Gender Differences in the Metabolic Responses to Caffeine

This chapter will not review fundamental aspects of caffeine’s effects on metabolism during exercise (there are many reviews that address this ^{1 , 2 , 3 , 4} ), but will focus on the potential for men and women to have different responses to caffeine ingestion. Caffeine is clearly a potent ergogenic drug (Figure 13.1), but as in most areas of metabolic and exercise physiology the studies almost exclusively have used male subjects. This is highlighted by a recent text by Spiller ⁵ on caffeine. There is a very wide range of topics addressed in the text (including the metabolism of methylxanthines, Figure 13.1 The impact of caffeine ingestion on endurance time. Data from studies in which endurance was measured using protocols in which the power output was not varied. The number beside the data point indicates the reference number. The horizontal solid line indicates where a data point would be placed if there was no change from the placebo condition. Filled symbols represent data that was significantly different from placebo and an open symbol represents a nonsignificant finding. The square represents the one study that presented for women.<xref ref-type="bibr" rid="ref13_7"> ⁷ </xref> In those cases where the same study Is presented more than once this is because different caffeine doses,<xref ref-type="bibr" rid="ref13_51"> ⁵¹ </xref> ^, <xref ref-type="bibr" rid="ref13_69"> ⁶⁹ </xref> ^, <xref ref-type="bibr" rid="ref13_83"> ⁸³ </xref> methylxanthines,<xref ref-type="bibr" rid="ref13_54"> ⁵⁴ </xref> days of withdrawl,<xref ref-type="bibr" rid="ref13_53"> ⁵³ </xref> exercise modes,<xref ref-type="bibr" rid="ref13_11"> ¹¹ </xref> or genders<xref ref-type="bibr" rid="ref13_7"> ⁷ </xref> were studied https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351072229/ff5317ee-ad83-4ecd-b20f-191d8c294c2d/content/fig13_1.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> 302thines, caffeine as a ergogenic agent, caffeine’s effects on metabolism), but women, estrogen, progesterone etc. are not considered except in the brief final chapter on reproductive function. This is unfortunate both for practical reasons and because caffeine is potentially a very valuable research tool to explore a wide range of possible gender differences. Caffeine and other methylxanthines are metabolized within the hepatic P450 system. Caffeine has been suggested as a probe to study the integrity of this system and thus it also could be used to examine potential male/female differences in the metabolic pathway.