The time it takes for the body to eliminate one half of a caffeine dose is normally between 3 to 12 hours. It is called the half-life of caffeine. Several factors can shorten or lengthen the half life of caffeine. Smoking, medications and diseases are some factors. Pregnant women have higher caffeine half-life, 18 to 20 hours - pretty much longer for the fetus since its organs are not yet fully formed to be able to eliminate caffeine easily. About 99% of the elimination process takes place in the liver.
The effects of caffeine can begin as soon as you swallow your caffeinated beverage or food. It easily enters the bloodstream through the stomach and the intestines. Noticeable effects can be experienced 15 minutes after ingesting and peaking at around 30 - 60 minutes.
If you regularly drink a cup of coffee or tea in the morning and another in the evening, you can expect to have caffeine in your blood every hour of the day. The effect of caffeine in your body will be active 24/7. Stress hormones are released by the adrenal glands because caffeine fools your body into thinking that you are in a stressful situation. It follows that your body is in stress mode 24/7. We cannot avoid it but we normally encounter stressful situations in our daily lives and ingesting caffeine heightens the stress effects.
We know that coffee and tea are rich in antioxidants and having these in our body gives us better protection against diseases. The irony is that coffee and tea also contain caffeine which may not be good if you take more than 250 mg (approximately 10 cups of green tea or 3 cups of coffee). Nausea, dizziness, headaches and irregular heart beats are some symptoms of taking too much caffeine.
Decaffeinated coffee or tea may be helpful although they are not totally caffeine free. At least only a little caffeine is left and you can drink more without having the symptoms of caffeine overdose and getting more benefits from antioxidants that these beverages contain. See the benefits you get from this decaffeinated herbal green tea .
An alternative to drinking decaffeinated tea is decaffeinating it yourself. See my earlier post: Decaffeinated Tea.