Effects of caffeine vary with quantity and gender

January, 2011

Two recent studies suggest that caffeine is most effective in boosting your energy and alertness in small doses, and more effective for males.

A study involving 80 college students (34 men and 46 women) between the ages of 18 and 40, has found that those given a caffeinated energy drink reported feeling more stimulated and less tired than those given a decaffeinated soda or no drink. However, although reaction times were faster for those consuming caffeine than those given a placebo drink or no drink, reaction times slowed for increasing doses of caffeine, suggesting that smaller amounts of caffeine are more effective.

The three caffeine groups were given caffeine levels of either 1.8 ml/kg, 3.6 ml/kg or 5.4 ml/kg. The computerized "go/no-go" test which tested their reaction times was given half an hour after consuming the drinks.

In another study, 52 children aged 12-17 drank flattened Sprite containing caffeine at four concentrations: 0, 50 mg, 100 mg or 200 mg. Changes in blood pressure and heart rate were then checked every 10 minutes for one hour, at which point they were given a questionnaire and an opportunity to eat all they wanted of certain types of junk food.

Interestingly, there were significant gender differences, with boys drinking high-caffeine Sprite showing greater increases in diastolic blood pressure (the lower number) than boys drinking the low-caffeine Sprite, but girls being unaffected. Boys were also more inclined to report consuming caffeine for energy or “the rush”, than girls were.

Those participants who ingested the most caffeine also ate more high-sugar snack foods in the laboratory, and reported higher protein and fat consumption outside the lab.

Reference: 

[2047] Howard, M. A., & Marczinski C. A.
(2010).  Acute Effects of a Glucose Energy Drink on Behavioral Control.
Experimental and Clinical Psychopharmacology. 18(6), 553 - 561.

[2074] Temple, J. L., Dewey A. M., & Briatico L. N.
(2010).  Effects of Acute Caffeine Administration on Adolescents.
Experimental and Clinical Psychopharmacology. 18(6), 510 - 520.