IngredientsThe term alpha phytosterol refers to the α-isomeric form of phytosterols — plant-derived sterol compounds most closely associated with α-sitosterol (alpha-sitosterol), one of several isomers in the sitosterol family. Phytosterols and phytostanols include various isomers such as the α and β isomers — for example, α-sitosterol and β-sitostanol, which comprise one of the most effective phytosterols and phytostanols for lowering serum cholesterol in mammals. In common usage, "alpha phytosterol" is employed as a general ingredient name encompassing the sterol family as a whole, with α-sitosterol being its most specific chemical referent. The broader phytosterol class is formally defined by its biochemistry: phytosterols are chemically classified as triterpenes, a class of terpenes composed of six isoprene units; these natural products include more than 200 different phytosterols and more than 400 other triterpenes.
Phytosterols are phytosteroids, similar to cholesterol, that serve as structural components of biological membranes of plants. They encompass plant sterols and stanols, and more than 250 sterols and related compounds have been identified. Structurally, phytosterols are similar to cholesterol; however, cholesterol has a side-chain composed of 8 carbon atoms, whereas most phytosterols contain 28 or 29 carbon atoms, with a side-chain composed of 9 or 10 carbon atoms and one or two carbon-carbon double bonds. Typically, a 5,6-double bond appears at the steroid nucleus, and sometimes the alkyl side chain may also contain a double bond. More specifically, phytosterols differ from cholesterol in the side chain bound at their C-17 position; sitosterol, as an example, has an ethyl group linked at C-24 of the side chain, while campesterol has a methyl group in the same position, which is empty in cholesterol.
These compounds can be classified as sterols or stanols, according to the presence or absence of a double bond at the Δ5-position. Non-limiting examples of phytosterols include 4-desmethylsterols (e.g., β-sitosterol, campesterol, stigmasterol, brassicasterol, 22-dehydrobrassicasterol, and Δ5-avenasterol), 4-monomethyl sterols, and 4,4-dimethyl sterols (triterpene alcohols) (e.g., cycloartenol, 24-methylenecycloartanol, and cyclobranol).
Phytosterols, encompassing plant sterols and stanols, are natural steroids that are widely found in different parts of plants (including roots, stems, leaves, flowers, fruits, and whole grasses) and are an important part of plant cell membranes. Phytosterols occur in many food plants, nuts, seeds, vegetables, and edible oils.
While more than 250 phytosterols from different plant classes have been identified to date, β-sitosterol, campesterol, and stigmasterol are the most abundant. The main source of phytosterols in large-scale production is the by-products from the process of refining oils. β-Sitosterol is found in cereals, vegetables, and fruits in concentrations of 0.24–0.61, 0.02–0.41, and 0.02–0.34 g kg⁻¹, respectively. Vegetable oils are rich sources of β-sitosterol containing 0.24–8.79 g kg⁻¹ (representing 33%–91% of total phytosterols); specifically, olive oil and olive pomace oil have a high β-sitosterol concentration ranging between 0.91 and 1.52 g kg⁻¹ (representing 75%–90% of total phytosterols).
The most abundant phytosterol in most edible oils is β-sitosterol, which is highest in corn oil at 4.35 ± 0.03 mg/g, followed by campesterol in canola oil at 1.84 ± 0.01 mg/g. At least 44 naturally-occurring phytosterols have been discovered, and generally are derived from plants, such as corn, soy, wheat, and wood oils; however, they also may be produced synthetically to form compositions identical to those in nature or having properties similar to those of naturally-occurring phytosterols. Industrial-scale extraction draws upon a variety of sources: phytosterols may be obtained from the processing of plant oils (including aquatic plants) such as corn oil and other vegetable oils, wheat germ oil, soy extract, rice extract, rice bran, rapeseed oil, sesame oil, and fish oil. Alternatively, phytosterols may be obtained from tall oil pitch or soap, by-products of forestry practice.
Free phytosterols extracted from oils are insoluble in water, relatively insoluble in oil, and soluble in alcohols. The sterols are abundant in nature; they exist in both esterified and free alcohol forms. To overcome their poor solubility and enhance incorporation into food products, phytosterols are commonly esterified with fatty acids. By condensing the hydroxyl group of these phytosterols with the carboxyl group of a fatty acid to form an ester, enhanced absorption of the resultant phytosterol esters can be achieved.
Authorised phytosterols as a novel food concern phytosterols extracted from plants, which may be presented as free sterols and stanols or esterified with food-grade fatty acids. Non-limiting examples of suitable phytosterol and phytostanol esters include sitosterol acetate, sitosterol oleate, and stigmasterol oleate, as well as their corresponding phytostanol esters. Commercially, phytosterols (including the alpha-isomer fraction) appear in multiple delivery formats: fortified margarines, yoghurts, and dairy drinks; as well as dietary supplement capsules, softgels, and tablets. A newer formulation of plant stanols is in dry stanol lecithin complexes. One US-developed product can be given as 4 tablets before breakfast and supper for a daily dose of 1.8 g; tablets containing 225 mg of stanols in dried stanol/lecithin complexes were designed to disintegrate in less than 10 minutes to deliver stanols into the digestion process.
Phytosterols, including the alpha-sitosterol fraction, were not historically isolated or consumed as discrete compounds. Their traditional significance is inseparable from the plant foods in which they naturally occur. The use of phytosterol-rich nutritional products has a historical basis rooted in traditional diets rich in fruits, vegetables, nuts, and seeds.
One of the most thoroughly documented historical dietary patterns rich in phytosterols is the Mediterranean diet. The Mediterranean diet originates in the food cultures of ancient civilizations which developed around the Mediterranean Basin and is based on the regular consumption of olive oil (as the main source of added fat), plant foods (cereals, fruits, vegetables, legumes, tree nuts, and seeds), the moderate consumption of fish, seafood, and dairy, and low-to-moderate alcohol intake. Originating in ancient civilizations such as the Minoans (7000–2000 BC), Phoenicians (1200–332 BC), Classical Greeks (479–323 BC), and Romans (31 BC–476 AD), the Mediterranean Diet developed as a plant-based diet supplemented with olive oil, fish, and moderate amounts of meat and wine. Phytosterols comprised in nuts, whole grains, seeds, vegetables, and fruits also contribute to the control of the intestinal absorption of cholesterol.
Herbal blends featuring phytosterol-rich botanicals such as saw palmetto, pumpkin seed, and nettle root have been revered in both Western and Eastern traditions for supporting prostate health, urinary function, and cardiovascular well-being. In European ethnomedicinal tradition, plant extracts from saw palmetto (Serenoa repens) and pumpkin seed (Cucurbita pepo) — two of the richest known botanical sources of β-sitosterol and related alpha phytosterol fractions — were employed for urinary complaints associated with prostate enlargement. Phytosterol derived from plants has long been used for the medical treatment of benign prostatic hyperplasia (BPH) in Europe but not in Japan.
The pharmacological recognition of the cholesterol-lowering action of phytosterols has a mid-20th-century origin. The hypocholesterolaemiant action of phytosterols has been known since the 1950s. Phytosterols have a long history of safe use in humans; the drug Cytellin® was marketed in the United States between 1954 and 1982. This early pharmaceutical application represented the first formal clinical use of sitosterol as a cholesterol-lowering agent, predating the modern era of statin therapy.
While "alpha phytosterol" as a commercial ingredient encompasses the alpha-isomeric fractions, the phytosterol family's principal bioactive constituents and the most studied include:
The best-characterised mechanism of phytosterols is competitive inhibition of intestinal cholesterol absorption. In the intestinal lumen, dietary fat, cholesterol, and bile acids mix to form micelles. Phytosterols compete with cholesterol to enter these micelles. Phytosterols displace cholesterol from intestinal micelles, reducing the pool of absorbable cholesterol, but they are also rapidly taken up by enterocytes and increase expression of the adenosine triphosphate-binding cassette A1 sterol transporter.
Phytosterols not only reduce the uptake of cholesterol in the intestinal lumen and affect its transport, but also regulate the metabolism of cholesterol in the liver. In addition, phytosterols can significantly reduce the plasma concentration of total cholesterol, triglycerides, and low-density lipoprotein cholesterol (LDL-C), with a dose-response relationship. Phytosterols can also activate the liver X receptor α-CPY7A1 mediated bile acids excretion pathway and accelerate the transformation and metabolism of cholesterol.
Although the bioavailability of phytosterols is only 0.5–2%, they can still promote cholesterol balance in the body. This relatively low systemic bioavailability means that their primary effects are exerted locally in the gastrointestinal tract.
Evidence is now emerging that phytosterols exert beneficial effects on non-lipid variables such as inflammatory and oxidative stress markers, coagulation parameters, and endothelial function. In the context of prostate inflammation, animal studies indicate that phytosterols could obviously reduce serum IL-1β, TNF-α, prostate COX-2, and 5-LOX expression and improve IL-2 levels. These results demonstrated that phytosterols had good therapeutic effects on chronic abacterial prostatitis; participation of immune regulation and inhibiting COX-2 and 5-LOX expression may be the mechanisms of action.
As a natural free-radical scavenger, the peroxyl radical scavenging activity of β-sitosterol is primarily via hydrogen transfer (HT) reaction when there is medium reactivity (such as ·OOH and ·OOCH₃). When the peroxyl radicals are significantly reactive, it can be explained by the radical adduct formation (RAF) mechanism. Furthermore, phytosterols could not only increase the activity of antioxidant enzymes (SOD, CAT, GPx, etc.) but also reduce the level of peroxides (ROS, MDA, etc.) to alleviate oxidative stress.
Several possible anticancer mechanisms of phytosterols have been proposed, such as inhibiting the production of carcinogens; inhibiting the proliferation, invasion, and metastasis of cancer cells; inducing apoptosis; and arresting the cell cycle. Phytosterols regulate important signal transduction processes such as NF-κB, PI3K/Akt, and MAPK/ERK that drive cell growth, survival, and metastasis. The mechanism of the tumour growth inhibitory effect of β-sitosterol may be related to protein kinase C (PKC) and the sphingomyelin cycle pathway.
Beta-sitosterol has also been shown to inhibit the 5α-reductase enzyme, thereby behaving similarly to finasteride and dutasteride, which are widely used to treat prostatic enlargement. Additionally, anti-androgenic, anti-inflammatory, antioxidant, and pro-apoptotic mechanisms of phytosterols have been proposed in the context of benign prostatic hyperplasia.
Experimental studies have shown that oral administration of β-sitosterol in hyperglycaemic rats decreased their glucose and insulin levels. The proposed pathophysiological mechanism involves the mediation of the uptake of glucose by the adenine monophosphate-activated protein kinase (AMPK).
Evidence strength: Strong for LDL-C lowering; no definitive evidence for hard cardiovascular endpoints.
The clinical evidence for plant sterols and stanol esters is very strong. Over a hundred randomised placebo-controlled trials have consistently shown a significant drop in total and LDL cholesterol following a daily intake of plant sterols or stanol esters over a period of at least two weeks. The wealth of evidence has led to both a US FDA- and EFSA-approved health claim for foods fortified with plant sterols or stanol esters.
Since the late 1950s, numerous studies have consistently indicated that foods enriched with phytosterols reduce the concentrations of LDL-cholesterol. The dose is typically around 2–4 g/day and the reduction in LDL-cholesterol is approximately 10%. Ingestion of 3 g of phytosterols per day can reach the plateau period, and this dose can reduce LDL-C by about 10.7%.
A placebo-controlled, double-blind crossover trial investigated a phytosterol emulsion for dietary supplements. The primary objective was to determine the impact of 1.5 g/day phytosterol equivalents on LDL-C concentrations; thirty-two healthy adults were randomly assigned to receive placebo or treatment followed by a washout period, each phase lasting one month.
A controlled feeding trial by Racette and colleagues at Washington University assessed dose effects: results indicated that phytosterols consumed in moderate and high doses substantially enhanced fecal cholesterol excretion and reduced percentage intestinal cholesterol absorption relative to a phytosterol-deficient diet, and the effect was dose-dependent.
Regarding guideline recommendations: the ESC/EAS joint guidelines recommend 2 g phytosterol supplementation in individuals with high cholesterol levels at intermediate and low cardiovascular risk; in those who do not qualify for pharmacotherapy, in high- and very-high-risk patients on top of pharmacotherapy who fail to achieve LDL-C goals or who cannot be treated with statins, and in individuals with familial hypercholesterolaemia. The American Heart Association, on the other hand, restricts the use of phytosterols to patients with familial hypercholesterolaemia and for secondary prevention and emphasises that more information is required to recommend plant sterols in the general population.
Despite clear LDL-C lowering, the evidence for preventing actual cardiovascular events remains absent. No data deriving from formal randomised clinical trials are available to translate this well-described effect of phytosterols on plasma LDL-cholesterol levels into measurable direct clinical effects on cardiovascular morbidity and mortality. To date, there are no randomised placebo-controlled trials to investigate the impact of phytosterol supplementation on hard cardiovascular outcomes. Cardiovascular outcome trials investigating foods fortified with plant sterols/stanols in individuals at low or moderate CVD risk are not feasible, given the sample size (n > 50,000) required for adequate statistical power.
Evidence strength: Moderate (positive but short-term RCT data; long-term outcomes unknown).
The Cochrane systematic review by Wilt et al. remains the foundational source. Five hundred nineteen men from four randomised, placebo-controlled, double-blind trials (lasting 4 to 26 weeks) were assessed. β-Sitosterols improved urinary symptom scores and flow measures. The weighted mean difference (WMD) for the IPSS was -4.9 IPSS points (95% CI = -6.3 to -3.5, n = 2 studies). The WMD for peak urine flow was 3.91 mL/s (95% CI = 0.91 to 6.90, n = 4 studies) and the WMD for residual volume was -28.62 mL (95% CI = -41.42 to -15.83, n = 4 studies). β-sitosterols did not significantly reduce prostate size compared to placebo; withdrawal rates for men assigned to β-sitosterol and placebo were 7.8% and 8.0%, respectively.
A landmark randomised, double-blind, placebo-controlled multicentre study comprised 200 patients with symptomatic BPH treated with either 20 mg of beta-sitosterol 3 times per day or placebo for 6 months. This study found significant improvement in symptoms and urinary flow parameters that demonstrated efficacy of beta-sitosterol in the treatment of BPH.
A smaller Japanese study evaluated phytosterol at a different dosage: phytosterol containing 180 mg of sitosterol per day was given to 12 patients with BPH in two or three divided doses for three months. The symptoms were assessed monthly using the International Prostate Symptom Score (IPSS) and quality-of-life (QOL) score. The IPSS and QOL scores showed significant improvement (p < 0.05), while the peak flow rate and residual urine volume showed slight but not significant improvement.
Multiple studies show that beta-sitosterol significantly improves lower urinary tract symptoms (LUTS) associated with BPH, but to an extent that is generally less effective than that achieved by pharmaceutical-grade alpha-adrenergic receptor antagonists or 5α-reductase inhibitors. The Cochrane review's overall conclusion was that the evidence suggests non-glucosidic β-sitosterols improve urinary symptoms and flow measures, but their long-term effectiveness, safety, and ability to prevent BPH complications are not known. A more recent review affirmed that phytosterols might be a useful pharmacological treatment option for men with mild to moderate BPH, but the lack of standardised extracts linked with the regulation of dietary supplements containing phytosterols and experimental evidence to elucidate the mechanisms of action limit the use of phytosterols in BPH.
Evidence strength: Preliminary/mixed in humans; better established in preclinical models.
The anti-inflammatory effects induced by plant sterols/stanols have been demonstrated in in vitro studies and in experimental animal models. However, not all the beneficial effects seen at an experimental level have translated into clinical benefit. Clinical studies that evaluate the association between phytosterol consumption and inflammatory variables (CRP and cytokines) are inconsistent and have not yet provided a solid answer.
Evidence strength: Preclinical and epidemiological only; insufficient human clinical trial evidence.
Phytosterols have multifactorial modes of action such as antioxidant, anti-inflammatory, and apoptotic, which render them potentially useful in the prevention and treatment of prostate, breast, colon, bladder, and skin cancer. Phytosterols induce apoptosis, block the cell cycle, and abrogate the invasion and metastasis of cancer cells, offering a multi-manifestation treatment of cancer. Nevertheless, their clinical use is limited due to factors such as low bioavailability, which may be overcome with research in nanotechnology and drug delivery schemes. Based on preclinical and epidemiological studies, phytosterols may be used as a useful adjunctive component to cancer treatments. More studies are required to work out clinical testing and streamlined delivery to maximise their effectiveness in cancer treatment.
Evidence strength: Preliminary; limited human data, mostly from animal models.
Over the last decade, emerging evidence supports the theory that supplementation with phytosterols and phytostanols has a hypoglycaemic effect. However, randomised trials in humans have confirmed a beneficial, but not clinically significant, effect. The research base in this area is considered early-stage and requires larger, well-powered human trials.
Evidence strength: Weak to preliminary.
Endothelial function, evaluated as flow-mediated dilation, would also improve after a treatment with phytosterols, but this is also controversial. Mechanistically, this effect could explain the mild reduction in blood pressure found in a recent meta-analysis.
People ingest 100–400 mg/d phytosterols, mainly from vegetable oils, bread, cereals, nuts, and vegetables. The daily phytosterol ester concentrations are 300 mg/day for a general diet in the population, about 500 mg/day in Mediterranean countries, and about 600 mg/day in vegetarians.
For cholesterol-lowering purposes in supplementation or fortified foods:
For BPH / prostate health (as reported in clinical trials):
There are still no available studies with long-term follow-up ensuring the safety of regular consumption of products enriched with phytosterols, as highlighted in recent publications of the European Society of Cardiology / European Atherosclerosis Society and the American Heart Association / American College of Cardiology. However, based on the absence of adverse effects in short-term studies and experimental studies, several authors consider that the consumption of phytosterols is safe.
Phytosterolemia (sitosterolemia) is a rare autosomal recessive sterol storage disease caused by mutations in either of the ATP binding cassette transporter genes (ABCG5 or ABCG8), leading to impaired elimination of plant sterols and stanols, with their increased accumulation in the blood and tissues. The disease is characterised by substantially elevated serum plant sterols and stanols, with moderate to high plasma cholesterol levels, and increased risk of premature atherosclerosis. Haematological abnormalities including macrothrombocytopenia, stomatocytosis, and haemolysis are frequently observed in sitosterolemia patients. People with sitosterolemia should avoid foods or supplements with added plant sterols.
Although phytosterols decrease LDL-cholesterol levels, there is no evidence that they reduce the risk of cardiovascular diseases; on the contrary, some studies suggest an increased risk of atherosclerosis with increasing serum levels of phytosterols. A genome-wide meta-analysis further found that studying the relationship between phytosterols and coronary artery disease in six studies with 9,758 subjects, ten independent genome-wide significant SNPs at seven genomic loci were detected. A positive causal association was found between plasma sitosterol concentration and coronary artery disease. The clinical significance of this signal for supplementation at normal doses in non-sitosterolemia individuals remains debated.
Concerns have been raised regarding the potential of phytosterols to impair absorption and status of fat-soluble vitamins. Particular consideration is given to the observed lowering effect of phytosterols on plasma concentrations of carotenoids, especially of β-carotene (e.g., in the range of up to 20% decrease observed with ingestion over one year of 20 g/day of products containing 8% phytosterols). Although the health effects of chronically low blood carotenoid concentrations are largely unknown, there could be cause for concern during developmental phases when requirements are higher than normal, such as during pregnancy, lactation, or infancy. For this reason, EFSA labelling requirements for phytosterol-enriched products include the need to indicate that the product should be used as part of a healthy diet including regular consumption of fruit and vegetables to help maintain carotenoid levels.
Contraindications include those without hyperlipidaemia, children under the age of five, and pregnant or breastfeeding women who are not under close medical supervision. EFSA also requires labelling to state that patients on cholesterol-lowering medication should only consume phytosterol products under medical supervision.
There is controversy about treatment with statins inducing a further increase in plasma non-cholesterol sterols, raising concerns about the safety of supplementation of plant sterols to such drugs. Conversely, phytosterols can also benefit people taking statins or ezetimibe, a cholesterol-lowering drug. The net clinical implication of the sterol-raising effect of statins combined with phytosterol supplementation is not yet clearly resolved.
Phytosterol bioavailability is a key issue, as it can be influenced by several factors (type, source, processing, preparation, delivery method, food matrix, dose, time of administration, and genetic factors), and the existence of a close relationship between their chemical structures — e.g., saturation degree and side-chain length — and low absorption rates has been established.
Health conditions that Alpha phytosterol may help support.
Body systems that Alpha phytosterol may help support.
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