Drinking coffee with sugar increases your diabetes risk, especially type 2 diabetes. Some studies have found that people who drink black coffee without sugar have a 23 to 50 per cent lower risk of getting this disease  ,  ,  . Diabetic people should also avoid sugar-laden coffee as they cannot secrete enough insulin, and drinking coffee with sugar causes the sugar to accumulate in the blood.
Again, it's the caffeine working here. Your recommended maximum amount of caffeine is 400 milligrams, roughly the amount that you’ll get from 4 cups of coffee. If you’re caffeine-sensitive, be careful with coffee. You are probably already aware what amount and what kind of coffee suits, or doesn't suit you. The amount of caffeine that is safe for human consumption is actually written in our DNA.
Some health benefits of coffee come from the beverage's caffeine content and not necessarily from the coffee itself. For example, the review of studies published in Australian & New Zealand Journal of Psychiatry determined there was also a nonlinear association between caffeine and a lower risk of depression, in addition to the link with coffee itself. Caffeine, a stimulant, also has a beneficial effect on athletic performance, with research published in 2016 in the Journal of Sports Science determining that dosing with caffeine prior to physical activity increased "vigor" and decreased fatigue. To use this to your benefit before working out, drink a cup of black coffee about 30 to 45 minutes before you begin exercising.