Too much coffee. For most healthy adults, moderate consumption of coffee, 1-3 cups per day, would not be harmful. Regular coffee drinking may provide possible health benefits, including lower risk of type 2 diabetes, gallstones and parkinson’s disease. Caffeine contained in coffee, however, can cause insomnia, nervousness, acid reflux, tremors, palpitations, dehydration and irritability. Moderation is the key.