Alertness Effects of Caffeine
Caffeine is a naturally occurring compound found in over sixty species of plants.
It occurs naturally in tea and coffee and has been extensively researched. Numerous studies have looked at the effects of caffeine on mental alertness and physical performance and have shown that caffeine can have beneficial effects.
Results have shown: sustained attention during after-lunch dip (22); improved alertness and performance on a variety of tasks at night (23); improved attention, psychomotor, memory test results after strenuous exercise (24); reversed changes caused by sleep-deprivation such as decreased, fatigue (25, 26); and improved success in overcoming sleeplessness (27).
Caffeine has also been shown to significantly increase wakefulness, vigor, energy, feeling “full of go” and feeling efficient (9). Increases in cognitive performance (20, 21) and in alertness, energy, and well being (10,11) have been shown at levels of caffeine equivalent to those found in one cup of tea.
Tea vs. Coffee
In a study comparing tea and coffee, both beverages had similar effects on alertness, but tea produced more consistent levels during the day and appeared to have a more gentle reviving effect (32).
A cup of regular black or green tea has about half the caffeine as a comparable cup of regular brewed coffee. In a study in which participants drank tea and coffee continually all day in the same amounts, both beverages produced similar effects on alertness, despite tea’s lower levels of caffeine.
In addition, those people drinking tea said they got to sleep more easily, and rated their quality and actual sleep time as being better than those drinking the same number of cups of coffee (33). Together with other research conducted on caffeine and sleep (34, 35, 36, 37), these studies suggest that tea provides the potential beneficial effects of caffeine on performance during the day without disrupting sleep at night.
However, as with some other foods and beverages, pregnant women are advised to consume caffeine in moderation and to limit their daily intake of caffeine to no more than 300 mg/day as caffeine intakes above this level may be associated with low birth weights and in some cases miscarriages (40). Pregnant women are advised to discuss caffeine intake with your Health Care Professional.
| Food | Caffeine Content |
|---|---|
| Instant Coffee (1tsp/cup) | 60-80mg / 250ml cup |
| Percolated Coffee | 60-120mg / 250ml cup |
| Tea | 10-50mg / 250ml cup |
| Coca Cola | 36mg / 375ml can |
| Milk Chocolate | 20mg / bar |
| Energy Drinks (e.g. Red Bull) | 80mg / 250ml can |
Caffeine level in tea depends on various factors, including preparation method, brewing time, amount of tea leaves used, the size of the tea leaves and variations in the plant itself.