The three most common varieties of lettuce--romaine, butterhead, and crisphead--provide varying amounts of vitamins. Generally, the darker the lettuce, the more nutrients it contains. Romaine lettuce scores high for vitamin content; World's Healthiest Foods endorses it as a food that is heart-healthy, and lists it as an excellent source of certain vitamins. Butterhead lettuce, which includes Bibb and Boston varieties, provides less vitamins, but is still a good source of some. Iceberg lettuce, which provides negligible amounts of vitamins, is at the bottom of the list.
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Two cups of romaine lettuce are an excellent source of vitamin A. With 2912 IU, this serving contains 58 percent of the recommended daily value, based on a 2,000-calorie diet. Romaine lettuce also contains 1747mcg of beta carotene, which turns into vitamin A in your body. The World's Healthiest Foods notes that romaine lettuce contains 26.88mg of vitamin C, making it a very good source of this important antioxidant vitamin, which works with beta-carotene to prevent the oxidation of cholesterol, helping to prevent plaque formation on artery walls. The website also credits romaine with being a very good source of folate, with 151.98mcg, and of vitamins B1 and vitamin B2; 2 cupfuls of romaine contains .11mg. each of these B-complex vitamins. Romaine lettuce is also rich in potassium, delivering 114mcg per 2 cup serving.
Boston and Bibb Lettuce
Buttterhead lettuce, which includes the popular Boston and Bibb varieties, has large, sweet-flavored, tender leaves. According to the National Agricultural Library of the United States Department of Agriculture, Bibb lettuce contains 73mcg of folate per 100g, and 3312 IU of vitamin A.
Crisphead lettuces, such as iceberg, feature green leaves on the outside and a whitish interior. According to Ralph Ofcarcik, Ph.D., Director of Nutrition Services at Red Mountain Spa in St. George, Utah, iceberg lettuce richly deserves its reputation as an inferior source of nutrition. It ranks last among all lettuces in vitamin A and vitamin C content, as well as thiamine, riboflavin, pantothenic acid, B6 and vitamin E. According to the National Agricultural Library of the United States Department of Agriculture, 100g--or roughly 3 oz.--of iceberg lettuce does provide 2.8mg of vitamin C, plus .041mg of thiamine.