Milk consumption and the risk of type 2 diabetes: A systematic review of Mendelian randomization studies

Dairy intake, plasma metabolome, and risk of type 2 diabetes in a population-based cohort

BACKGROUND

Whether dairy intake is related to type 2 diabetes (T2D) remains unclear, as does potential metabolic mechanisms for this association.

OBJECTIVES

We aimed to examine the association between high dairy intake and risk of T2D and identify plasma metabolites reflecting dairy intake.

METHODS

This prospective cohort study included 26,461 Swedish individuals recruited between 1991 and 1996 and followed up until 31 December, 2020, with available data on dairy intake at baseline and linked registers. Plasma metabolites were measured in a subsample (n = 893) using mass spectrometry. Associations of dairy intake with risk of T2D were assessed using Cox proportional hazards models, with results presented as hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

A total of 4552 new-onset incident T2D cases were documented during a median follow-up of 24.3 y. Increased risk of T2D was observed among participants consuming high nonfermented milk (>1000 g/d compared with <200 g/d; HR: 1.40; 95% CI: 1.12, 1.74) and cheese (>100 g/d compared with <20 g/d; HR: 1.23; 95% CI: 1.07, 1.41), although decreased risk of T2D was observed among those with high fermented milk (>300 g/d compared with 0 g/d; HR: 0.88; 95% CI: 0.74, 1.03), cream (>50 g/d compared with <10 g/d; HR: 0.77; 95% CI: 0.64, 0.92), and butter (>50 g/d compared with 0 g/d; HR: 0.82; 95% CI: 0.71, 0.94). Such associations were slightly attenuated after additional adjustment for BMI. In addition, we identified metabolite profiles for nonfermented milk (n = 45), fermented milk (n = 48), cheese (n = 12), cream (n = 27), and butter (n = 46); no overlap between metabolites was found.

CONCLUSIONS

In this cohort of Swedish adults, high intakes of nonfermented milk and cheese are positively associated with risk of T2D, although high intakes of fermented milk, cream, and butter are inversely associated. Metabolomics provides novel insights into understanding the metabolic pathways of these associations.

Effects of different types of milk consumption on type 2 diabetes and the mediating effect of AA: A Mendelian randomization study of East Asian populations

There is currently a lack of research examining the association between the consumption of different dairy products and type 2 diabetes (T2D) in East Asian populations. To address this gap, the present study employs Mendelian randomization to investigate the potential effects of 3 different types of milk consumption (including whole milk, semi-skim milk, and skim milk) on the risk of developing T2D. The results indicate that both whole milk and skim milk are associated with an increased risk of T2D (whole milk: odds ratio [OR] = 1.022, 95% CI: 1.001-1.044; skim milk: OR = 1.023, 95% CI: 1.007-1.039). Mediation analysis revealed that asparagine acts as a mediator between skim milk consumption and T2D, with a mediation effect of 0.003 (95% CI: 0.000 to 0.008), accounting for 14.269% of the total effect.

Dairy Intake in Relation to Prediabetes and Continuous Glycemic Outcomes: A Systematic Review and Dose-Response Meta-Analysis of Prospective Cohort Studies

Background

Modest inverse associations have been found between dairy intake, particularly yogurt, and type 2 diabetes risk. Investigating associations of dairy intake with early onset of type 2 diabetes offers opportunities for effective prevention of this condition.

Objectives

This study aims to investigate the relationships between the intake of different dairy types, prediabetes risk, and continuous glycemic outcomes.

Methods

Systematic literature searches across multiple databases were performed of studies published up to September 2023. Included were prospective cohort studies in healthy adults that examined the association between dairy intake and prediabetes risk according to diagnostic criteria, or continuous glycemic markers. A dose-response random-effects meta-analysis was used to derive incremental relative risks (RRs) for associations of total dairy, fermented dairy, milk, yogurt, cheese (all total, high-fat, and low-fat), cream, and ice cream with prediabetes risk adjusted for sociodemographic, health and cardiometabolic risk factors, and dietary characteristics.

Results

The meta-analyses encompassed 6653 prediabetes cases among 95,844 individuals (age range 45.5-65.5 y) including 6 articles describing 9 cohorts. A quadratic inverse association was observed for total dairy intake and prediabetes risk, with the lowest risk at 3.4 servings/d (RR: 0.75; 95% confidence interval: 0.60, 0.93; I 2 = 18%). Similarly, total, and high-fat cheese exhibited nonlinear inverse associations with prediabetes risk, showing the lowest risk at 2.1 servings/d (0.86; 0.78, 0.94; I 2 = 0%, and 0.90; 0.81, 0.99; I 2 = 12%), but a higher risk at intakes exceeding 4 servings/d. Ice cream intake was linearly associated with prediabetes risk (0.85; 0.73, 0.99; I 2 = 0% at the highest median intake of 0.23 servings/d). Other dairy types showed no statistically significant associations. The systematic review on dairy intake and glycemic outcomes showed considerable variabilities in design and results.

Conclusions

The findings suggest an inverse association between moderate dairy and cheese intake in preventing prediabetes. The potential for reverse causation and residual confounding highlights the need for studies with comprehensive repeated measurements.

Trial registration number

PROSPERO 2023 CRD42023431251.

Variant of the lactase LCT gene explains association between milk intake and incident type 2 diabetes

Cow's milk is frequently included in the human diet, but the relationship between milk intake and type 2 diabetes (T2D) remains controversial. Here, using data from the Hispanic Community Health Study/Study of Latinos, we show that in both sexes, higher milk intake is associated with lower risk of T2D in lactase non-persistent (LNP) individuals (determined by a variant of the lactase LCT gene, single nucleotide polymorphism rs4988235 ) but not in lactase persistent individuals. We validate this finding in the UK Biobank. Further analyses reveal that among LNP individuals, higher milk intake is associated with alterations in gut microbiota (for example, enriched Bifidobacterium and reduced Prevotella) and circulating metabolites (for example, increased indolepropionate and reduced branched-chain amino acid metabolites). Many of these metabolites are related to the identified milk-associated bacteria and partially mediate the association between milk intake and T2D in LNP individuals. Our study demonstrates a protective association between milk intake and T2D among LNP individuals and a potential involvement of gut microbiota and blood metabolites in this association.