Bright light alone delayed the internal clock by 85 minutes, and the combination of bright light and a caffeine pill delayed the clock by 105 minutes. But researchers also found that the amount of caffeine found in a double espresso can cause a 40-minute "phase delay" in our internal clock. While every roast and brew has a slightly different caffeine content, a double espresso can, in fact, have as much caffeine as one cup of coffee. The researchers also noticed that certain cells in the body, part of our "clock genes," were also altered by caffeine—it actually blocked the cell receptors that normally help people fall asleep.