These include the reluctance of some mothers to breast feed their children and a lack of access to fortified foods.

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The Spina Bifida Association strongly backs the introduction of fortified foods.

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However, Andrew Russell, the executive director of the Spina Bifida Association, which strongly backs the introduction of fortified foods, dismissed the worries of the two scientists.

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Vitamin D is a fat-soluble vitamin that occurs naturally in a limited number of foods, so fortified foods including milk, margarines and breakfast cereals and dietary supplements are the major source for most Americans.

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Make sure to eat plenty of high-quality, lean protein like fat-free dairy, egg whites, fish and skinless chicken (protein should make up about 20 percent of your total calories) and limit vitamin A fortified foods or multivitamins with high doses of vitamin A, which can negatively impact bone health.

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If you hate fish, take a fish oil capsule or try out some of the new foods fortified with DHA including soy milk, yogurt and nutrition bars.

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Sally and Clare agree that up to three servings per day is safe, but they emphasize that soy should come from whole foods like soy milk, edamame and tofu, and that supplements like smoothies, bars and soy fortified cereals should be limited.

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