Vitamin D, one of the 13 essential vitamins, helps the body absorb calcium, supports the immune system, aids in normal nerve and muscle function and regulates the production of proteins important for the development and growth of cells. Although the body stores vitamin D in the liver and fatty tissues, the Food and Nutrition Board established an adequate intake level of vitamin D for women that represents the amount sufficient to maintain bone health and normal calcium levels, according to the National Institutes of Health Office of Dietary Supplements.
Women between the ages of 19 and 50, even those pregnant or lactating, should receive 200 IU of vitamin D per day, according to the University of Maryland Medical Center. As women age, the bones become weaker and osteoporosis, known as porous bone disease, can set in. Therefore, the requirement for vitamin D increases to 400 IU for those women ages 51 to 70 and 600 IU for those over the age of 70.
Natural Dietary Sources
Since few foods naturally contain vitamin D, consuming the daily requirement through dietary sources can be difficult. Because animals store vitamin D in the liver and fatty tissues, some fish, including salmon, mackerel and tuna, contain natural vitamin D. Cod liver oil and beef liver also provide vitamin D. Other natural food sources include egg yolks and some mushrooms exposed to the sun's ultraviolet rays.
To help women meet their daily requirement of vitamin D, food manufacturers add vitamin D to some foods. In the United States, almost all milk is fortified with 100 IU per cup, which provides 50 percent of the adequate intake for most adults under the age of 50, according to the National Institutes of Health Office of Dietary Supplements. Other foods fortified with vitamin D include orange juice, breakfast cereals, yogurt and margarine.
Most men and women obtain their daily requirement of vitamin D through sun exposure. The ultraviolet rays from the sun penetrate the skin, triggering the conversion of 7-dehydrocholesterol to previtamin D3, which, in turn, becomes vitamin D3. Although women have become conscious of sun exposure and apply sunscreen, they usually fail to apply enough or cover all the skin, still allowing the ultraviolet rays penetrate the skin to produce vitamin D. The National Institutes of Health Office of Dietary Supplements reports that women only need 5 to 30 minutes of sun exposure twice a week to meet the daily requirement of vitamin D.
Vitamin D exists in several different forms, including ergocalciferol, also known as vitamin D2, and cholecalciferol, commonly called vitamin D3. Once ingested, the kidneys convert these forms into the active vitamin D, known as calcitriol, that the body can utilize. Vitamin supplements and vitamins used to fortify foods often use vitamin D2 derived from yeast. Although thought to be equivalent, vitamin D3 may be more potent than vitamin D2 and, therefore, provide better protection against vitamin D deficiency and associated bone diseases, according to research published by Lisa Houghton and Reinhold Vieth in the October 2006 issue of the "American Journal of Clinical Nutrition."