Selected studies 2000–2004
Hallikainen et al. [37] showed that in normal to mildly hypercholesterolemic men and women, 0.8 g of free tall/ vegetable stanol equivalents in spreads decreased LDL non-significantly by only 1.6%. This 0.8 g dose did reduce the number of apo B particles by 8.7%, indicating a reduced number of LDL particles. Similar to Vanhanen et al. [32], the higher dose of 1.6 g of stanol equivalents reduced LDL cholesterol to a greater extent of 6.1%, and two higher doses (2.4 and 3.2 g/d) reduced LDL cholesterol 10.6–11.5%. The three higher doses (1.6–3.2 g/d) lowered LDL cholesterol in a statistically significant manner. A caveat in this study was that the 0.8 g/d dose was given after cholesterol was already lowered by 3 subsequent plant sterol treatments, possibly producing bias against seeing a reduction in LDL cholesterol with 0.8 g/d. Albeit the above experimental weakness, the conclusion would be that the dose of 1.6 g/d of stanol equivalents is a more optimal dose for LDL cholesterol reduction.
Maki et al. [38] administered mildly hypercholesterolemic men and women 1.1 g/d of free tall sterol equivalents in spreads, fed as sterol esters in two doses, which decreased LDL levels by 4.9% while 2.2 g/d of sterol equivalents decreased LDL by 5.4%.
Christiansen et al. [39] reported an 11.3% reduction in LDL cholesterol after 6 months with 1.5 g/d of microcrystalline free sterols in spreads. No additional improvement was seen with 3.0 g/d of plant sterol.
Volpe et al. [40] reported a 6.3% placebo-adjusted decrease in LDL cholesterol after 4 wks with 1.0 g/d and a greater reduction of about 12.2% with 2 g/d after 4 wks. De Graaf et al. [105] found an intake of 1.8 g/d of free sterols in chocolates to decrease LDL cholesterol 8.9% relative to baseline.
Thomsen et al. [42] examined effects of non-esterified, non-hydrogenated, soy bean derived plant sterols, solubilized in a partly vegetable oil filled low fat milk on serum LDL cholesterol in 81 mildly hypercholesterolemic Danish patients, in a double-blind, randomised, placebo-controlled 3-arm cross-over study. Subjects consumed habitual diets, with some restrictions on consumption of fat and cholesterol rich foods. Subjects received 0, 1.2, or 1.6 g/d of sterols in two servings of 250 mL milk for 12 wks (4 wks/dose). The placebo-adjusted mean reduction in LDL was 7.1 ± 12.3 and 9.6 ± 12.4% (mean ± SD) for groups receiving 1.2 and 1.6 g of plant sterols, respectively, with no differences between sexes. There was no statistically significant difference in LDL lowering amongst the 1.2 and 1.6 g/d groups, although Apo B was decreased more with 1.6 than 1.2 g/d of sterols. Apo B is an index of LDL particle number, thus the higher dose may have decreased numbers of LDL particles more than the lower dose. Differences in numbers of small, dense, atherogenic LDL particles and LDL oxidization [43] are other important future parameters to assess. It is noteworthy that there were 20–23% non-responders in the two sterol groups, which was partially consistent with the large differences in cholesterol absorption inhibition observed with similar milk products containing plant sterols [44]. Thus, renewed attention should be given to the issue of non-responders. Another noteworthy observation was the randomization order in which the three milk products affected the magnitude of the LDL lowering results, but not the overall statistical findings. The placebo-adjusted mean percentage decrease in LDL was more pronounced with certain randomixation sequences compared to others. This consideration is typically ignored in reporting results of plant sterol clinical trials examining cholesterol lowering efficacy.
In a very recent study still in press [45], 72 men and women aged 20–73 received two 8 ounce servings of Minute Maid brand non-fat orange juice with breakfast and dinner meals, providing 2 g/d of Cargill CoroWise plant sterols for 8 wks. LDL was reduced 12.4% compared to baseline and placebo; HDL and triacylglycerol levels were not changed. The authors speculate that the fat in the meals may help to emulsify the plant sterols in the orange juice.
Effects of naturally occurring plant sterols
The effects of naturally-occurring plant sterols on cholesterol metabolism have also been studied in both older and more recent literature. It was reported that the differences between effects of different plant oils on blood lipid profiles may be related to their content of plant sterols [46-49]. Indeed, there has been renewed interest in the cholesterol lowering properties of speciality grains and unprocesses oils rich in plant sterols including amaranth oil [50,51], rice bran oil [52] (Berger et al., submitted), avocado oil [53], extra virgin olive oil [54], macadamian nut [55], and argan oil [56].
Ostlund et al. [49] showed that doses as low as 150–300 mg of naturally present corn oil-derived phytosterols can reduce dietary cholesterol absorption. Also, it was shown that the consumption of original wheat germ, which contains about 328 mg plant sterols, reduced the cholesterol absorption by 42.8 % compared to plant sterol-free wheat germ [57]. These results indicate that naturally available plant sterols are biologically effective as plant sterol supplementation in reducing cholesterol absorption, and that natural plant sterols have important effects on cholesterol metabolism [57].