Even if you're drinking calorie-free black coffee, you should stick to a moderate intake to avoid taking in too much caffeine. While small amounts of caffeine might boost thermogenesis, too much can make you jittery, interrupt your sleep and cause anxiety, depression or a fast heart rate. The FDA recommends up to 400 milligrams — approximately 4 to 5 cups of coffee daily — as the recommended upper limit for caffeine intake. If you're drinking more than 3 cups daily, choose decaf coffee for the extra cups.
A 28-year study, eventually published in 2017 in Alzheimer's and Dementia, the journal of the Alzheimer's Association, determined that four to five cups of a coffee a day – a level deemed "moderate" – led to a decreased risk of dementia during that time period. Those who drank coffee in moderate levels had less medial temporal atrophy, which is linked to Alzheimer's disease, compared to those who drank three or fewer cups a day, including those who didn't drink any.