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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-.

Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet].

Vitamin C supplementation lowers serum low-density lipoprotein cholesterol and triglycerides: a meta-analysis of 13 randomized controlled trials

MP McRae.

Review published: 2008.

CRD summary

The review concluded that supplementation with at least 500mg/day of vitamin C for at least four weeks can result in significant decreases in low-density lipoprotein cholesterol and triglyceride; there was a non-significant elevation of serum high-density lipoprotein cholesterol. A lack of study quality assessment and other methodological problems limited the reliability of the author’s conclusions.

Authors' objectives

To investigate the effects of vitamin C supplementation on low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol and triglycerides in patients with hypercholesterolaemia.

Searching

MEDLINE was searched from 1970 to June 2007 for published full-length journal articles in any language. Search terms were reported. Manual searches of review articles and retrieved papers were conducted.

Study selection

Randomised controlled trials (RCTs) in participants with hypercholesterolaemia (total serum cholesterol >200mg/dL) who received oral vitamin C supplementation (at least 500mg/day) compared with control were eligible for inclusion. Trial interventions had to be given for between four and 24 weeks. Trials had to report outcomes on mean LDL cholesterol, HDL cholesterol or triglyceride changes in both treatment and control groups.

The included trials evaluated vitamin C at a dose of between 500mg/day and 2,000mg/day given for between four and 24 weeks. Baseline LDL cholesterol ranged from 121mg/dL to 220mg/dL, baseline HDL cholesterol ranged from 33mg/dL to 60mg/dL and baseline triglyceride ranged from 151mg/dL to427 mg/dL. The proportion of males varied from zero to 100%. Mean age ranged from 48 to 82 years.

The author did not state how many reviewers were involved in study selection.

Assessment of study quality

The author did not state that they assessed validity.

Data extraction

Data was extracted on the pre- and post-treatment LDL cholesterol, HDL cholesterol and triglycerides and used to calculate net changes and 95% confidence intervals (CIs).

The author did not state how many reviewers were involved in data extraction.

Methods of synthesis

A random-effects meta-analysis was undertaken, which pooled net changes for LDL cholesterol, HDL cholesterol and triglycerides. Publication bias was assessed using funnel plot analysis.

Results of the review

Thirteen RCTs were included in the review: five cross-over trials and eight parallel design trials (number of participants unclear). Trial sample sizes ranged from 18 to 138 participants.

Compared with control, the vitamin C supplementation group had a statistically significantly lower net change in LDL cholesterol (net change -7.90, 95% CI -12.3 to -3.5; n=638 participants), total cholesterol (net change -10.67, 95% CI -14.0 to -7.3; n=1,119 participants) and triglycerides (net change -20.1, 95% CI -33.3 to -6.8; n=555 participants). There was a non statistically significant increase in HDL cholesterol (net change 1.1, 95% CI -0.2 to 2.3; n=692 participants).

Funnel plot assessment showed no evidence of publication bias for any of the outcomes apart from HDL cholesterol.

Authors' conclusions

Supplementation with at least 500mg/day of vitamin C for a minimum of four weeks can result in significant decrease in LDL cholesterol and triglyceride concentrations; there was a non-significant elevation of serum HDL cholesterol.

CRD commentary

Inclusion criteria for the review were clearly defined; one relevant database was searched and manual searches were undertaken. Publication bias was assessed and was not detected except in the analysis of HDL cholesterol. The author attempted to minimise language bias by including articles in any language. It appeared that there were no attempts to minimise reviewer error and bias during study selection and data extraction. Quality assessment was not reported. The author acknowledged that many of the trials had small sample sizes. There were differences in trial duration, dosages and participant characteristics, which the author recognised and did not explore further. Trial outcomes were assessed using random-effects meta-analysis. Statistical heterogeneity was not discussed.

Overall, the lack of quality assessment and analysis of statistical heterogeneity and the small sample sizes of the included trials limit the reliability of the author’s conclusions.

Implications of the review for practice and research

The author did not state any implications for practice and further research.

Funding

Not stated.

Bibliographic details

McRae MP. Vitamin C supplementation lowers serum low-density lipoprotein cholesterol and triglycerides: a meta-analysis of 13 randomized controlled trials. Journal of Chiropractic Medicine 2008; 7(2): 48-58. [PMC free article: PMC2682928] [PubMed: 19674720]

Indexing Status

Subject indexing assigned by CRD

MeSH

Ascorbic Acid; Cholesterol, HDL; Cholesterol, LDL; Humans; Hypercholesterolemia; Triglycerides

AccessionNumber

12008107317

Database entry date

02/02/2011

Record Status

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.

CRD has determined that this article meets the DARE scientific quality criteria for a systematic review.

Copyright © 2014 University of York.

PMID: 19674720

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