Reducing elevated low-density lipoprotein (LDL) cholesterol is a key public health challenge. There is evidence that a number of foods and food components can significantly reduce LDL cholesterol. Food components, such as plant stanols and sterols, soya protein, beta-glucans and tree nuts may reduce LDL cholesterol by 3-9 %.
Sterols and stanols have a function in plants rather like that of cholesterol in humans. A high intake of these substances impairs uptake of cholesterol from the gut. They reduce total and LDL cholesterol and may beneficially influence other lipid variables such as apolipoprotein (apo) B/apo AI ratio and, in some studies, high-density lipoprotein (HDL) cholesterol and triglycerides (TGs).
Plant sterols/stanols may also affect inflammatory markers and coagulation parameters, as well as platelet and endothelial function.
Unfortunately, whilst the in vitro evidence for their beneficial effects on lipid profile is convincing, this does not translate with any compelling degree into prevention of primary cardiovascular events. Except in borderline normo/hypercholesterolaemia, prescription drugs (eg, statins) are more effective than stanol/sterol esters for lowering LDL cholesterol. The National Institute for Health and Care Excellence (NICE) does not recommend routinely advising patients to use them, until results of randomised controlled trials are known.
Sterols and stanols are ubiquitous in the plant world. They are most effective when taken with food and are produced commercially to add to food.They are usually sold in the form of margarine but can occur in other forms like yoghurt. Rich natural sources include rice bran, avocado oil, original wheatgerm and extra virgin olive oil.
There do not seem to be any significant clinical differences between plant sterols and stanols in terms of their effects on total cholesterol, LDL cholesterol, HDL cholesterol, or TG levels.
Effect on cholesterol
The evidence shows that there is considerable variation between individuals in response to stanols and sterols. They do tend to reduce LDL cholesterol and the effect is dose-related. In general terms, the reduction is between 10% and 20%. Daily consumption of 1-2 g of plant sterols or stanols has been shown to cause 10-20% reduction in LDL cholesterol.
Conclusions about sterols, stanols and cholesterol
There is circumstantial evidence supporting the relationship between ingestion of sterols and stanols and a reduction in cardiovascular risk and it would seem to suggest the following conclusions[7, 8]:
- Systematic reviews to date do seem to suggest a general trend that shows that stanols and sterols reduce LDL cholesterol in people with normal and moderately raised cholesterol and that this effect is related to dose. They are also effective in reducing LDL cholesterol in more severe cases, as in familial hypercholesterolaemia, including homozygous individuals.
- The advent of powerful statins has led to neglect of dietary manipulation but sterols can be used in addition to statins to gain maximal effect.
- Plant sterol/stanol supplements, as part of a healthy diet, may represent an effective means of delivering LDL cholesterol lowering similar to plant sterols/stanols delivered in various food formats[4, 11].
- It is not yet clear as to the optimum intake of sterols/stanols. Foods enriched with 2 g of phytosterols/stanols per day have been shown to have a significant cholesterol-lowering effect.
- One study suggests that plant sterols work best when taken 'little and often' rather than in one large daily dose.
Other benefits of sterols
Sterols have been shown to have a beneficial effect in terms of prevention of cancer, especially colorectal cancer, breast cancer and prostate cancer. Not all studies have reported positive results and a number are based on samples of animals given carcinogens. Sterols appear to have antioxidant properties that would account for benefit with regard to both cancer and atheroma.
Although sterols are natural products ubiquitous in food, their safety cannot be assumed.
- The ability to lower cholesterol is similar both in men and women; however, women seem to be much more susceptible to stanols causing impairment of the absorption of fat-soluble vitamins.
- Sterols are not recommended for pregnant or lactating women or for children aged under 5. This is because they have been shown to reduce the level of carotenoids, including vitamin A which is closely associated with fetal development. Moreover, the developing brain needs cholesterol.
- Sitosterolemia is a rare autosomal recessive inherited disorder which is known to be associated with high maternal absorption of plant sterol and cholesterol. It results in coronary heart disease at an early age.
Recommendations for patients
NICE recommends that patients should not routinely be advised to take plant sterols and stanols for the primary prevention of cardiovascular disease. This is based on the grounds that there are as yet no randomised controlled trials examining the effect of these substances on primary and secondary prevention with respect to cardiovascular outcomes. This recommendation may be subject to revision once the necessary data become available.
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