This review assessed the effect of psyllium on cholesterol levels in patients with mild to moderate hypercholesterolaemia. The authors concluded that psyllium produced a dose- and time-dependent serum cholesterol lowering effect in these patients and could be a useful adjunct to dietary therapy. Because of a lack of study quality assessment, the authors’ conclusions should be interpreted with caution.

To determine the dose-response relationship between psyllium and serum cholesterol level and the time-dependent effect of psyllium in individuals with mild to moderate hypercholesterolaemia.

MEDLINE, EMBASE, BIOSIS Previews and Pascal (1966 to August 2005) were searched for relevant studies. Search terms were reported. Food and Drug Administration documents, published reviews, reference lists of relevant trials and conference abstracts were searched.

Studies were eligible if they were randomised controlled trials of psyllium treatment in adults with mild to moderate hypercholesterolaemia. Studies had to have a minimum duration of treatment of two weeks and to provide outcomes for change in lipid parameters in intervention and control groups. Background treatment had to be low fat diet or controlled usual diet. Studies of hypercholesterolaemia secondary to any recognised cause were excluded.

Included studies were conducted in USA, UK, Canada, Australia and Mexico. A quarter of the trials were cross-over trials. Participants had initial total cholesterol levels of greater than 4.78mmol/L or LDL cholesterol levels of greater than 3.36mmol/L. Most studies had a dietary lead-in period. Most studies used a low fat diet or an NCEP (National Cholesterol Education Program) step 1 or step 2 diet as background diet; four used a controlled usual diet. About half of the studies used bulk laxatives and half used psyllium-enriched foods. Doses of psyllium ranged between 3g/day and 20.4g/day. Treatment periods ranged from 14 to 182 days.

The authors did not state how many reviewers performed the selection. Disagreements on inclusion were resolved by discussion and consensus.

The authors did not state that they assessed validity.

Two reviewers independently extracted data. Disagreements were resolved by discussion with a third reviewer.

Lipid parameters were reported in mmol/L (converted from mg/dL if necessary). For parallel group trials, mean change (baseline minus endpoint values) in the control group was subtracted from that in the intervention group. For crossover studies, effect size was calculated as difference of post-treatment lipid concentrations of treatment and control periods.

Pooled effect sizes and 95% confidence intervals were estimated using fixed-effect and random-effects models based on the technique by Anne (2002). Heterogeneity was assessed using the Cochrane Q test. Subgroup analyses were performed for psyllium dose (10.2g/day), background diet (step I diet), use of psyllium-enriched foods, treatment period (eight weeks), design type (parallel trial) and trial conducted in USA. Meta-regression was used for comparing the difference between psyllium-enriched foods and bulk laxative and for exploring a dose-response relationship (only parallel trials used for the dose-response evaluation). When more than one dose of psyllium was used, mean lipid change across all doses was used to provide an average effect size. The long-term effect of psyllium was explored using a mixed-effects model for repeated measure data. Funnel plot analysis was used to detect publication bias (Egger test).

Twenty-one trials (n=1,717) were included.

Psyllium significantly reduced total serum cholesterol by 0.375mmol/L (95% CI 0.257 to 0.494) and LDL cholesterol by 0.278mmol/L (95% CI 0.213 to 0.312). HDL cholesterol was significantly reduced, but only by a small amount (0.0353 mmol/L, 95% CI 0.0003 to 0.0514). There was no significant effect on triglycerides. There was significant heterogeneity for the analysis of total cholesterol and some small study bias could be detected (p=0.04 for LDL cholesterol).

For both total cholesterol and LDL cholesterol reduction with psyllium, there was a significant dose-response relationship. Both total cholesterol and LDL cholesterol continued to decrease over time; LDL cholesterol decreased more slowly than total cholesterol. There was no significant difference in treatment effect when psyllium given as bulk laxatives was compared with psyllium-enriched foods. No significant differences in treatment effect were seen for any subgroups.

Psyllium produced a dose- and time-dependent serum cholesterol lowering effect in patients with mild and moderate hypercholesterolaemia and could be useful as an adjunct to dietary therapy in treating hypercholesterolaemia.

This systematic review addressed a clear research question and was supported by appropriate inclusion criteria. The literature search included relevant databases, but only limited search terms were reported and the date of the latest search was four years before publication (so newer studies may have been overlooked). Additional searches were performed to supplement the electronic search. No assessment of study quality was reported and so validity of the included studies was unclear. Both study selection and data extraction were performed by two independent reviewers. Included studies tended to be short duration; most lasted no longer than two months. Many studies had a small sample size. Only limited details on included patients were provided. Because of the lack of quality assessment of studies, the authors’ conclusions should be interpreted with caution.

The authors made no specific recommendations for research and practice.

Partially supported by the Cooperative Programme of the Rhone-Alps region and Shanghai.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.