The Department of Energy recommends maintaining your refrigerator temperature close to 37⁰ F. A temperature of 37⁰ F is cold enough to keep food fresh without freezing. Colder than that is overkill and a waste of energy. Refrigerators can account for as much as 7% of residential energy consumption, so keeping the temperature only as cold as needed helps prevent using more energy than necessary to preserve your food.
Get more information from the Department of Energy:
photo by Susan O'Donnell