check your HDL. Most laboratories will measure it if the doctor specifically requests it.
It is likely that, if you have switched to a very low-fat diet with a very high carbohydrate intake, your HDL-cholesterol will have dropped a little. (There may also be some rise in the triglyceride level but this usually falls again after several months on this sort of diet). In addition, you may remember that polyunsaturated fatty acids are helpful in lowering total cholesterol but, unfortunately, tend to push down the HDL-cholesterol too.
Aim to keep your HDL-cholesterol at 1 mmol/l or above. If it has dropped to, say 0.8 mmol/l because of your low-fat, high carbohydrate diet (and you’ve got everything else in your diet and lifestyle right) and you’ve brought your LDL-cholesterol down as well (to, say, 3.0 mmol/l) then you probably don’t have much to worry about. People in some parts of the world have low levels of HDL-cholesterol because most of their energy comes from carbohydrate; they have very low saturated fat intakes, low levels of LDL-cholesterol and low rates of heart disease. Indeed, as a group, vegetarians in westernised societies have lower HDL-cholesterol levels than meat eaters – and lower rates of heart disease.
Here are some tips worth trying if your HDL-cholesterol is struggling to get above 1 mmol/l:
• Add some good sources of mono-unsaturated fatty acids to your diet, such as olive oil, rapeseed oil, olives, avocados, hazelnuts and almonds.
• Cut down any unnecessary sources of polyunsaturates, e.g. sunflower, safflower, soya or corn oils; sunflower spread or sunflower seeds.
• Eat a low-GI diet. Cut down on foods with a high glycaemic index such as baguettes, white bread and instant rice. Eat more foods with a low GI, such as pasta and pulses. Spaghetti tossed in a little olive oil (delicious with garlic) would be a better choice than baked potato with sunflower spread.
• If you smoke, you must stop. Apart from all
the other harmful effects, smoking depresses HDL-cholesterol.
• Take more exercise. Aerobic exercise raises HDL-cholesterol levels. 20 minutes three times a week is better than nothing, but you may need a lot more than this to make a significant impact on your HDL concentration.
• A little alcohol (e.g. one or two units a day) can help to lift drooping HDL-levels.
• If you are a post-menopausal woman and not taking hormone-replacement therapy, oestrogen can help to lift HDL- and lower LDL-cholesterol.
• If you are taking a non-selective beta-blocker (such as propranolol), it may be reducing your HDL-cholesterol and raising your triglycerides. This would be something to discuss with your doctor.
We noted that someone who has a very low-fat, high-carbohydrate diet and a healthy lifestyle need not be too concerned about a rather low HDL-cholesterol level. If you are an overweight, inactive smoker with a low HDL-cholesterol, that’s quite different. Urgent action is needed.
If your HDL-cholesterol is below 0.6 mmol/l and, especially if you have a family history of heart disease, you should have specific medical advice about this.
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