Prenatal Caffeine and ADHD: Is There a Link?

Prenatal Caffeine Consumption and ADHD

Behavioral disorders, such as attention-deficit/hyperactivity disorder (ADHD), have increased over time.^[1] Risk factors, such as tobacco or alcohol use by pregnant women, have not been shown to clearly correlate with ADHD in offspring, with results varying among studies. Links between prenatal exposures and later outcomes can be evaluated through large cohort studies, using extensive clinical and socioeconomic data to control for potential confounders.

In one such analysis, the Danish National Birth Cohort study,^[1] mothers were recruited between 1996 and 2002, and data on coffee and tea consumption were obtained by maternal self-report. The outcomes of interest, determined when the study children were aged 11 years, were obtained by questionnaires completed by the children, their parents, and their teachers.

The investigators linked prenatal data on maternal caffeine consumption with behavior questionnaire outcomes for more than 47,000 children. Mothers were divided into one of four groups on the basis of their daily coffee and tea consumption:

No exposure to coffee or tea;
One half to three cups;
Four to seven cups; and
Eight or more cups.

The analyses accounted for the fact that one cup of coffee contains more caffeine than one cup of tea.

The study outcome was a standardized instrument of 25 questions, rated on a Likert scale. This instrument (although not diagnostic) grouped children into profiles that either fit or did not fit ADHD. The analysis accounted for maternal age at the time of birth, maternal body mass index, smoking during pregnancy, socioeconomic status, marital status, year of birth, and infant gender.

At 15 weeks' gestation, almost 12% of the women were consuming more than three cups of coffee daily, and 18.7% were consuming more than three cups of tea. Coffee and tea consumption were similar later in pregnancy, at 30 weeks. There was a correlation between drinking eight or more cups of coffee daily and maternal smoking, but not between high tea consumption and smoking.

A significant trend was observed for an association between increasing levels of coffee consumption and the risk for the child's score profile to fit ADHD. For example, women who consumed eight or more cups of coffee daily had an adjusted relative risk of 1.47 (95% confidence interval, 1.18-1.89) of having a child with a behavioral profile that fit ADHD. However, caffeine consumption at 30 weeks did not correlate with behavioral outcomes.

In comparison, being in the lowest socioeconomic stratum had a much stronger correlation with ADHD profile (adjusted relative risk, 2.11). The inflection point seemed to be about 750 mg of caffeine daily (eight cups or more of coffee), and a lower intake was associated with a slightly lower risk for ADHD.

The investigators concluded that high caffeine consumption at 15 weeks, but not at 30 weeks, appears to be associated with behavioral profiles in the offspring that fit ADHD. They suggest that the correlation found at 15 weeks but not at 30 weeks suggests a developmental window during which fetal brains may be more susceptible to the effects of caffeine.

Viewpoint

I love Scandinavian cohort studies. Without experimentation, they are one of the best ways we have of evaluating potential associations of environmental exposures and child outcomes. Even so, this study points out some of the limitations of such analyses.

I wouldn't interpret this study in any way as saying that pregnant women should avoid caffeine, although one could say they might want to avoid caffeine in excess. Although these analyses included a lot of information about the mothers, it's not clear how many potential childhood confounders were addressed. These threats to validity were acknowledged by the study authors, who comment that caffeine consumption often correlates with other maternal factors that may increase the risk for ADHD, including smoking, alcohol consumption, age, and education level.

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