Effects of carotenoid supplementation on glycemic control: a systematic review and meta-analysis of randomized clinical trials

ObjectivesWe conducted a systematic review and meta-analysis to assess the effects of carotenoid supplementation on glycemic indices, and the certainty of evidence.MethodsA systematic literature search in PubMed, SCOPUS, ISI-Web of Science, and Cochrane Library was conducted from inception up to Jun 17, 2024. Randomized controlled trials (RCTs) investigating the effect of carotenoid supplementation on circulating glycemic parameters were included. Records were excluded when studies reported the effect of co-interventions with other nutrients, did not provide mean differences (MDs) and standard deviations (SD) for outcomes, or administered whole food rather than supplements of carotenoids. Summary mean differences (MDs) and 95% CI between intervention and control groups were estimated using a random-effects model. The risk of bias of the included studies was assessed using the Risk of Bias 2.0 (RoB 2.0) tool.ResultsOverall, 36 publications with 45 estimated effect sizes were included in the meta-analyses. The overall findings showed an improvement in fasting blood glucose (FBG) (MD = -4.54 mg/dl; 95% CI: -5.9, -3.2; n = 45), and hemoglobin A1C (HbA1C) (MD = -0.25% (95% CI: -0.4, -0.11; n = 22) in the intervention group in comparison with the control group. Moreover, in individuals with type 2 diabetes (T2D), interventions with astaxanthin and fucoxanthin led to a reduction in FBG by 4.36 mg/dl (95% CI: -6.13, -2.6; n = 10). The findings also showed that the intervention with crocin reduced FBG levels by 13.5 mg/dl (95% CI: -15.5, -7.8; n = 5), and HbA1C by 0.55% (95% CI: -0.77, -0.34; n = 5) in individuals with T2D. However, the certainty of evidence was very low.ConclusionCarotenoid's supplementation improved glycemic parameters especially in people with T2D. However. the certainty of evidence was very low, mainly due to small sample size, and indirectness. Therefore, no specific recommendations can be provided at present and well-designed RCTs are required.Registry URLhttps://www.crd.york.ac.uk/PROSPERO/Registry numberCRD42021285084Registry and registry number for systematic reviews or meta-analysesPROSPERO ID: CRD42021285084