In a study reported in the BMJ and accompanied with an Editorial the effect of caffeine intake during pregnancy is discussed
There are two variables which are important for the mother.
The metabolism of caffeine depends on genetic and environmental factors. Caffeine is metabolised in the liver primarily by CYP1A2 and NAT2, and people can be classified as slow or fast metabolisers. The foetuses of women who are slow metabolisers will be exposed to more caffeine than the foetuses of fast metabolisers with an equivalent caffeine intake.
Caffeine is rapidly absorbed and crosses the placenta freely. After ingestion of 200 mg caffeine, intervillous blood flow in the placentahas been found to be reduced by 25%. Cytochrome P450 1A2, the principal enzyme involved in caffeine metabolism, is absent in the placenta and the foetus. The amount of caffeine and metabolites available to the foetoplacental unit therefore depends on the maternal caffeine metabolism, which shows marked variation between individuals, Varia¬tions in caffeine metabolic activity have been found to be more closely associated with foetal growth restriction than have blood caffeine concentrations.
Coffee and tea contain a variety of chemical com¬pounds, but most of the health concerns relate to caffeine. One cup of coffee contains about 100 mg of caffeine and a cup of tea about half of this amount; the exact amount varies according to cup size, brewing methods, and brands of coffee or tea. Caffeine is also present in cola, chocolate, cocoa, and some drugs. Most of the caf¬feine that adults consume comes from coffee, but in the present study 60% of the caffeine that pregnant women consumed came from tea.
Drinking coffee and tea correlate with other life¬style factors like smoking, work load, and perhaps also dietary habits
The results show that faster metabolisers have a higher risk than women with a slower clearance rate who have the same caffeine intake. This indicates that it is not caffeine but one of its metabo¬lites that causes harm—this notion is supported by another study based on biomarkers for caffeine exposure. Slow metabolisers with a high intake of caffeine may not be comparable with fast metabolisers with a similar intake.
In the linked cohort study, the CARE Study Group reports that consuming caffeine during pregnancy is associated with an increased risk of foetal growth restric¬tion. For 100-199 mg caffeine a day the odds ratio was 1.2 . for 200-299 mg a day 1.4. and for over 300 mg a day l.5..
What advice should we give to women who are or intend to become pregnant. The authors suggest that every effort should be made to stop pregnant women consuming caf¬feine or to reduce intake greatly,
The accompanying editorial does not totally agree with the advise about how much to reduce caffeine intake , but . the general drift is that caffeine intake is to be watched.
CARE study Group Maternal caffeine intake during pregnancy and risk of foetal growth restriction: a large prospective observational study BMJ vol 337, pp1334-8
Olsen and Bech 2008 Caffeine intake during pregnancy should be minimised but not replaced with unhealthy alternatives BMJ volume 337, pp 1305-1306
- Martin Eastwood