Dietary factors and risk of islet autoimmunity and type 1 diabetes: a systematic review and meta-analysis

Numerous dietary components have been linked to the development of islet autoimmunity (IA) and type 1 diabetes (T1D); however, no associations are firmly established. This systematic review and meta-analysis aimed to synthesize current knowledge on diet and incidence of IA and T1D.Literature search was performed in Medline, Embase, and Cochrane Library, from inception until October 2020. Eligible studies had IA or T1D as outcome; any dietary exposure; case-control, cohort, or randomized controlled trial design; and hazard, risk, or odds ratios as measures of association. Summary relative risks (RR) and 95% confidence intervals (CI) were estimated with random-effects models. Certainty of evidence was assessed with GRADE. PROSPERO registration number: CRD42020212505.Among 5935 identified records, 96 were eligible, and pooled estimates could be produced for 26 dietary factors. Evidence with moderate/high certainty indicated lower risk of T1D in relation to longer (≥6-12 vs <6-12 months, RR: 0⋅39, CI: 0⋅26-0⋅58, I2=43%) and exclusive (≥2-3 vs <2-3 months, RR: 0⋅68, CI: 0⋅58-0⋅80, I2=0%) breastfeeding, later introduction to gluten (3-6 vs <3-5 months, RR: 0⋅36, CI: 0⋅17-0⋅75, I2=0%), cow's milk (≥2-3 vs <2-3 months, RR: 0⋅69, CI: 0⋅59-0⋅81, I2=0%), and fruit (4-6 vs <4-5 months, RR: 0⋅47, CI: 0⋅25-0⋅86, I2=0%). Higher childhood intake of cow's milk was associated with increased risk of both IA (per 2-3 portions/day, RR: 1⋅25, CI: 1⋅06-1⋅47, I2=0%) and T1D (≥2-3 vs <2-3 glasses/day, RR: 1⋅81, CI: 1⋅12-2⋅91, I2=31%). For the remaining dietary factors investigated, there was no association, or the evidence was of low certainty.This study suggests that breastfeeding and late introduction of gluten, fruit, and cow's milk may reduce the risk of T1D, whereas high childhood cow's milk intake may increase it.Swedish Research Council, Swedish Research Council for Health, Working Life and Welfare (FORTE), Novo Nordisk Foundation, and Swedish Diabetes Foundation.