Iceberg Lettuce Reduces Hip Fracture Risk

A large prospective study shows for the first time that vitamin K lowers the risk of hip fracture among middle-aged and older women. Even more surprising, it demonstrates that iceberg lettuce has nutritional value. Vitamin K, found mainly in lettuce, is required to form the bone protein osteocalcin and may also reduce calcium excretion and bone loss. Researchers suspected it might also protect against osteoporosis in postmenopausal women.

As part of the Nurse's Health Study, 12,700 women aged 38 to 63 filled out dietary questionnaires in 1984, 1986 and 1990. By 1994, 270 of the women with a median age of 62 had fractured their hips. Diane Feshkanish, M.D., of Harvard Medical School found that the 20 percent of women who consumed less than 109 mcg of vitamin K a day had a 43-percent higher hip fracture risk. The other 80 percent of women had the same fracture risk regardless of their vitamin intake. Thus, postmenopausal women may need a minimum of 109 mcg vitamin K each day—considerably higher than the RDA of 65 mcg.

The women got their vitamin K from iceberg lettuce (29 percent), broccoli (15 percent), spinach (18 percent), romaine lettuce (6 percent), brussels sprouts (5 percent) and greens (4 percent). Women who ate lettuce each day had only 55 percent the risk of hip fracture as those who ate it once a week. Very few took supplemental vitamin K. The women's median daily vitamin K intake was 163 mcg, much more than the 59 to 82 mcg found in general population surveys.

Vitamin K had a pronounced effect in women who had never used estrogen, but no effect in current estrogen users. This may be because estrogen, like vitamin K, strengthens bones.

—American Journal of Clinical Nutrition, 1999 Jan;69:74-9