Prevalence
Although exact rates of prevalence are not available, general population data shows a 0.002% prevalence over a year-long period and higher prevalence within clinical populations. Caffeine
Caffeine is a methylxanthine, and is hydrophobic. The structure of caffeine allows the molecule to pass freely through biological membranes including the blood-brain barrier. Absorption in the gastrointestinal tract reaches near completion at about 99% after only 45 minutes. Half-life of caffeine for most adults is between 2.5 and 4.5 hours when consumption is limited to less than 10 mg/kg. However, during neonatal development, half-life for the fetus is significantly longer and decreases exponentially after birth to reach a normal rate at about 6 months. Cytochrome P-450, a hemeprotein, acts in liver microsomes to metabolize caffeine into dimethylxanthines, monomethylxanthines, dimethyl uric acids, monomethyl uric acids, trimethylallantoin, dimethylallantoin, and derivatives of uracil. Most caffeine is metabolized by 3-methyl demethylation, forming the metabolite of paraxanthine. Many metabolites, in addition to caffeine, act within the body and are partly responsible for the physiological response to caffeine. Mechanism of caffeine action
Caffeine acts in multiple ways within the brain and the rest of the body. However, due to the concentration of caffeine required, antagonism of adenosine receptors is the primary mode of action. The following mechanisms are ways in which caffeine may act within the body, but depending on necessary caffeine concentration and other factors may not be responsible for the clinical effects of the substance.
This stress signal begins at the level of the hypothalamus in the brain and undergoes subsequent amplifications throughout the body. This system elevates levels of stress hormones in the blood, which results in the body shutting down secondary bodily processes and increasing alertness to better prepare for response to the perceived threat. Studies show that activation of this pathway is correlated with anxiety-like behaviors, including panic, post-traumatic stress, and generalized anxiety disorders, as well as depression. Rodent studies show that caffeine consumption in adolescence results in dysregulation of HPA axis function as well as central nervous system response, which impairs the bodys response to stressful stimuli.In cases of prolonged consumption of excess amounts of caffeine, studies show that individuals exhibit a reduced response to HPA axis activation by the hormone ACTH and a generalized increase in basal levels of stress hormone corticosterone. Researchers concluded that the sensitivity of adrenal glands to ACTH is diminished by caffeine consumption. People diagnosed with panic disorder show less HPA activity following stressful stimuli than their healthy control counterparts. Susceptible populations
Caffeine has varying effects on anxiety across given populations. The populations most susceptible to caffeine-induced anxiety disorder include those already diagnosed with an anxiety disorder and adolescents. Adolescents, particularly, are at increased risk for developing anxiety disorders and anxiety-related symptoms. While few human studies have been done to investigate this connection, many rodent studies show a correlation between caffeine consumption in adolescence and increased anxiety.