Image Number K9834-1
After determining the role of vitamin A in maintaining sight, researchers determine adults should consume a minimum of 5,000 to 6,000 international units of vitamin A per day. Later, in the 1970s, scientists at the Beltsville Human Nutrition Research Center discover that supplementing vitamin A with zinc helps prevent blindness. ARS has five other human nutrition centers in Boston, Massachusetts; Houston, Texas; Grand Forks, North Dakota; Davis, California; and Little Rock, Arkansas.
Photo by Keith Weller.