title: Systematic review and meta-analysis of randomised controlled trials testing the effects of vitamin C supplementation on blood lipids.
abstract: Randomised controlled trials (RCTs) in humans revealed contradictory results regarding the effect of vitamin C supplementation on blood lipids. We aimed to conduct a systematic review and meta-analysis of RCTs investigating the effect of vitamin C supplementation on total cholesterol, low-density lipoprotein-cholesterol (LDL-C), high-density lipoprotein-cholesterol (HDL-C) and triglycerides and to determine whether the effects are modified by the participants' or intervention characteristics.
  
  
  
  Four databases (PubMed, Embase, Scopus and Cochrane Library) were searched from inception until August 2014 for RCTs supplementing adult participants with vitamin C for ≥ 2 weeks and reporting changes in blood lipids.
  
  
  
  Overall, vitamin C supplementation did not change blood lipids concentration significantly. However, supplementation reduced total cholesterol in younger participants (≤52 years age) (-0.26 mmol/L, 95% CI: -0.45, -0.07) and LDL-C in healthy participants (-0.32 mmol/L, 95% CI: -0.57, -0.07). In diabetics, vitamin C supplementation reduced triglycerides significantly (-0.15 mmol/L, 95% CI: -0.30, -0.002) and increased HDL-C significantly (0.06 mmol/L, 95% CI: 0.02, 0.11). Meta-regression analyses showed the changes in total cholesterol (β: -0.24, CI: -0.36, -0.11) and in triglycerides (β: -0.17, CI: -0.30, -0.05) following vitamin C supplementation were greater in those with higher concentrations of these lipids at baseline. Greater increase in HDL-C was observed in participants with lower baseline plasma concentrations of vitamin C (β: -0.002, CI: -0.003, -0.0001).
  
  
  
  Overall, vitamin C supplementation had no significant effect on lipid profile. However, subgroup and sensitivity analyses showed significant reductions in blood lipids following supplementation in sub-populations with dyslipidaemia or low vitamin C status at baseline. PROSPERO Database registration: CRD42014013487, http://www.crd.york.ac.uk/prospero/.
authors.affiliation: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle on Tyne NE4 5PL, UK; College of Medicine, University of Al-Mustansiriyah, Baghdad, Iraq. Electronic address: a.w.ashor@ncl.ac.uk.
authors.forename: Ammar W
authors.initials: AW
authors.lastname: Ashor
authors.affiliation: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle on Tyne NE4 5PL, UK; MRC Human Nutrition Research, Elsie Widdowson Laboratories, 120 Fulbourn Road, Cambridge CB1 9NL, UK.
authors.forename: Mario
authors.initials: M
authors.lastname: Siervo
authors.affiliation: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle on Tyne NE4 5PL, UK.
authors.forename: Femke
authors.initials: F
authors.lastname: van der Velde
authors.affiliation: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle on Tyne NE4 5PL, UK.
authors.forename: Naomi D
authors.initials: ND
authors.lastname: Willis
authors.affiliation: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle on Tyne NE4 5PL, UK.
authors.forename: John C
authors.initials: JC
authors.lastname: Mathers
mesh_terms: D000975:Antioxidants / Q000627:therapeutic use*; D001205:Ascorbic Acid / Q000627:therapeutic use*; D001206:Ascorbic Acid Deficiency / Q000178:diet therapy / Q000503:physiopathology / Q000517:prevention & control; D002317:Cardiovascular Agents / Q000627:therapeutic use; D002318:Cardiovascular Diseases / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control; D050171:Dyslipidemias / Q000178:diet therapy* / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D006801:Humans; D006949:Hyperlipidemias / Q000178:diet therapy / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D000960:Hypolipidemic Agents / Q000627:therapeutic use*; D018384:Oxidative Stress; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results; D012306:Risk
chemical_list: D000975:Antioxidants; D002317:Cardiovascular Agents; D000960:Hypolipidemic Agents; D001205:Ascorbic Acid
keywords: Ascorbic acid; Cardiovascular risk; Cholesterol; Lipoproteins; Nutritional supplements; Triglycerides