There's an older dementia study that said 3-5 cups a day kept the disease at bay but a newer dementia study said coffee of 6 cups a day in perpetuity was bad for your brain overall.
I think if you look at both studies they say less than 3 cups does pretty much nothing cognitively long term.
>>21394818Coffee is generally considered good in the literature for lower GI, upper GI is a more mixed bag since people argue about the increased acidicy being good/bad.