Chapter 8 - Caffeine

Methylxanthines

  • include

    • caffeine, theophylline, & theobromine

    • alkaloids

    • occur naturally in more than 60 species of plants

  • consumed in

    • beverages

      • coffee, tea

    • foods

      • chocolate

    • medications & street drugs

History

  • ancient uses

    • coffee and tea

  • 15th century: introduced to Europe

  • attempts to suppress coffee/tea drinking failed

    • arabia & egypt

    • europe

Usage

  • caffeine used around the world in nearly all cultures (90% consume regularly)

    • most preferred drug

    • US: 3x world average

      • < Canada & UK

    • most common: coffee, tea, and soft drinks

  • used by kids and adults

    • nearly all ages

    • effects on kids?

Effects on the Body

  • alert, focused, happy, energetic

  • raise blood pressure, make us anxious

  • stimulant for CNS, blocks sleep-inducing molecule (adenosine)

    • body gets energy by breaking down ATP, freeing ATP’s backbone Adenosine

    • adenosine docks to receptors → neurons fire more sluggishly & slow release of important brain-signaling molecules → makes you sleepy

    • caffeine = adenosine receptor antagonist → blocks adenosine receptors

    • when adenosine enters receptor, it can make it harder for dopamine (pleasure) to fit in its receptor, but caffeine does not do this so caffeine can also bring about positive feelings

  • reduces the risk of diseases (Parkinson’s, Alzheimer’s, some cancers)

  • ramp up ability to burn fat

  • increased urination or diarrhea, insomnia and anxiety

  • if you consistently use caffeine, your body creates more adenosine receptors so they can actually do their job → you need more caffeine to feel the effects

    • if you quit using caffeine, you will feel withdrawal effects like headaches

Pharmacology

  • sites of action

    • adenosine →

      • sedation

      • regulation of oxygen delivery

      • dilation of blood vessels

    • caffeine blocks adenosine receptors

  • pharmacokinetics

    • absorption

      • oral administration

    • distribution

      • rapid absorption & distribution

        • concentration similar throughout body

        • peak levels in 15-45 minutes

        • half-life of 2.5-7.5 hours

      • crosses blood-brain barrier and placenta

    • metabolism

      • liver enzymes

      • kidney excretion

      • affected by?

Tolerance & Dependence

  • tolerance

    • evidence conflicts

    • tolerance does occur to sleep and physiological functions

    • little tolerance to stimulant effects

  • dependence

    • pattern of usage may feel like a dependence

    • withdrawal

      • headache and fatigue

      • depression

      • lower alertness and energy

      • sleepiness and irritability

Acute Effects

  • physiological

    • CNS stimulation

    • heart muscle constraction

    • relax smooth muscles

    • diuretic effect on kidneys

    • elevates basal metabolism

  • mood

    • elevates mood

      • morning wake-up

      • self-medicate

  • performance

    • impairs decision-making

    • affects motor speed and accuracy

    • decreased eye-hand coordination

    • improved night driving vigilance

    • speeds reaction time

Interactions

  • coffee decreases smoking

  • smokers excrete caffeine faster

  • caffeine-alcohol combinations show state-dependent memory effects

Acute Toxic Effects

  • 2 cups of coffee

    • elevated mood

    • decrease fatigue

    • increase BP (slight), heart rate, GSR

    • more reactive

  • 7-10 cups of coffee

    • no added mood-elevating effects

    • insomnia, restlessness, mild sensory disturbances, muscle tenseness

      • caffeinism, anxiety attacks

  • caffeinism: caffeine intoxication

    • muscle twitching

    • rambling thoughts and speech

    • cardiac arrhythmia

    • psychomotor agitation

Chronic Effects

  • conflicting results in pregnancy

    • FDA: moderate doses have no negative effects on reproduction

  • no relationship with cancer or heart attack

    • unless you are slow to metabolize caffeine

  • negative

    • increased osteoporosis in post-menopausal women

    • increased serum cholesterol

    • indigestion

    • palpitations and tremor

    • headache and insomnia

  • positive

    • coffee may protect against liver cirrhosis

    • heavy coffee use may protect against hypertension

Recommendations

  • moderate consumption

  • pregnant women should keep consumption low

  • anxiety disorders may be aggravated by caffeine

Therapeutic Uses

  • part of cold and headache remedies

  • part of weight-loss medications

  • caffeine stimulates breathing in premature infants

  • theophylline (tea) dilates coronary arteries