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john
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09/12/2008
Publishing date:
03/01/2014
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The number needed to harm we calculated as 46 (Table 1). This means that for every 46 pregnant women who consume more than two cups of coffee or six cups of tea a day, one will have a baby weighing less than 2500 grams who would not have had they not consumed this much caffeine.
Comment
This is a useful and thoughtful review, which explains, for instance, how each study deals with confounding issues like maternal age and smoking. That does not exclude unknown confounding factors, but an association between maternal caffeine intake and spontaneous abortion or low birthweight is more likely to be true than not. The review tells us that caffeine is cleared from the body much less rapidly in the second and third trimesters of pregnancy, and advises pregnant women to limit their caffeine intake to less than 150 mg a day. This seems sensible.
Coffee and colorectal cancer
Another meta-analysis comes to a somewhat tentative conclusion that high coffee consumption (perhaps four cups a day or more) reduces the risk of colorectal cancer [2]. Methodologically it is sound, and it does a nice job of discussing the subject, but it gives us relative risks for high versus low coffee consumption in people with colorectal cancer.
So the overall figure for all 17 studies with 6,192 cases was that colorectal cancer was 24% less likely in people who drink four or more cups of coffee a day - relative risk 0.76 (95% confidence interval 0.66 to 0.89).
The finding was consistent across geographically distinct areas, and in most studies except five small cohort studies with fewer than 15% of the patients studied. In three studies with 883 cases with adenomas, the relative risk was 0.57 (95% confidence interval 0.44 to 0.72).
Coffee and stroke in hypertensive non-smokers
Coffee consumption in hypertensive men in older middle-age and the risk of stroke has been examined in a long-term study in Hawaii. Coffee intake (inter alia) was measured in a large cohort of men in the late 1960s, and the incidence of stroke observed over the next 25 years in almost all the men in the study. These were men aged 55 to 68 years who were nonsmokers with hypertension (defined as systolic or diastolic blood pressure above 140 or 90 mmHg respectively).
There were 499 men, and 76 developed a stroke, 55 of which were thromboembolic. After adjusting for age, the risk of thromboembolic stroke, but not haemorrhagic stroke, was significantly related to the amount of coffee consumed (Figure 3).
For non-drinkers the five-year incidence was 2%, compared with 4% in those drinking more than three cups a day.
The risk of thromboembolic stroke was more than doubled (relative risk 2.1, 95% confidence interval 1.2 to 3.7) in those who consumed three cups of coffee a day as compared with non-drinkers.
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