Coffee has been studied extensively, and for most adults the news is reassuring. Large observational studies link moderate coffee intake (around 3 to 4 cups a day) to lower risks of type 2 diabetes, Parkinson's disease, liver disease, and even slightly lower overall mortality. It's also a major source of antioxidants in many diets.
There are caveats. Caffeine can disrupt sleep if you drink it late, raise anxiety in sensitive people, and temporarily nudge blood pressure. Pregnant people are advised to limit caffeine. And what you add matters — a drink loaded with syrup and cream is a different thing from black coffee. Enjoyed sensibly, coffee is fine for most people.