> Scientists don’t know exactly what makes coffee so beneficial, Dr. Goldberg said, but the answer may lie in its antioxidant properties, which can prevent or delay cell damage. Coffee beans contain high amounts of antioxidants, said Beth Czerwony, a registered dietitian at the Cleveland Clinic’s Center for Human Nutrition in Ohio, which can help break down free radicals that cause damage to cells. Over time, a buildup of free radicals can increase inflammation in the body, which can cause plaque formation related to heart disease, she said, so dietitians recommend consuming foods and beverages that are rich in antioxidants.

> There’s also the possibility that coffee drinkers tend to make healthier choices in general. They might opt for a cold brew or a cup of drip coffee instead of a less healthy source of caffeine, like an energy drink or soda, Dr. Goldberg added. “If you’re pounding Mountain Dew or Coca-Cola or Red Bull or all these other drinks, they have tons more sugar, all the artificial stuff — versus coffee, which is a generally unprocessed food.”

(Side note: if someone else read this and started drinking coffee because of it, they'd probably be replacing an existing beverage choice as well. IOW, even if substitution effect was the cause or a contributing factor, people acting on the conclusions may still see the effect – and certainly would at public-health scale.)