A systematic review of dietary and circulating carotenoids and liver disease

Background: due to the high incidence of liver disease and the severity of adverse outcomes, liver disease has become a serious public health problem, bringing a huge disease burden to individuals, families, and society. Most studies have shown significant differences in serum carotenoid content and dietary carotenoid intake between liver disease patients and non-liver disease patients, but some studies have reported contrary results. This paper aimed to systematically review and analyze all published epidemiological studies on carotenoids and liver disease to quantitatively assess the relationship between serum and dietary carotenoid concentrations and liver disease. Methods: by systematically searching PubMed, Web of Science, Scopus, Embase, and Cochrane databases according to pre-combined search terms from inception to July 23, 2024, 30 studies were found to meet the exclusion criteria. Finally, 3 RCT studies, 6 cohort studies, 11 case-control studies, 9 cross-sectional studies, and 1 RCT-combined cross-sectional study were included in the further analysis. Two reviewers independently scored the literature quality and extracted data, and the results were represented by the standard mean difference (SMD) with a 95% confidence interval. Cochran Q statistics and I² statistics were used to evaluate statistical heterogeneity (defined as significant when P < 0.05 or I² > 50%). When there was insignificant heterogeneity, a fixed effects model was selected; otherwise a random effects model was used. Publication bias was assessed by the Egger test. Results: pooled meta-analysis showed that serum α-carotene (SMD = -0.58, 95% CI (-0.83, -0.32), P < 0.001), β-carotene (SMD = -0.81, 95% CI (-1.13, -0.49), P < 0.001), and lycopene (SMD = -1.06, 95% CI (-1.74, -0.38), P < 0.001) were negatively correlated with the risk and severity of liver disease. However, no significant difference was observed between serum β-cryptoxanthin (SMD = 0.02, 95% CI (-0.41, 0.45), P = 0.92) and lutein/zeaxanthin (SMD = 0.62, 95% CI (-1.20, 2.45), P = 0.502). Dietary β-carotene intake (SMD = -0.22, 95% CI (-0.31, -0.13), P < 0.001) was negatively associated with the risk of liver disease. The Egger test showed no publication bias (P > 0.05). An intake of more than 6 mg of carotenoids on an energy-restricted diet can effectively alleviate the symptoms of NAFLD. Conclusion: lower serum concentrations of α-carotene, β-carotene, and lycopene were associated with a higher risk of liver disease. Meanwhile, dietary intake of β-carotene could reduce the incidence of liver disease. However, for malignant diseases such as liver cancer, it did not show the significant effects of carotenoid supplementation.