Adverse effects of conjugated linoleic acids supplementation on circulating lipoprotein (a) levels in overweight and obese individuals: results of a systematic review and meta-analysis of randomized controlled trials

Conjugated Linoleic Acids (CLA) may have beneficial effects on the prevention of atherosclerosis, but their net effects on circulating levels of lipoprotein (a) [Lp (a)] are unclear. The present study aimed to systematically review and analyze the Randomized Clinical Trials (RCTs) assessing the effects of CLA on circulating Lp (a) concentrations. A literature search of SCOPUS, PubMed-Medline, ISI, Web of Science, and Cochrane library databases was conducted for the relevant RCTs investigating the effects of CLA supplementation on circulating Lp (a) levels, which had been published up to 20 August 2020. Weighted Mean Difference (WMD) and 95% Confidence Intervals (CI) were reported as the summary statistics. Statistical analysis were done with Comprehensive Meta-Analysis (CMA) V2 software (Biostat, NJ). Totally, six studies with 13 treatment arms including 752 subjects were included in the meta-analysis. The results showed a significant increase in circulating Lp (a) levels after CLA supplementation (WMD: 16.68 mg/L, 95% CI: 5.43-27.93; P=0.004) with no evidence of heterogeneity across the studies. In the subgroup analysis, a more significant elevation of Lp (a) levels was observed in the trials lasting for six months or more (WMD: 21.61 mg/L, 95% CI: 9.85-33.37, P<0.001) as well as in those with a supplementation dosage of ≥3.5 g/d (WMD: 26.13 mg/L, 95% CI: 7.02-45.24, P=0.007). These findings were sensitive to one study. It can be concluded that CLA supplementation with a dose of ≥3.5 g/d over a six-month period might significantly increase the circulating Lp (a) concentrations.