Effect of plant sterol-enriched margarine on plasma lipids and sterols in subjects heterozygous for phytosterolaemia

Abstract

Abstract. Stalenhoef AFH, Hectors M, Demacker PNM (University Medical Centre Nijmegen, Nijmegen, The Netherlands). Effect of plant sterol-enriched margarine on plasma lipids and sterols in subjects heterozygous for phytosterolaemia. J Intern Med 2001; 249: 163–166.

Objective. Margarine with added plant sterols lowers plasma cholesterol levels. It is of importance to know whether these margarines can be used safely in carriers of a hereditary disorder with increased absorption of plant sterols.

Design. In an open feeding study of 8 weeks with a 2-week run-in period and 2 final weeks as a washout period on control margarine (0.3% plant sterols), two obligate heterozygous parents of a patient with classical sitosterolaemia were subjected for 4 weeks to a diet containing margarine enriched with plant sterols (8%). Fasting blood samples were taken weekly. Primary outcomes were plasma lipid and lipoprotein levels and plant sterol levels.

Results. Both parents were hyperlipidaemic. Total plasma cholesterol levels were decreased by 11 and 12%, respectively, after 4 weeks of the consumption of 40 g day⁻¹ of plant sterol-enriched margarine. This was mainly due to changes in LDL-cholesterol, whereas the other lipoproteins, including lipoprotein(a), were unaffected. Total plant sterol levels increased maximally 139% from 0.31 to 0.82% of total sterols in the father, and maximally 83% from 0.32 to 0.66% of total sterols in the mother.

Conclusion. An intake of around 3 g day⁻¹ of plant sterols by subjects heterozygous for phytosterolaemia increased campesterol or sitosterol levels in blood to similar levels as found in normal subjects. In addition, plasma cholesterol levels were reduced to the same extent as in normal or hypercholesterolaemic individuals.

Introduction

Phytosterolaemia (also known as sitosterolaemia) is a rare, recessively inherited disorder characterized by extremely high plasma levels of plant sterols, xanthomas and premature coronary heart disease [1]. Under normal circumstances, the Western diet contains almost equal amounts of cholesterol and plant sterols. However, 30–60% of total dietary cholesterol and only <5% of total plant sterols are normally absorbed in the gut [2]. Affected patients have uncontrollable sterol absorption, higher plasma and tissue cholesterol and phytosterol concentrations and low endogenous cholesterol synthesis [3]. Lowering dietary cholesterol and plant sterol intake is one of the first obvious approaches. Heterozygous carriers of this disorder are clinically and biochemically normal [4].

Recently, a new cholesterol-lowering spread has been introduced that contains 8% of plant sterols (Becel pro-aktiv^®, Unilever, Vlaardingen). Such a concentration will increase the individual daily intake of plant sterols by five- to 10-fold [5]. Thus, the question arises about the impact of such elevated intake of plant sterols on subjects heterozygous for phytosterolaemia. We therefore investigated the effect of feeding margarine enriched with plant sterols on plasma lipoproteins and sterols in two heterozygous parents of a patient with classical phytosterolaemia.

Materials and methods

The proband (female, age 28 years) was identified at 16 years old on the basis of the presence of tendon and tuberous xanthomas and extremely high (50- to 100-fold increased) plasma sterol levels [4]. Her parents participated in this study. They were both 52 years of age, hypercholesterolaemic and obese (BMI, 33.9 and 35.0 kg m⁻², respectively). The feeding study consisted of 8 weeks with a 2-week run-in period and 2 final weeks as a washout period. They first consumed control margarine (40 g day⁻¹, 35% fat and 0.3% plant sterols) for 2 weeks; after that they consumed the margarine enriched with plant sterols (8.2%) with no modification to their usual diet. Fatty acid composition of both margarines was similar (48% polyunsaturated fatty acids). The chemical composition of the margarines has been described in detail [5]. Blood samples were collected at −2, 0, 1, 2, 3, 4 and 6 weeks. Subjects gave signed written informed consent. Full-week dietary records were filled out by the two subjects. Compliance evaluated by counting the tubs was 100%; the body weights did not change during the study period.

Plasma cholesterol and triglycerides were determined enzymatically in fasting samples. High-density lipoprotein (HDL) cholesterol was determined by the phosphotungstic acid/Mg²⁺ precipitation method [6]. Very low density cholesterol (VLDL) was isolated by ultracentrifugation at d=1.006 g mL⁻¹ (Beckman, Palo Alto, CA). LDL cholesterol was calculated by subtraction. ApoB and apoA1 were quantified by immunonephelometry [7]. Lipoprotein(a) was measured by a specific radioimmunoassay (Mercodia AB, Uppsala, Sweden). Plant sterol levels were measured using gas chromatography following established methodology [8, 9]. Briefly, 0.1 mL plasma was saponified with KOH for 1 h at 37 °C. Extracted samples were derivatized with BSTFA/1% TMCS and injected into a Varian 3400 gas chromatograph (Sunnyvale, CA) equipped with a flame ionization detector and a data processing system, using coprostanol as an internal standard. Campesterol, stigmasterol and sitosterol were identified using authenticated standards (Sigma, St Louis, MO).

Results

The father exhibited mixed hyperlipidaemia, which was known for several years; the mother was also hypercholesterolaemic (Table 1). The consumption of plant sterol-enriched margarine did not cause side-effects. Total plasma cholesterol levels were decreased by 11 and 12% in the parents, respectively, after 4 weeks of the consumption of 40 g day⁻¹ plant sterol-enriched margarine (Table 1). This was mainly due to changes in LDL cholesterol, whereas the other lipoproteins, including Lp(a) were unaffected. The decrease in apoB was in the same order as that in serum cholesterol. Total plant sterol levels increased maximally 139% from 0.31 to 0.82% of total sterols in the father, and maximally 83% from 0.32 to 0.66% of total sterols in the mother (Table 2). After 3 weeks of consumption of plant sterols, their blood levels seemed to have reached equilibrium with no further increase. In 33 healthy control subjects, fasting plasma campesterol levels on their normal diet ranged from 3.8 to 24.2 μmol L⁻¹ (mean 13.1) and plasma sitosterol from 2.1 to 16.5 μmol L⁻¹ (mean 8.9).

Table 1.  Plasma lipids, lipoprotein and apolipoprotein levels and lipoprotein(a) in heterozygous subjects consuming margarine enriched in plant sterols

Table 2.  Plasma total cholesterol and plant sterol in heterozygous subjects consuming margarine enriched in plant sterols

Discussion

Daily intake of plant sterol-enriched margarine lowered blood total cholesterol levels in the subjects heterozygous for phytosterolaemia by an average of 10.2 and 11.0%, respectively (average of weeks 3 and 4). This is in accordance with what has been reported earlier in normal and hypercholesterolaemic subjects [5, 10]. Of importance in this study was that an intake of around 3 g day⁻¹ of plant sterols in the heterozygotes did not increase campesterol or sitosterol levels in blood to levels higher than reported in normal subjects consuming similar margarine [11, 12]. In addition, the increase in blood plant sterols observed in the two heterozygotes was slightly higher than observed in our healthy subjects on a normal diet and was less than 1% of blood total sterols. After 3 weeks of a steady consumption of plant sterols, blood levels of the subjects seemed to have reached equilibrium without further increase, but long-term follow-up studies are necessary to confirm this.

In conclusion, plant sterol-enriched margarine appears to be as efficacious in reducing cholesterol in subjects heterozygous for phytosterolaemia as in normal or hyperlipidaemic subjects, without strong accumulation of plant sterols in their plasma. As pointed out by Law [13], consumption of margarines containing plant sterols as well as stanols can be expected to reduce the risk of heart disease of about 25%.

Acknowledgements

This study was supported by Unilever Research, Vlaardingen, The Netherlands. Unilever also provided the margarines.