Vitamins C, E, and ß-Carotene and Risk of Type 2 Diabetes: A Systematic Review and Meta-Analysis.

A systematic review and meta-analysis was conducted to assess the relationship between the common dietary antioxidants vitamin C, vitamin E, and ß-carotene and type 2 diabetes (T2D) and related traits. MEDLINE, Embase, and the Cochrane Library were searched for relevant publications up until May 2023. Studies were eligible if they had a cohort, case-control, or randomized controlled trial (RCT) design and examined dietary intake, supplementation, or circulating levels of these antioxidants as exposure, and insulin resistance, ß-cell function, or T2D incidence as outcomes. Summary relative risks (RR) or mean differences (MD) with 95% confidence intervals (CI) were estimated using random-effects models. The certainty of the evidence was assessed with the Grading of Recommendations, Assessment, Development and Evaluations framework. Among 6190 screened records, 25 prospective observational studies and 15 RCTs were eligible. Inverse associations were found between dietary and circulating antioxidants and T2D (observational studies). The lowest risk was seen at intakes of 70 mg/d of vitamin C (RR: 0.76; CI: 0.61, 0.95), 12 mg/d of vitamin E (RR: 0.72; CI: 0.61, 0.86), and 4 mg/d of ß-carotene (RR: 0.78; CI: 0.65, 0.94). Supplementation with vitamin E (RR: 1.01; CI: 0.93, 1.10) or ß-carotene (RR: 0.98; CI: 0.90, 1.07) did not have a protective effect on T2D (RCTs), and data on vitamin C supplementation was limited. Regarding insulin resistance, higher dietary vitamin C (RR: 0.85; CI: 0.74, 0.98) and vitamin E supplementation (MD: -0.35; CI: -0.65, -0.06) were associated with a reduced risk. The certainty of evidence was high for the associations between T2D and dietary vitamin E and ß-carotene, and low to moderate for other associations. In conclusion, moderate intakes of vitamins C, E, and ß-carotene may lower risk of T2D by reducing insulin resistance. Lack of protection with supplementation in RCTs suggests that adequate rather than high intakes may play a role in T2D prevention. This systematic review and meta-analysis was registered in PROSPERO with registration number CRD42022343482.

Antioxidant Nutrients and Risk of Latent Autoimmune Diabetes in Adults and Type 2 Diabetes: A Swedish Case-Control Study and Mendelian Randomization Analysis.

Antioxidant vitamins C and E are inversely associated with type 1 diabetes (T1D). We investigated if antioxidants are also associated with latent autoimmune diabetes in adults (LADA), with low (LADAlow) and high (LADAhigh) autoantibody levels, type 2 diabetes (T2D), and estimates of beta cell function (HOMA-B) and insulin resistance (HOMA-IR). We used Swedish case-control data with incident cases of LADA (n = 584) and T2D (n = 1989) and matched population-based controls (n = 2276). Odds ratios (OR) and 95% confidence intervals (CI) were calculated per one standard deviation higher beta-carotene, vitamin C, vitamin E, selenium, and zinc intakes. Two-sample Mendelian randomization (MR) analyses assessed causality between genetically predicted circulating antioxidants and LADA, T1D, and T2D, using summary statistics from genome-wide association studies. Among the antioxidants, vitamins C and E were inversely associated with LADAhigh (OR 0.84, CI 0.73, 0.98 and OR 0.80, CI 0.69, 0.94 respectively), but not with LADAlow or T2D. Vitamin E was also associated with higher HOMA-B and lower HOMA-IR. MR analyses estimated an OR of 0.50 (CI 0.20, 1.25) for the effect of vitamin E on T1D, but did not support causal relationships between antioxidants and either LADA or T2D. In conclusion, vitamin E may have a protective effect on autoimmune diabetes, possibly through preserved beta cell function and less insulin resistance.

Interaction between plasma phospholipid odd-chain fatty acids and GAD65 autoantibodies on the incidence of adult-onset diabetes: the EPIC-InterAct case-cohort study.

AIMS/HYPOTHESIS: Islet autoimmunity may progress to adult-onset diabetes. We investigated whether circulating odd-chain fatty acids (OCFA) 15:0 and 17:0, which are inversely associated with type 2 diabetes, interact with autoantibodies against GAD65 (GAD65Ab) on the incidence of adult-onset diabetes. METHODS: We used the European EPIC-InterAct case-cohort study including 11,124 incident adult-onset diabetes cases and a subcohort of 14,866 randomly selected individuals. Adjusted Prentice-weighted Cox regression estimated HRs and 95% CIs of diabetes in relation to 1 SD lower plasma phospholipid 15:0 and/or 17:0 concentrations or their main contributor, dairy intake, among GAD65Ab-negative and -positive individuals. Interactions between tertiles of OCFA and GAD65Ab status were estimated by proportion attributable to interaction (AP). RESULTS: Low concentrations of OCFA, particularly 17:0, were associated with a higher incidence of adult-onset diabetes in both GAD65Ab-negative (HR 1.55 [95% CI 1.48, 1.64]) and GAD65Ab-positive (HR 1.69 [95% CI 1.34, 2.13]) individuals. The combination of low 17:0 and high GAD65Ab positivity vs high 17:0 and GAD65Ab negativity conferred an HR of 7.51 (95% CI 4.83, 11.69), with evidence of additive interaction (AP 0.25 [95% CI 0.05, 0.45]). Low dairy intake was not associated with diabetes incidence in either GAD65Ab-negative (HR 0.98 [95% CI 0.94, 1.02]) or GAD65Ab-positive individuals (HR 0.97 [95% CI 0.79, 1.18]). CONCLUSIONS/INTERPRETATION: Low plasma phospholipid 17:0 concentrations may promote the progression from GAD65Ab positivity to adult-onset diabetes.

Maternal smoking during pregnancy and type 1 diabetes in the offspring: a nationwide register-based study with family-based designs.

BACKGROUND: Maternal smoking during pregnancy was reported to be associated with a reduced risk of type 1 diabetes in the offspring. We investigated whether this association is consistent with a causal interpretation by accounting for familial (shared genetic and environmental) factors using family-based, quasi-experimental designs. METHODS: We included 2,995,321 children born in Sweden between 1983 and 2014 and followed them for a diagnosis of type 1 diabetes until 2020 through the National Patient, Diabetes and Prescribed Drug Registers. Apart from conducting a traditional cohort study, we performed a nested case-control study (quasi-experiment) comparing children with type 1 diabetes to their age-matched siblings (or cousins). Information on maternal smoking during pregnancy was retrieved from the Swedish Medical Birth Register. Multivariable adjusted Cox proportional hazards regression and conditional logistic regression were used. RESULTS: A total of 18,617 children developed type 1 diabetes, with a median age at diagnosis of 9.4 years. The sibling and cousin comparison design included 14,284 and 7988 of these children, respectively. Maternal smoking during pregnancy was associated with a 22% lower risk of offspring type 1 diabetes in the full cohort (hazard ratio 0.78, 95% confidence interval [CI] 0.75-0.82). The corresponding odds ratio was 0.78 (95% CI 0.69-0.88) in the sibling and 0.72 (95% CI 0.66-0.79) in the cousin comparison analysis. CONCLUSIONS: This nationwide, family-based study provides support for a protective effect of maternal smoking on offspring type 1 diabetes. Mechanistic studies are needed to elucidate the underlying pathways behind this link.

Birthweight, BMI in adulthood and latent autoimmune diabetes in adults: a Mendelian randomisation study.

AIMS/HYPOTHESIS: Observational studies have found an increased risk of latent autoimmune diabetes in adults (LADA) associated with low birthweight and adult overweight/obese status. We aimed to investigate whether these associations are causal, using a two-sample Mendelian randomisation (MR) design. In addition, we compared results for LADA and type 2 diabetes. METHODS: We identified 43 SNPs acting through the fetal genome as instrumental variables (IVs) for own birthweight from a genome-wide association study (GWAS) of the Early Growth Genetics Consortium (EGG) and the UK Biobank. We identified 820 SNPs as IVs for adult BMI from a GWAS of the UK Biobank and the Genetic Investigation of ANthropometric Traits consortium (GIANT). Summary statistics for the associations between IVs and LADA were extracted from the only GWAS involving 2634 cases and 5947 population controls. We used the inverse-variance weighted (IVW) estimator as our primary analysis, supplemented by a series of sensitivity analyses. RESULTS: Genetically determined own birthweight was inversely associated with LADA (OR per SD [~500 g] decrease in birthweight 1.68 [95% CI 1.01, 2.82]). In contrast, genetically predicted BMI in adulthood was positively associated with LADA (OR per SD [~4.8 kg/m2] increase in BMI 1.40 [95% CI 1.14, 1.71]). Robust results were obtained in a range of sensitivity analyses using other MR estimators or excluding some IVs. With respect to type 2 diabetes, the association with birthweight was not stronger than in LADA while the association with adult BMI was stronger than in LADA. CONCLUSIONS/ INTERPRETATION: This study provides genetic support for a causal link between low birthweight, adult overweight/obese status and LADA.

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

BACKGROUND: 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. METHODS: 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. FINDINGS: 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. INTERPRETATION: 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. FUNDING: Swedish Research Council, Swedish Research Council for Health, Working Life and Welfare (FORTE), Novo Nordisk Foundation, and Swedish Diabetes Foundation.

Combined lifestyle factors and the risk of LADA and type 2 diabetes - Results from a Swedish population-based case-control study.

AIMS: We investigated the risk of latent autoimmune diabetes in adults (LADA) and type 2 diabetes in relation to a healthy lifestyle, the proportion of patients attributable to an unhealthy lifestyle, and the influence of family history of diabetes (FHD) and genetic susceptibility. METHODS: The population-based study included incident LADA (n = 571), type 2 diabetes (n = 1962), and matched controls (n = 2217). A healthy lifestyle was defined by BMI < 25 kg/m2, moderate-to-high physical activity, a healthy diet, no smoking, and moderate alcohol consumption. We estimated odds ratios (OR) with 95% confidence intervals (CIs) adjusted for age, sex, education, and FHD. RESULTS: Compared to a poor/moderate lifestyle, a healthy lifestyle was associated with a reduced risk of LADA (OR 0.51, CI 0.34-0.77) and type 2 diabetes (OR 0.09, CI 0.05-0.15). A healthy lifestyle conferred a reduced risk irrespective of FHD and high-risk HLA genotypes. Having a BMI < 25 kg/m2 conferred the largest risk reduction for both LADA (OR 0.54, CI 0.43-0.66) and type 2 diabetes (OR 0.12, CI 0.10-0.15) out of the individual items. CONCLUSION: People with a healthy lifestyle, especially a healthy body weight, have a reduced risk of LADA including those with genetic susceptibility to diabetes.

Consumption of red meat, genetic susceptibility, and risk of LADA and type 2 diabetes.

PURPOSE: Red meat consumption is positively associated with type 1 (T1D) and type 2 (T2D) diabetes. We investigated if red meat consumption increases the risk of latent autoimmune diabetes in adults (LADA) and T2D, and potential interaction with family history of diabetes (FHD), HLA and TCF7L2 genotypes. METHODS: Analyses were based on Swedish case-control data comprising incident cases of LADA (n = 465) and T2D (n = 1528) with matched, population-based controls (n = 1789; n = 1553 in genetic analyses). Multivariable-adjusted ORs in relation to self-reported processed and unprocessed red meat intake were estimated by conditional logistic regression models. Attributable proportion (AP) due to interaction was used to assess departure from additivity of effects. RESULTS: Consumption of processed red meat was associated with increased risk of LADA (per one servings/day OR 1.27, 95% CI 1.07-1.52), whereas no association was observed for unprocessed red meat. For T2D, there was no association with red meat intake once BMI was taken into account. The combination of high (> 0.3 servings/day vs. less) processed red meat intake and high-risk HLA-DQB1 and -DRB1 genotypes yielded OR 8.05 (95% CI 4.86-13.34) for LADA, with indications of significant interaction (AP 0.53, 95% CI 0.32-0.73). Results were similar for the combination of FHD-T1D and processed red meat. No interaction between processed red meat intake and FHD-T2D or risk variants of TCF7L2 was seen in relation to LADA or T2D. CONCLUSION: Consumption of processed but not unprocessed red meat may increase the risk of LADA, especially in individuals with FHD-T1D or high-risk HLA genotypes.

Interaction Between GAD65 Antibodies and Dietary Fish Intake or Plasma Phospholipid n-3 Polyunsaturated Fatty Acids on Incident Adult-Onset Diabetes: The EPIC-InterAct Study.

OBJECTIVE: Islet autoimmunity is associated with diabetes incidence. We investigated whether there was an interaction between dietary fish intake or plasma phospholipid n-3 polyunsaturated fatty acid (PUFA) concentration with the 65-kDa isoform of GAD (GAD65) antibody positivity on the risk of developing adult-onset diabetes. RESEARCH DESIGN AND METHODS: We used prospective data on 11,247 incident cases of adult-onset diabetes and 14,288 noncases from the EPIC-InterAct case-cohort study conducted in eight European countries. Baseline plasma samples were analyzed for GAD65 antibodies and phospholipid n-3 PUFAs. Adjusted hazard ratios (HRs) for incident diabetes in relation to GAD65 antibody status and tertiles of plasma phospholipid n-3 PUFA or fish intake were estimated using Prentice-weighted Cox regression. Additive (proportion attributable to interaction [AP]) and multiplicative interactions between GAD65 antibody positivity (≥65 units/mL) and low fish/n-3 PUFA were assessed. RESULTS: The hazard of diabetes in antibody-positive individuals with low intake of total and fatty fish, respectively, was significantly elevated (HR 2.52 [95% CI 1.76-3.63] and 2.48 [1.79-3.45]) compared with people who were GAD65 antibody negative and had high fish intake, with evidence of additive (AP 0.44 [95% CI 0.16-0.72] and 0.48 [0.24-0.72]) and multiplicative (P = 0.0465 and 0.0103) interactions. Individuals with high GAD65 antibody levels (≥167.5 units/mL) and low total plasma phospholipid n-3 PUFAs had a more than fourfold higher hazard of diabetes (HR 4.26 [2.70-6.72]) and an AP of 0.46 (0.12-0.80) compared with antibody-negative individuals with high n-3 PUFAs. CONCLUSIONS: High fish intake or relative plasma phospholipid n-3 PUFA concentrations may partially counteract the increased diabetes risk conferred by GAD65 antibody positivity.

Genotypes of HLA, TCF7L2, and FTO as potential modifiers of the association between sweetened beverage consumption and risk of LADA and type 2 diabetes.

PURPOSE: Sweetened beverage consumption is associated with type 2 diabetes (T2D) and LADA. We investigated to what extent this association is mediated by BMI and whether it is modified by genotypes of HLA, TCF7L2 rs7903146, or FTO rs9939609. METHODS: Swedish case-control data including incident cases of LADA (n = 386) and T2D (n = 1253) with matched population-based controls (n = 1545) was used. We estimated adjusted ORs of diabetes (95% CI) in relation to sweetened beverage intake (per daily 200 mL serving) and genotypes. The impact of BMI was estimated using causal mediation methodology. Associations with HOMA-IR and HOMA-B were explored through linear regression. RESULTS: Sweetened beverage intake was associated with increased risk of LADA (OR 1.15, 95% CI 1.03-1.29) and T2D (OR 1.21, 1.11-1.32). BMI was estimated to mediate 17% (LADA) and 56% (T2D) of the total risk. LADA was associated with risk variants of HLA (3.44, 2.63-4.50) and TCF7L2 (1.27, 1.00-1.61) but not FTO. Only among non-carriers of high-risk HLA genotypes was sweetened beverage intake associated with risk of LADA (OR 1.32, 1.06-1.56) and HOMA-IR (beta = 0.162, p = 0.0047). T2D was associated with TCF7L2 and FTO but not HLA, and the risk conferred by sweetened beverages appeared modified by FTO (OR 1.45, 95% CI 1.21-1.73 in non-carriers). CONCLUSIONS: Our findings suggest that sweetened beverages are associated with LADA and T2D partly through mediation by excess weight, but possibly also through other mechanisms including adverse effects on insulin sensitivity. These effects seem more pronounced in individuals without genetic susceptibility.

Interaction Between Overweight and Genotypes of HLA, TCF7L2, and FTO in Relation to the Risk of Latent Autoimmune Diabetes in Adults and Type 2 Diabetes.

OBJECTIVE: We investigated potential interactions between body mass index (BMI) and genotypes of human leukocyte antigen (HLA), TCF7L2-rs7903146, and FTO-rs9939609 in relation to the risk of latent autoimmune diabetes in adults (LADA) and type 2 diabetes. METHODS: We pooled data from two population-based studies: (i) a Swedish study with incident cases of LADA [positive for glutamic acid decarboxylase autoantibodies (GADA); n = 394) and type 2 diabetes (negative for GADA; n = 1290) and matched controls without diabetes (n = 2656) and (ii) a prospective Norwegian study that included incident cases of LADA (n = 131) and type 2 diabetes (n = 1901) and 886,120 person-years of follow-up. Analyses were adjusted for age, sex, physical activity, and smoking. Interaction between overweight (BMI ≥ 25 kg/m2) and HLA/TCF7L2/FTO high-risk genotypes was assessed by attributable proportion due to interaction (AP). RESULTS: The combination of overweight and high-risk genotypes of HLA, TCF7L2, and FTO was associated with pooled relative risk (RRpooled) of 7.59 (95% CI, 5.27 to 10.93), 2.65 (95% CI, 1.97 to 3.56), and 2.21 (95% CI, 1.60 to 3.07), respectively, for LADA, compared with normal-weight individuals with low/intermediate genetic risk. There was a significant interaction between overweight and HLA (AP, 0.29; 95% CI, 0.10 to 0.47), TCF7L2 (AP, 0.31; 95% CI, 0.09 to 0.52), and FTO (AP, 0.38; 95% CI, 0.15 to 0.61). The highest risk of LADA was seen in overweight individuals homozygous for the DR4 genotype [RR, 26.76 (95% CI, 15.42 to 46.43); AP, 0.58 (95% CI, 0.32 to 0.83) (Swedish data)]. Overweight and TCF7L2 also significantly interacted in relation to type 2 diabetes (AP, 0.26; 95% CI, 0.19 to 0.33), but no interaction was observed with high-risk genotypes of HLA or FTO. CONCLUSIONS: Overweight interacts with HLA high-risk genotypes but also with genes associated with type 2 diabetes in the promotion of LADA.

Sweetened beverage intake and risk of latent autoimmune diabetes in adults (LADA) and type 2 diabetes.

OBJECTIVE: Sweetened beverage intake is associated with increased risk of type 2 diabetes, but its association with autoimmune diabetes is unclear. We aimed to investigate sweetened beverage intake and risk of latent autoimmune diabetes in adults (LADA); autoimmune diabetes with features of type 2 diabetes. DESIGN/METHODS: Data from a Swedish population-based study was used, including incident cases of LADA (n = 357) and type 2 diabetes (n = 1136) and randomly selected controls (n = 1371). Diabetes classification was based on onset age (≥35), glutamic acid decarboxylase autoantibodies (GADA) and C-peptide. Sweetened beverage intake information was derived from a validated food frequency questionnaire. ORs adjusted for age, sex, family history of diabetes, education, lifestyle, diet, energy intake and BMI were estimated using logistic regression. RESULTS: Daily intake of >2 servings of sweetened beverages (consumed by 6% of participants) was associated with increased risk of LADA (OR: 1.99, 95% CI: 1.11-3.56), and for each 200 mL daily serving, OR was 1.15 (95% CI: 1.02-1.29). Findings were similar for sugar-sweetened (OR: 1.18, 95% CI: 1.00-1.39) and artificially sweetened beverages (OR: 1.12, 95% CI: 0.95-1.32). Similarly, each daily serving increment in total sweetened beverage conferred 20% higher type 2 diabetes risk (95% CI: 1.07-1.34). In type 2 diabetes patients, high consumers displayed higher HOMA-IR levels (4.5 vs 3.5, P = 0.0002), but lower HOMA-B levels (55 vs 70, P = 0.0378) than non-consumers. Similar tendencies were seen in LADA. CONCLUSIONS: High intake of sweetened beverages was associated with increased risk of LADA. The observed relationship resembled that with type 2 diabetes, suggesting common pathways possibly involving insulin resistance.