If you've ever felt compelled to start your day with a strong cup of coffee, you may be surprised to learn that caffeine can cause fatigue. Although it gets more attention for its stimulant properties, caffeine can actually make you more tired in the long run in a couple of ways, and it has everything to do with the process that goes on inside your body when you drink it.
Fight or Flight
Caffeine triggers a "fight or flight" response in your body. When it hits your bloodstream, which can be as little as 15 minutes after your first sip, it goes directly to your brain and binds with adenosine receptors. The "lost" adenosine left circulating panics your heart and adrenal glands, which release chemicals that tell your body to get ready for either intense physical combat or expedient escape. In response, your blood supply is diverted to your limbs, your heart pumps faster and more blood with each stroke to deliver more oxygen to your muscles, and your veins constrict to speed the blood along faster. What you perceive as increased energy is actually your body on high alert.
Stress
If you've ever been in a minor accident -- major enough to be momentarily terrifying, but minor enough that you weren't hurt -- you may have noticed feelings of exhaustion once you calmed down. The accident triggered a fight or flight response similar to caffeine, only bigger. But even your body's response to caffeine uses a tremendous amount of internal resources, and once the initial rush is over, you begin to feel the depletion. Within a few hours, you will feel downright tired.
Re-Dose
To combat the eventual crash after a caffeine dose, many people turn to more caffeine. This only perpetuates the cycle. If you allow the dose-crash-dose cycle to continue throughout the day, you end up with too much caffeine left in your system when it's time to go to bed. You end up laying awake, reducing the amount of time you have to sleep. If you do get to sleep, it is likely a light sleep that won't provide the restorative qualities of deep sleep. Either way, instead of waking up refreshed, you wake up groggy and exhausted, reaching for the caffeine. And the cycle continues.
Use
Caffeine is safe in moderate amounts, but the tolerable dose depends upon the person. Some people are very sensitive to caffeine and can't handle it at all, while others can drink it before bed with little difficulty. Three cups of coffee, about 24 oz. total, is considered a moderate daily amount and is not likely to do harm. Instead of pouring another cup of coffee in the afternoon, try picking up your energy with some fresh fruit or vegetable juice -- these contain carbohydrates that affect your blood sugar enough to give you a boost, but they won't stick around until bedtime.
