Caffeine is a natural chemical with stimulant effects. It is found in products like coffee, tea, cola, cocoa and so many more. Coffee for instance, is rated the highest consumed stimulant in the world and more than 90% of Americans consume caffeine products every day. When you consume caffeine, it stimulates the central nervous system, heart and the centers that control your blood pressure.
The most common uses of caffeine are for mental alertness, headaches, migraines, athletic performance and memory. However, the more caffeine you consume, the higher your tolerance to it becomes which can lead to consuming more than the "recommended" amount.
Shi J. found that tolerance depends on the amount of caffeine consumed and the times of consumption and elimination. Their model suggests that it can take up to 20 hours for the effects of caffeine to wear off.
The U.S. Food and Drug Administration recommends no more than 400 milligrams (4 cups of coffee) per day. Pregnant women should not consume more than 200 milligrams of caffeine according to the American College of Obstetricians and Gynecologists. Children under the age of 12 should not consume any foods or beverages with caffeine.
Caffeine can become harmful to ones body when used for a long time or doses over 400mg and can cause disruptions in sleep.
But it isn't all bad news, the ability of caffeine to enhance physical performance was identified in the early 20th century. This has led to not only scholarly but military interest in the role of nutrition of physical performance. The Military Nutrition Division of the US Army Research Institute of Environmental Medicine found positive nutritional components in caffeine that stand out as being most positive.
Caffeine is placed as an unusual substance to enhance performance that can have positive effects, but one side effect is sleep deprivation which can lead to performance deficits.
Like mentioned above, caffeine can be effective for migraines, headaches and mental alertness. It can become harmful once you reach the recommended daily limit. Negative side effects include irregular heart beats and even death.
When you should avoid caffeine:
While pregnant or breast-feeding
Children under 12
High blood pressure
The most common relationship between caffeine consumption and sleep quality is that it can cause your melatonin (hormone that promotes sleep) levels to drop since both are metabolized in the liver.
When you consume caffeine daily, your body gets into an on-going cycle of caffeine enhancement and deficit. The figure below shows the cycle benefits and disbenefits of consuming caffeine:
If your caffeine consumption is not wisely regulated, it can cause you to fall into this cycle. It suggests that performance deficits caused by sleep deprivation linked to caffeine can be reversed by consumption during the following day. However, sleep deprivation will still ensue followed by performance deficits the day after.
Consumption by day causes a reduction in 6-sulfatoxymelatonin (main metabolite of melatonin) at night which is one of the reasons why sleep is interrupted. Intake later in the day can also have negative effects at night when you are trying to sleep.
Although developing a caffeine tolerance by consuming it regularly overtime may lower its disruptive effects, if you have trouble sleeping, you should consider limiting caffeine intake later in the day and at night.
Shi J, Benowitz N, Denaro C, Sheiner L. Population pharmacokinetic modeling pharmacodynamic modeling of caffeine-tolerance to pressor effects. Paper presented at: Clinical Pharmacology & Therapeutics Ninety-third Annual Meeting; March 18–20; 1992; Orlando, FL, USA. [Google Scholar]