Vitamin D is a fat-soluble vitamin that is converted to its active hormone form in the body where it has several important roles. Vitamin D maintains bone health, nervous system, muscle and immune functioning, and helps reduce inflammation. Plus, vitamin D regulates many genes that modulate cell functioning.
Vitamin D Promotes Bone Health
There are vitamin D receptors throughout the body and science is still uncovering all of the important functions of this vitamin as well as consequences associated with insufficient and deficient levels of vitamin D.
However, vitamin D’s role in both health is very well established. Vitamin D helps the body absorb calcium and maintain adequate blood concentrations of both calcium and phosphate. Calcium and phosphate in the blood are both used to mineralize bone. Also, vitamin D is necessary for bone remodeling – the process through which old bone tissue is replaced with new bone over several months.
Too Little Vitamin D?
Insufficient levels of vitamin D can lead to bones that are thin, brittle and misshapen while also increasing risk of fractures, particularly of the wrist, hip, vertebrae and forearm. Children who are deficient in vitamin D may suffer from rickets whereas adults can develop osteomalacia. Both diseases are characterized by softening of the bones and skeletal deformities. In the early 1900s over 80% of children in the U.S. suffered from rickets. However, use of UV radiation or sunlight, vitamin D-rich cod liver oil and consumption of UV-irradiated milk helped eradicate rickets.
In recent years physicians are seeing a reemergence of this disease due to widespread vitamin D deficiency and insufficiency. And though adults may develop osteomalacia from short-term vitamin D deficiency, adults who have insufficient or deficient levels of vitamin D over the course of a lifetime have an increased risk of developing the brittle bone disease osteoporosis. Osteoporosis is characterized in low bone mass (hardness of the bones) and a breakdown in bone structure resulting fragile bones that are more likely to develop fractures. And though calcium is the primary nutrient that keeps bones strong, sufficient levels of vitamin D are necessary for optimal calcium absorption which makes this nutrient essential for osteoporosis prevention.
What foods contain vitamin D?
Vitamin D is found naturally in very few foods. Excellent natural sources of vitamin D include:
- Tuna fish
However, vitamin D is also fortified in milk and some milk alternatives such as soy or almond milk, ready-to-eat cereals, yogurts, nutrition bars, nutrition shakes and powders.
Did you know? In addition to consuming vitamin D in the diet, the human body can make it upon exposure to the sun’s UVB rays. However, darker skin pigment, shade, cloud cover, smog, sunscreen and age all impact how much vitamin D a person can produce. Also, people living in Northern states are not exposed to enough sunlight during the winter months to produce adequate levels of vitamin D in the body.
Many people are deficient in vitamin D or have insufficient levels of this vitamin due to poor intake, limited sunlight exposure, a decreased absorption of vitamin D or impaired ability to convert it to its active form. Adults at risk of developing insufficient or deficient levels of vitamin D include:
- Those with darker skin
- Adults over 50 years of age (due to an age-related decrease in the body’s ability to convert vitamin D to its active hormone form)
- People who avoid sunlight
- People who suffer from fat mal-absorption
- Obese individuals
Due to recently reported widespread vitamin D deficiency and insufficiency, some experts recommend routine vitamin D testing for those at risk, though you should not take more than the RDA unless otherwise directed by a physician.
Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press, 2010. Retrieved from: http://www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D.aspx January 27, 2013.
Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr 2004;79(3):362-371.
Vitamin D Dietary Supplement Fact Sheet. Office of Dietary Supplements, NIH.Retrieved from: http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ January 27, 2013.
Raiten DJ, Picciano MF. Vitamin D and health in the 21st century: bone and beyond. Executive summary. Am J Clin Nutr 2004;80:1673S-1677S.
Holick MF. The vitamin D deficiency pandemic: a forgotten hormone important for health. Public Health Reviews 32:267-283. Retrieved from: http://www.publichealthreviews.eu/upload/pdf_files/7/15_Vitamin_D.pdf January 27, 2013.