The article by Hinkle et al. examined the relationship between first-trimester coffee and tea consumption and risk of gestational diabetes mellitus (GDM) in an epidemiological study of a retrospective cohort. These investigators found that moderate first-trimester coffee and tea consumption was not associated with an increased risk of GDM. Important merits of this work are the use of a large well-characterised population-based cohort, and reasonable characterisation of exposure and outcome, given the self-reported nature of the data.

The pathogenesis of GDM is influenced by an overly robust increase in insulin resistance beyond the physiological increase that occurs in non-diabetic human pregnancy. The concept that caffeine may influence this adaptation is intriguing, and is grounded in data from non-pregnant populations.

Based on the nature of the collection of the primary exposure, it is not possible to discern the direct contribution of specific components of coffee and tea (e.g. caffeine). In humans, caffeine is not consumed in isolation, but rather in the context of foods or beverages that contain a wide and diverse range of micronutrients, macronutrients, preservatives, and additives. To discern the ‘pure’ effect of caffeine on insulin resistance, glycaemia, or other related phenotypes, it is perhaps more suitable to consider animal model systems. Although not significant statistically, the possibility that the relationship between coffee and tea consumption depends upon smoking status deserves future study, in both epidemiological studies and mechanistic studies.

Given the design of the study and the available data in the Danish National Birth Cohort, the relationship between coffee and tea consumption and glucose tolerance (e.g. plasma glucose concentration after a fixed glucose load) remains unexplored. Further exploration of the underlying biology of the relationship between caffeine intake during pregnancy and inflammation, insulin resistance, and the adipocytokine milieu may give insights into processes such as normal and abnormal fetal growth, and gestational hypertension. From an epidemiological perspective, an opportunity for future exploration is the interrogation of a relationship between coffee and tea consumption with gestational weight gain, from pre-pregnancy through to the early third trimester, when GDM is customarily diagnosed.

In terms of clinical and public health implications, the results of the article by Hinkle et al. are reassuring with respect to the influence of moderate coffee and tea consumption on risk of gestational diabetes. Based on this work, this reassurance can be reflected in the counselling of pregnant women.

Disclosure of interests

The author has no conflicts of interest to disclose.