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74 CPD ACTIVITY FROM PAGE 73 in the small intestine2. This increase in hepatic cholesterol stimulates very low- density lipoprotein (VLDL) secretion and hence LDL formation, and down-regulates hepatic LDL receptor activity that elevates circulating LDL-C levels2. It’s known that VLDL remnants and LDL can deliver cholesterol to the artery wall, initiating or exacerbating atherosclerosis.2 Plant sterols such as sitosterol and campesterol are bioactive components with similar functions to those of cholesterol in mammals.2 Plant sterols differ from cholesterol in the structure of their side chains. Plant stanols are 5 alpha-saturated derivatives of plant sterols2 (see Figure 1). These compounds affect luminal cholesterol absorption.2 Plant sterols cause a significant inhibition of cholesterol absorption in the small intestine through disruption of the intraluminal solubilisation step.2 This is the essential step for the absorption of cholesterol into the absorptive cell and subsequently into the circulation. Plant sterols dilute the pool of cholesterol in the intestine and compete with cholesterol for the available absorption capacity.2 They are also absorbed to a lesser extent than cholesterol, with only about five per cent of plant sterols and stanols absorbed by the intestine.2 Plant sterols are found naturally in foods. In the typical Western diet, the mean daily intake of plant sterols is about 300mg. Intake can be higher in vegetarians.2 There are foods enriched with plant sterols and plant sterol supplements that claim to reduce total cholesterol (see Figure 2). The most recent meta-analysis by Ras et al3, examined 124 studies where supplementary plant sterols were given at a mean daily dose of 2g. They concluded that both plant sterols and stanols are effective at lowering LDL cholesterol by on average 12 per cent when consuming plant sterol enriched foods with sterol/stanol doses of up to 3g per day. Plant sterols should be consumed with a main meal for best results.4 Psyllium husk supplementation Psyllium is a soluble fibre from the husk of the Plantago ovata seed native to India. Psyllium owes its therapeutic properties to its mucilage content,5 Commonly used as a stool-bulking agent for the treatment of constipation, these are a group of clear, colourless gelling agents present in the refined white fibrous material of the seed.5 The hydrophilic nature of these agents absorbs water to form a clear colourless gel that increases the volume of the solution in excess of 10 times.5 The cholesterol lowering effects of psyllium husk is thought to largely be related to binding bile acids in the small intestine.5 Bile acids are synthesised in the liver from cholesterol and secreted into the small intestine. Bile acids are reabsorbed in the ileum and recycled back to the liver for further secretion into the small intestine by the enterohepatic circulation, and consequently this causes a decrease in the rate of synthesis of the bile acids.5 The soluble fibre gel of the psyllium binds bile acids in the small intestine, preventing the reabsorption of the bile acid from the small intestine and increasing their faecal excretion.5 Collectively, this results in an increase of cholesterol uptake from the circulation by the liver to produce bile acids, replacing the bound acids and decreasing serum cholesterol in the process.5 A 2018 systematic review and meta- analysis of randomised controlled trials examined the effect of psyllium on LDL Figure 1. Chemical structure of common plant sterols and stanols.2 RETAIL PHARMACY • AUG 2020