According to the University of Maryland Medical Center, many adults are not getting their recommended daily amount of vitamin D. Those who live in northern climates, with reduced exposure to sunlight, or who are darker skinned are particularly at risk for deficiency. Approximately 54 percent of African-American women and 42 percent of Caucasian women living in the northern United states have low levels of vitamin D. Getting enough vitamin D means accessing sunlight and consuming foods both naturally high in vitamin D and foods enriched with the vitamin.
Functions
Of the several types of vitamin D, two forms are important to humans: vitamin D2 and D3. Vitamin D2, also known as ergocalciferol, is synthesized by plants and is found in plant-based foods. Vitamin D3, cholecalciferol, is synthesized by humans through skin exposure to ultraviolet-B rays from the sun. According to the Mayo Clinic, vitamin D's major function is to regulate blood levels of phosphorus and calcium. It may also help provide protection from cancer, hypertension, osteoporosis and several autoimmune diseases.
Vitamin D, Calcium and Phosphate
Vitamin D promotes the absorption of calcium in the digestive system. Eating vitamin D-rich foods with calcium-rich foods can increase the bioavailability of the calcium. Vitamin D also manages the levels of calcium and phosphate in your body, allowing for normal growth and maintenance of the mineral structures in your bones. In older adults, vitamin D and calcium work together to help prevent osteoporosis.
Vitamin D and Vitamin K
High intakes of vitamin D appears to suppress the normal functions of vitamin K by stimulating proteins that require vitamin K to metabolize properly. This heightened demand for vitamin K depletes the body's store of the nutrient. Vitamin K is needed for blood coagulation, bone development and structural maintenance and nervous system functions. Vitamin A may protect against vitamin D toxicity by suppressing the activity of the same proteins vitamin D stimulates. Talk with your doctor before taking vitamins D, K and A together in high doses or combined with any medications.
Interactions with Medications
Taking vitamin D while taking certain medications can affect your ability to absorb vitamin D or calcium. Antacids and cholesterol-reducing drugs in the statins family may reduce the amount of vitamin D you absorb. Medications sometimes prescribed for heart disease or high blood pressure, called calcium channel blockers, prevent calcium from entering heart and blood vessel cells and can also slow production of vitamin D in the body. Thiazide, a medication use for edema and high blood pressure, increases calcium reabsorption and can overstimulate vitamin D metabolism. This can lead to hypercalcemia, which can cause fever, chills, vomiting or hypertension.
References
- Mayo Clinic; Vitamin D; July, 2011
- University of Maryland Medical Center; Vitamin D; June, 2010
- National Institutes of Health: Vitamin D
- Medline Plus; Vitamin D; February, 2011
- Mayo Clinic; Calcium Channel Blockers; December 2010
- University of Washington Osteoporosis and Bone Physiology; Thiazide; March 2006
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