There are few downsides to drinking moderate amounts of coffee and many proven health benefits — though some researchers warn of the risk of bad breath and increased dry cleaning bills.

A large, Venti-sized epidemiological study of more than 400,000 older Americans showed that men who drank two to three cups of coffee per day were 10 percent less likely to die than those who didn't drink coffee, while women drinking the same amount were 13 percent less likely to die. Though it's unclear how coffee may influence longevity, the correlation is significant.

Other studies in recent years have shown moderate amounts of coffee — approximately three to four cups per day — were linked to a reduction in developing type 2 diabetes, basal cell carcinoma skin cancer, prostate cancer, oral cancer, and the recurrence of breast cancer.

Moreover, animal studies show that caffeine may influence brain chemistry to delay the onset of dementia. Last year, experimenters at the University of Illinois at Urbana-Champaign found that laboratory mice, briefly starved of oxygen, lost the ability to form memories. After catching their breath, half of the mice received a dose of caffeine equivalent to several cups of coffee. Those mice recovered 33 percent more quickly than those without caffeine.

Upon closer examination, investigators found that caffeine had disrupted the harmful effects of adenosine, a material inside cells that normally provides energy but is destructive when cells are damaged or stressed. The leaky adenosine may cause a biochemical reaction leading to inflammation, disrupting the function of brain cells and possibly contributing to brain damage, including the normal process of decline into dementia.

In another study in humans last year, investigators from the University of South Florida and the University of Miami tested the level of caffeine in blood from older adults with mild cognitive impairment, characterized by serious forgetfulness that may progress to full-blown dementia. When evaluated two to four years later, participants with lower levels of caffeine, or none at all in the bloodstream, had progressed further toward Alzheimer's than those who'd drank coffee.

Still, the elixir remains as mysterious as when the drink first emerged during the 13th to 15th centuries.

"We don't know whether blocking the action of adenosine is sufficient" to prevent or ease the effects of mental decline, said Dr. Gregory G. Freund, professor of pathology at the University of Illinois.

To date, researchers don't understand whether caffeine alone confers health benefits or whether it's a combination of the drug and other elements of coffee. Another study at the University of South Florida, in 2011, found that mice genetically predisposed to Alzheimer's failed to benefit much from caffeine alone — though no evidence exists to suggest health benefits from simply mixing caffeine with water and large amounts of sugar.

Until further study, the full benefits of the popular drink can be explained only by black magic — or cream-colored, depending upon how you like it. Coffee "has been popular for a long, long time," Freund said in an interview, "and there's probably good reasons for that."

Sources: Freedman ND, Park Y, Abnet CC, Hollenbeck AR, Sinha R. Association of Coffee Drinking with Total and Cause-Specific Mortality. New England Journal of Medicine. 2012.

Chiu GS, Chatterjee D, Darmody PT, et al. Hypoxia/Reoxygenation Impairs Memory Formation Via Adenosine-Dependent Activation of Caspase 1. Journal of Neuroscience. 2012.