Effect of folate supplementation on insulin sensitivity and type 2 diabetes: a meta-analysis of randomized controlled trials

Lind, Mads Vendelbo; Lauritzen, Lotte; Kristensen, Mette; Ross, Alastair B; Eriksen, Jane Nygaard
January 2019
American Journal of Clinical Nutrition;Jan2019, Vol. 109 Issue 1, p29
Academic Journal
Background: Various mechanisms link higher total homocysteine to higher insulin resistance (IR) and risk of type 2 diabetes (T2D). Folate supplementation is recognized as a way to lower homocysteine. However, randomized controlled trials (RCTs) show inconsistent results on IR and T2D outcomes. Objective: The aim of this study was to examine the effect of folate supplementation on IR and T2D outcomes. Design: We conducted a systematic literature search in PubMed, Web of Science, and EMBASE and prior systematic reviews and meta-analyses and identified 29 RCTs (22,250 participants) that assessed the effect of placebo-controlled folate supplementation alone or in combination with other B vitamins on fasting glucose, insulin, homeostasis model assessment for insulin resistance (HOMA-IR), glycated hemoglobin (HbA1c), or risk of T2D. The meta-analysis was conducted using both random- and fixed-effects models to calculate weighted mean differences (WMDs) or risk ratios with 95% CIs. Subgroup analyses were conducted based on intervention type (folate alone or in combination with other B vitamins), as well as analysis based on population characteristics, duration, dose, and change in homocysteine. Results: When compared with placebo, folate supplementation lowered fasting insulin (WMD: −13.47 pmol/L; 95% CI: −21.41, −5.53 pmol/L; P < 0.001) and HOMA-IR (WMD: −0.57 units; 95% CI: −0.76, −0.37 units; P < 0.0001), but no overall effects were observed for fasting glucose or HbA1c. Heterogeneity was low in all meta-analyses, and subgroup analysis showed no signs of effect modification except for change in homocysteine, with the most pronounced effects in trials with a change of >2.5 µmol/L. Changes in homocysteine after folate supplementation correlated with changes in fasting glucose (β = 0.07; 95% CI: 0.01, 0.14; P = 0.025) and HbA1c (β = 0.46; 95% CI: 0.06, 0.85; P = 0.02). Only 2 studies examined folate supplementation on risk of T2D, and they found no change in RR (pooled RR: 0.91; 95% CI: 0.80, 1.04; P = 0.16). Conclusion: Folate supplementation might be beneficial for glucose homeostasis and lowering IR, but at present there are insufficient data to conclusively determine the effect on development of T2D


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