Caffeine affects cortisol levels (the stress hormone). In one study, researchers gave healthy men and women different doses of caffeine throughout the day and found that the caffeine spiked their cortisol levels1. After baseline psychological testing, the subjects were placed on a caffeine- and sugar-free diet for one week. The subjects who reported substantial improvement were then given either a capsule containing caffeine and a Kool-Aid drink sweetened with sugar, or a placebo capsule containing cellulose and a Kool-Aid drink sweetened with an artificial sweetener, for up to six days. About 50% of the test subjects became depressed during the period where they were getting caffeine and sucrose. The reason? Researchers believe it’s because caffeine worsens blood sugar control and when combined with sugar, causes blood sugar volatility that really stresses out the brain.
