Investigating the Effects of Vaccinium myrtillus Supplementation on Cardiometabolic Indices: A Systematic Review and Meta-Analysis.

Chronic diseases cause early death and financial strain worldwide. Cardio-metabolic health, crucial for preventing cardiovascular disease and type 2 diabetes, may benefit from bilberry's antioxidant and anti-inflammatory properties. This meta-analysis reviews studies of bilberry's impact on lipid profiles, glycemic indices, body composition, and inflammatory and oxidative factors. Inclusion criteria were randomized clinical trials assessing bilberry supplementation in adults for at least 1 week. A comprehensive review of literature was performed in PubMed, Web of Science, Scopus, and Google Scholar until July 21, 2024, without any time limitations. Mean changes and their SDs were used to calculate overall effect sizes, with the Hozo et al. method converting SEs, 95% CIs, and IQRs to SDs. A random-effects model accounted for between-study variations. Eleven RCTs, including 409 individuals, were incorporated into the present systematic review, and 8 were included in the meta-analysis. Combining five effect sizes from the five trials on long-term effects of bilberry administration compared with controls resulted in a non-significant decrease in FBG (WMD: -0.08 mmol/L, 95% CI: -0.22 to 0.07, p = 0.30). For HbA1c, the meta-analysis of three RCTs showed a marginally significant reduction (WMD: -1.63%, 95% CI: -3.36% to 0.11%, p = 0.06). The results of the meta-analysis on lipid profile showed a decreasing trend, although this reduction was not statistically significant for TC (WMD: -0.11 mmol/L, 95% CI: -0.30% to 0.08%, p = 0.27) or TG (WMD: -0.07 mmol/L, 95% CI: -0.32% to 0.19%, p = 0.62). However, a significant change in TG was reported in trials with a crossover design and RCTs with 4 weeks of intervention or less. Although HDL level did not show any significant change (WMD: -0.02 mmol/L, 95% CI: -0.10% to 0.07%, p = 0.70), the meta-analysis of five RCTs evaluating the long-term effects of bilberry supplementation revealed a significant change in LDL following bilberry supplementation (WMD: 0.07 mmol/L, 95% CI: 0.01%-0.14%, p = 0.01). Furthermore, no significant reduction was observed in SBP (WMD: -2.75 mmHg, 95% CI: -6.38% to 0.89%, p = 0.13) or DBP (WMD: -1.00 mmHg, 95% CI: -4.66% to 2.65%, p = 0.59) after bilberry supplementation. Finally, anthropometric indices including body weight (WMD: 0.04 Kg, 95% CI: -0.44% to 0.53%, p = 0.86) and inflammatory and oxidative stress markers including hs-CRP (WMD: -8.22 mg/L, 95% CI: -20.24% to 3.81%, p = 0.18), IL-6 (WMD: -7.19 pg/mL, 95% CI: -19.01% to 4.63%, p = 0.23), uric acid (WMD: -0.01 mmol/L, 95% CI: -0.03% to 0.01%, p = 0.36), and FRAP (WMD: -42.03 μmol/L, 95% CI: -100.54% to 16.48%, p = 0.16) showed no significant change after bilberry supplementation. Bilberry supplementation may have beneficial effects on HbA1c and TG, but not other cardio-metabolic indices. Therefore, long-term and high-quality trials are needed to confirm the promising effects of bilberries.