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On Nutrition

Strong Bones Have Another Ally: Vitamin K

September 02, 2002|AMANDA URSELL | SPECIAL TO THE TIMES

It is not just calcium-rich milk and dairy foods that count in the fight against osteoporosis, new research shows. Vegetable oils, liver, cauliflower and cabbage are also a vital part of a sound nutritional battle plan.

These foods are rich in vitamin K, a seldom-mentioned vitamin that scientists say aids in building strong bones and that may help protect against the threat of osteoporosis.

Just as our body produces some vitamin D--also needed for strong bones because it helps with calcium absorption--most of our body's vitamin K needs are met by bacteria in the intestines that produce this vitamin. What we don't get naturally must come from regular dietary sources. (The minimum daily requirements of vitamin K for adults is 65 micrograms for women and 80 micrograms for men.) But most Americans' intake of vitamin K is low or average; when intake is less than 50 micrograms a day, signs of inadequacy in bone health begin to show.

New research suggests that one reason many Americans get insufficient amounts of vitamin K may be linked to plant oils. These vegetable oils, including canola, soy and sunflower, should supply up to a third of our daily needs. But Americans' intake of these oils often comes from a hardened form of oil found in fast food, baked goods such as cookies and crackers, and vegetable margarine. The hardening process alters vitamin K, making it no longer available to the bone, says Sarah Booth, an assistant professor at Tufts University who heads the school's Vitamin K Research Laboratory.

To boost your intake of vitamin K, it's best to avoid eating too many processed foods and margarine and to ingest oils in their pure form--in salad dressings, for example. Foods richest in vitamin K are green vegetables such as broccoli, spinach, kale, cabbage and lettuce. Liver, oats and lentils provide smaller amounts of this vitamin.

Besides increasing your intake of vitamins and minerals, you may also want to avoid certain foods to help strengthen your bones. While whole-grain cereals are believed to offer many health benefits, unprocessed bran--which is often added to cereals--is not advisable. This is because whole-grain fiber contains substances called phytates that have been shown to reduce the body's ability to absorb and make beneficial use of calcium.

Enzymes in yeast used for baking bread destroy most of the phytates, as do food-processing methods that require heat, such as those used to make high-fiber whole-grain breakfast cereals. In raw bran, however, the phytates are still active and may potentially compromise calcium levels. Oxalic acid, a plant chemical present in rhubarb, has similar calcium-binding effects.

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Amanda Ursell, a dietitian and nutritionist, is a London-based freelance journalist. Her column appears on the first Monday of the month. She can be reached at amanda@ursell.com.

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