First trimester coffee and tea intake and risk of gestational diabetes mellitus: a study within a national birth cohort

Objective Coffee and tea consumption is associated with a decreased type 2 diabetes risk in non-pregnant adults. We examined the relation between first trimester coffee and tea consumption and gestational diabetes mellitus (GDM) risk. Design Population-based cohort study. Setting Denmark 1996-2002. Population Non-diabetic women with singleton pregnancies in the Danish National Birth Cohort (n = 71 239). Methods Estimated adjusted relative risks (RR) and 95% confidence intervals (95% CI) for the association between first trimester coffee and tea or estimated total caffeine and GDM. Main outcome measures GDM ascertained from the National Hospital Discharge Register or maternal interview. Results Coffee or tea intake was reported in 81.2% (n = 57 882) and 1.3% (n = 912) of pregnancies were complicated by GDM. Among non-consumers, 1.5% of pregnancies were complicated by GDM. Among coffee drinkers, GDM was highest among women who drank = 8 cups/day (1.8%) with no significant difference across intake levels (P = 0.10). Among tea drinkers, there was no difference in GDM across intake levels (1.2%; P = 0.98). After adjustment for age, socio-occupational status, parity, pre-pregnancy body mass index, smoking, and cola, there was suggestion of a protective, but non-significant association with increasing coffee (RR = 8 versus 0 cups/day = 0.89 [95% CI 0.64-1.25]) and tea (RR = 8 versus 0 cups/day = 0.77 [95% CI 0.55-1.08]). Results were similar by smoking status, except a non-significant 1.45-fold increased risk with = 8 coffee cups/day for non-smokers. There was a non-significant reduced GDM risk with increasing total caffeine. Conclusions Our results suggest that moderate first trimester coffee and tea intake were not associated with GDM increased risk and possibly may have a protective effect.