Chapter 2 - Caffeine

Absorption

• Absorbed through linings of the stomach (slowly). Most absorbed through small intestine.

• Full effect: 30-60 min. (depending on food in stomach)

• Metabolized by liver; excreted through kidneys

• Half-life: approx 3 hrs.

Mechanism of Action

• Blocks adenosine receptors• Adenosine: inhibitor; caffeine prevents it from

working• 200 mg – brain arousal• 500 mg - + heart rate and breathing• Dilates blood vessels; constricts blood vessels

in the brain

Tolerance and Dependence

• Tolerance develops to some effects• Dependence-12-24 hrs. after last cup-

headaches and fatigue

Effects on the Body

• Heart: increase heart rate; irregular heart beat; heart disease: conflicting results; may increase blood pressure

• Cholesterol: may raise LDL (not filtered coffee)• Kidneys: contain adenosine receptors; diuretic• Digestive System: gastritis; contributes to

problems with ulcers (doesn’t cause them).• Respiratory System: Theophylline (asthma)

• Reproductive System: reduces chances of pregnancy; lower birth weight; fibrocystic disease

• Eyes: Constricts vessels, decreased nutrients• Stress: increases adrenaline (increased blood

pressure)• Panic Attacks: 700+ mg – panic attacks in

people who don’t have panic disorder

• Enhancement of Physical Performance: delays fatigue; may help muscle performance; mixed results from studies; fat burners?; may dehydrate

• Lowers calcium levels• Caffeine content – coffee p. 74• Caffeine content – energy drinks & soda p. 77• Caffeine content – over-the-counter drugs p. 78