Effect of Caffeine on Basal Metabolism

Abstract

Conclusions

Caffeine citrate increases the basal metabolic rate of guinea pigs. This increase is present 24 hours after feeding caffeine though not quite so marked. Lugol's solution or thyroidec tomy tends to prevent this calorigenic action.

In a recent report we called attention to the fact that when certain of the methylated purines were fed or injected into dogs morphological evidence of increased activity of the thyroid gland was obtained. 1 ,²,³,⁴ Toxic and frequently fatal doses of these substances were often required to produce such changes. These studies have been extended with especial reference to the calorigenic action of one of these purines, namely, caffeine citrate.

It has been realized for some time that caffeine possesses the ability to increase the oxygen consumption in the organism. 2 The mechanism has been vague although the adrenal glands, the skeletal muscle and the central nervous system have all been suggested as playing some part in this process. The present report has to do with the relation of the thyroid gland to this phenomenon.

Young guinea pigs weighing between 350 and 450 gm. were used. The basal metabolic rate was determined by a method previously described by us in which a closed circuit is used and direct oxygen consumption measured. A normal rate of oxygen consumption was established for each animal before the experiment was begun. These animals were placed on a basal diet of lettuce, oats and alfalfa. Basal metabolism determinations were made on alternate days for 2 weeks before the normal rate of oxygen consumption was considered established. Unless the animal showed 5 successive readings of the same rate the basal rate was not considered established. Each animal was fed 70 mg. of caffeine citrate by mouth per kilo of body weight. Apparently the method of administering the caffeine was of little importance. Determinations were made one hour later. A progressive rise in the basal metabolic rate was noticed which reached a peak at about the end of 2 weeks. At this time the increase was generally from 40%–75%. There was then a gradual decline until by the end of the fourth week the increase was more or less constant at a level of about 20%–25% increase.