Many of us enjoy a cup of coffee first thing in the morning. However, drinking coffee early in the morning can be harmful because our bodies produce high levels of cortisol at that time of day. Taking coffee during the time our bodies are producing high levels of cortisol can further increase stress hormone levels, leading to other health issues over time.Since cortisol levels are high 3 times a day, caffeine should be consumed between 10 a.m. and noon, and between 2 p.m. and 5 p.m.