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SIR,–We have shown,1 in a double-blind study, that the level of blood-glucose was significantly raised in relatively healthy males 2 hours after ingestion of 250 mg. caffeine (the equivalent of two cups of coffee). However, considerable blood-glucose-level variation was observed within the group. We here re-examine the sample in the light of the group health status.
Twenty-two junior dental students presented themselves fasting at 10 A.M. A venous blood-sample was obtained and blood-glucose measured.2,3 Immediately after the blood was drawn, each subject was asked to swallow a capsule containing 250 mg. caffeine (U.S.P.) with 5 oz. (140 ml.) of water. Blood-glucose was measured ½, 1, and 2 hours later. In addition, each student completed the Cornell Medical Index Health Questionary (C.M.I.). The total number of affirmative answers can be regarded as a crude measure of ill-health status.
Effect of caffeine upon mean blood-glucose levels (in mg. per 100 ml., on ordinate) in ten subjects with less than 8, and twelve subjects with 8 or more, ” yes ” responses on C.M.I.
Results and Discussion
The students were divided almost equally by the number of positive C.M.I. responses: ten students had C.M.I. scores of 0-7, and twelve had scores of 8-22. The means (± S.D.) for blood-glucose levels (see accompanying figure) were as follows:
It is clear that, on a mean basis, the blood-glucose values rise with time.
The statistical significance of caffeine supplementation upon blood-glucose concentration in terms of health status, considering fasting against post-caffeine levels, was as follows:
The only significantly raised blood-glucose value occurred 2 hours after caffeine supplementation in the students with the poorer C.M.I. response (8 or more ” yes ” answers), and the hyperglycemic effect of caffeine was greater than in those with fewer (0-7 ” yes ” answers) general symptoms and signs suggestive of disease.
Although the blood-glucose response to caffeine reported here is not of great magnitude, coffee-drinking habits are such that cumulative effects may occur during an average day. In addition, the peak glucose level may have occurred during a later hour. This would enhance the possibility of a cumulative response. Thus, as noted previously,1 the effect of coffee consumption on glucose homeostasis should be carefully explored, since many heavy consumers may have a predisposition to maturity-onset diabetes. Danowski4 has noted that roughly one out of four people, in the course of a lifetime, develops diabetes, or episodes of hyperglycaemia that are indistinguishable from diabetes. These observations were derived from consecutive studies of individuals from birth to death rather than from the prevalence-rate in a given community at a given time.
- Cheraskin, E., Ringsdorf, W. M., Jr., Setyaadmadja, A. T. S. H., Barrett, R. A. Lancet, 1967, i, 1299.
- Nelson, N. J. Biol. Chem. 1944, 153, 375.
- Somogyi, M. ibid. 1945, 160, 69.