Basically, it's unlikely that caffeine will cause insomnia unless you're more sensitive to its effects. Here are some reasons why caffeine does cause insomnia in some people:
- Caffeine naturally increases and stimulates cortisol in people (Link). "Cortisol, known as the stress hormone, helps facilitate the fight or flight mechanism designed to save us from physical threat" (Link).
- "Some experts state that cortisol can remain elevated for up to 18 hours in the blood. So it may not be the caffeine that keeps you awake at night - it may be cortisol. So even a cup of coffee at 7:00 AM can still have it's effects at 10:00 at night" (Link).
While there are positive effects of coffee such as antioxidants, there are also negative effects. For example, adrenal fatigue may occur for those who use coffee daily.
- "Shortly after the consumption of caffeine, individuals may feel a buzz from the initial effects. These include an increase in the availability of sugars and fatty acids in the bloodstream together with the stimulation of the central nervous system. However, Dr. Wilson points out that the adrenal glands have to work hard for this to happen. This can cause severe fatigue and weakness in sufferers of adrenal fatigue" (Link).
- "Your body, eventually, will start feeling chronically tired because of how constantly elevated cortisol levels have drained your body of all of its reserves" (Link).