Moderate doses of caffeine, the equivalent of five to seven cups of coffee, over the course of seven days suppresses the growth of new neurons in the hippocampus, an area of the brain involved in learning and memory, according to a published study.
But extremely high “beyond physiologically plausible dosages” have the opposite effect — they temporarily increase the growth of new nerve cells in the hippocampus.
“Extended, but not acute caffeine treatment depresses proliferation at moderate doses and increases proliferation at high doses, suggesting that its effects are mediated through complex and potentially indirect pathways,” Christian T. Wentz and Sanjay S.P. Magavi of MIT write in their study.
The growth of new neurons in the hippocampus, a process known as neurogenesis, continues through adulthood in mammals and is associated with memory and learning processes.
“Unexpectedly, doses of caffeine that are thought to have generally positive effects on attention and activity depress neurogenesis in the adult hippocampus,” Wentz and Magavi say. “It will be particularly interesting, and potentially therapeutically useful, to examine how the multiple pathways influenced by caffeine interact to modulate hippocampal neurogenesis.”
One possible pathway through which moderate and high doses of caffeine may influence neurogenesis is by affecting behavior.
Moderate doses of caffeine may cause decreased proliferation of new neurons by causing sleep deprivation and increasing anxiety. On the other hand, the increased physical activity caused by high doses of caffeine may cause increased neurogenesis.
Learning tasks, enriched environments, running, and antidepressants have been shown to increase neurogenesis while stress and sleep deprivation have been found to depress it.
However, the influence caffeine has on neurogenesis could be caused by the way it affects blood vessels or through a yet-to-be discovered mechanism, Wentz and Magavi note.
For their study, Wentz and Magavi administered various doses of caffeine to mice for seven days and examined its effects on the neurons in the hippocampus.
The study was published in volume 56 of Neuropharmacology in 2009.