Anti-inflammation activity of plant sterols

Bouic [17] and Bouic et al [164] have reviewed the possible roles of phytosterols in the etiology or preventive role of phytosterols in various diseases and conditions, including proliferative responses of lymphocytes, pulmonary tuberculosis, feline immunodeficiency virus and HIV, stress induced immune suppression, rheumatoid arthritis, and allergic rhinitis/sinusitis. The mechanisms by which plant sterols display their anti-inflammatory activity are thought to include inhibition of secretion of inflammatory mediators such as interleukin-6, and tumor necrosis factor-α by monocytes [17]. Most of the work has been conducted with animals. From these provocative results, it is not unlikely that plant sterols will be further used for purposes related to control of deveopment and spread of certain cancers in humans.

Anti-oxidant activity

Another possible effect of plant sterols is their antioxidant activity [165]. It was found that the methanol extract of soybean oil, which has a strong in-vitro protective effect against DNA damage in human endothelial cell, contains phytosterols in addition to tocopherols and n-3 polyunsaturated fatty acids (PUFA). Results suggest that the antioxidant activity of soybean oil may be in part related to sterol content. Moreover, in in-vitro conditions, sitosterol, and sitosterol glucoside were found to decrease lipid peroxidation of platelet membranes in the presence of iron [18] and in healthy human subjects a 2 and 3-g dose of stanol ester reduced oxidized LDL-C levels [82]. The authors suggested that the intake of stanol ester might protect LDL particles from oxidation. Thus, based on results from in vitro studies and on human study, there is a possibility that plant sterols may possess antioxidant properties. Such antioxidant protection could also benefit atherosclerosis [166] and cancer [167] disease state.

Anti-ulcer activity

In a recent study, phytosterol esters, but not sterols, in horse gram (an herb in the genus Dolichos cultivated in India for food and fodder) were protective in a pyloric ligation model of ulcer, whereas sterols were protective in acute ulcer models using ethanol-induced and cysteamine-induced ulceration [168]. Phospholipids were protective in both types of model. Thus, the presence of sterols, sterol esters, and phospholipids in food lipids in staple diets may account for the low prevalence of duodenal ulcer in certain geographical areas, despite a uniformly high prevalence of Helicobacter pylori infection.

Anti-fungal activity

Another area for future investigation is the anti-fungal activity of plant sterols and related triterpenes [169]. In this work, the anti-fungal activity of triterpenes in the mushroom species Ganoderma annulare was demonstrated.


It has been concluded that plant sterols, within the range that causes desirable reduction in blood levels of total cholesterol and LDL-cholesterol, are clinically safe. This conclusion has been reported in short-term studies [19,39,40,170] as well as in long-term study that lasted for 1 year [81]. Since plant sterols decrease the absorption of cholesterol, they might also affect the absorption of fat-soluble vitamins. The scientific evidence for the impact of phytosterols on carotenoid status and fat soluble vitamins is summarized in Table 3. The effect of plant sterols on the blood levels of precursors of fat-soluble vitamins is a controversial issue. In some studies, plant sterols consumption has been shown to significantly reduce levels of carotenoids [25,37,38,81,170,171], tocopherol [37], and lycopene [25,38]. Other studies reported that the consumption of plant sterols does not affect blood levels of carotenoids [39,72,104,172], tocopherol [19,39,173], and lycopene [19,173].

In a recent trial comparing equal free sterol equivalent amounts (2.2 g/d) of esterified sterols and free sterols in milk, both forms of sterols decreased the absorption of β-carotene and α-tocopherol in normocholesterolemic men. The reduction in β-carotene bioavailability was significantly less pronounced with free plant sterols than with plant sterol esters However, there was no difference in cholesterol absorption between the two forms of plant sterols. [71]. Esters are presumed to have more of an effect on fat soluble vitamins because they partition into the oil phase of the intestine, whereas free sterol would partition into the micellar phase [174].

During plant sterol consumption, increasing the consumption of fruits and vegetables to be > five servings and including one or more carotenoid rich source would be enough to avoid reduction in carotenoid levels resulted from plant sterol intake [106].