“If your liver is very hypothyroid and slow to metabolize things, you might have to stop your coffee in the early afternoon because it will keep circulating the caffeine. But when your liver is able to store glycogen, coffee right up to bedtime can improve the depths of your sleep because one of the anti-stress things it does is to act as an aromatase inhibitor and since estrogen turns on serotonin and histamine and other stress hormones, caffeine—by taking down estrogen—will let your deep sleep come on.”