The scientists measured the antioxidant content of more than 100 different food items, including vegetables, fruits, nuts, spices, oils and beverages, and then examined national data on the contribution of each food item to the average American's diet.
Both caffeinated and decaffeinated coffee emerged as the biggest source of antioxidants, given that Americans do not eat sufficient quantities of fruit and vegetables. Black tea came second, followed by bananas, dry beans and corn.
Helping to rid the body of free radicals, destructive molecules that damage cells and DNA, antioxidants have been linked to a number of benefits, including protection against heart disease and cancer.
The research is the latest in a number of studies to suggest coffee could be beneficial, with consumption linked to a reduced risk of liver and colon cancer, type two diabetes, and Parkinson's disease.