During Mansa Musas (ruler of the Mali Empire from 1312 to 1337) hajj to Mecca in 1324, he passed through Cairo in July 1324, and was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels where he gave away so much gold that it depressed the price in Egypt for over a decade, causing high inflation. A contemporary Arab historian remarked:

Gold was at a high price in Egypt until they came in that year. The mithqal did not go below 25 dirhams and was generally above, but from that time its value fell and it cheapened in price and has remained cheap till now. The mithqal does not exceed 22 dirhams or less. This has been the state of affairs for about twelve years until this day by reason of the large amount of gold which they brought into Egypt and spent there [...]. The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Mesoamerica, Peru, Ecuador and Colombia. The Aztecs regarded gold as the product of the gods, calling it literally "god excrement" (teocuitlatl in Nahuatl), and after Moctezuma II was killed, most of this gold was shipped to Spain. However, for the indigenous peoples of North America gold was considered useless and they saw much greater value in other minerals which were directly related to their utility, such as obsidian, flint, and slate.
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.