The results identified an association between coffee and several important markers related to Alzheimer's.
Dr. Gardener said: "We found participants with no memory impairments and with higher coffee consumption at the start of the study had a lower risk of transitioning to mild cognitive impairment - which often precedes Alzheimer's - or developing the disease over the course of the study."
The beverage was also linked to slowing accumulation of amyloid beta - toxic proteins that clump in plaques, killing neurons.
Dr. Gardener described the findings as "encouraging," suggesting coffee is an easy way to stave off the devastating neurological condition.
The number of cases worldwide are set to triple in the next 30 years due to aging populations.
If you only allow yourself one cup a day, the study indicates you might be better off treating yourself to another.
Dr. Gardener said: "If the average cup of coffee made at home is 240g, increasing to two cups a day could potentially lower cognitive decline by eight percent after 18 months.
"It could also see a five percent decrease in amyloid accumulation over the same time period."
The study adds to evidence coffee is good for the brain. It is rich in caffeine and plant chemicals called flavonoids that increase blood flow.
But a maximum number of daily cups that provided a beneficial effect could not be established.
The analysis was also unable to differentiate between caffeinated and decaffeinated coffee, brewing methods and the presence of milk or sugar.
Dr. Gardener said the relationship between coffee and brain function was worth pursuing.
She added: "We need to evaluate whether coffee intake could one day be recommended as a lifestyle factor aimed at delaying the onset of Alzheimer's."
Scientists are yet to determine precisely which constituents of coffee are behind its seemingly positive effects on brain health.
Caffeine, a natural compound that stimulates the brain and nervous system, is suspected of being the main contributor.
But preliminary research has found 'crude caffeine,' a by-product of decaffeinating coffee, decreases memory impairment in mice.
Other components such as cafestol, kahweol and EHT (Eicosanoyl-5-hydroxytryptamide) have also been implicated in animal experiments.
Coffee is America's most popular drink with about 400 million cups being consumed every day