Vitamin D is necessary to help your body process calcium and phosphate to keep your bones and teeth strong, while maintaining proper levels of these nutrients for other uses. This vitamin also has a role in the immune and neurological systems, cell growth and inflammation reduction. The vitamin D you get from the sun and through the foods you eat can’t be used until it is processed by the liver and kidneys. While research on vitamin D depletion is lacking, much attention has been given to vitamin D deficiency.
Your Daily Requirement of Vitamin D
According to the Office of Dietary Supplements, or ODS, children and adults up to 70 years old need to take in at least 600 International Units, or 15 micrograms, of vitamin D daily. Only a few foods are natural sources of this vitamin, including oily fish, such as salmon, mackerel or tuna; eggs; cheese; and beef liver. Some dairy products, such as milk and yogurt, as well as orange juice and many breakfast cereals are fortified with vitamin D. In the U.S., the requirement for milk is 100 International Units per cup, while in Canada, it’s 35 to 40 International Units per 100 milliliters. Though still controversial, some health researchers, such as those at the Linus Pauling Institute, recommend that an adult dose of up to 2,000 International Units, or 50 micrograms, of supplemental vitamin D daily.
Those at Risk for Vitamin D Deficiency and Depletion
The ODS recommendation for older adults is at least 800 International Units, as they are less able to absorb calcium efficiently and are more at risk for osteoporosis, or brittle bones. People who have Crohn’s or other malabsorption syndromes also might not be able to effectively use vitamin D. Some people, such as the elderly who live in nursing homes or babies, might not get enough direct sunlight to help them produce vitamin D. Chronic liver disease and kidney failure are also risk factors for vitamin D deficiency, as these damaged organs might not be able to process the inert vitamin D into the useful form of the nutrient. Obesity and dark skin are other risk factors.
Symptoms of Vitamin D Deficiency
A blood test is used to determine your vitamin D level. Tests are available for two different forms of vitamin D, but most people only need to get the less-expensive 25-hydroxyvitamin D, or 25(OH)D, test, according to Dr. Susan Ott, professor of medicine at the University of Washington. An optimal level of circulating 25-hydroxyvitamin D is 20 to 50 nano grams per milliliter; 8 to 20 nano grams per milliliter is insufficient, while a number lower than 8 nano grams per milliliter is considered deficient.
Your bones can become brittle or soft if you’re deficient in vitamin D over a period of time. People who have only a mild deficiency might have muscle pain and weakness. As the deficiency worsens and your calcium levels deteriorate, you might also experience numbness or neuromuscular pain, muscle cramps, spasms in your throat muscles and even seizures. If you have such symptoms, your doctor might prescribe larger doses of supplemental vitamin D.
Vitamin D Toxicity
It is also possible to take too much vitamin D. The ODS reports tolerable upper intake levels of 4,000 International Units for both males and females over the age of 9, with toxic levels at 10,000 to 40,000 International Units per day, or 200 to 240 nano grams per milliliter of vitamin D in your bloodstream. Anorexia, weight loss, excessive urination and heart arrhythmias have all been reported in people with vitamin D toxicity. The biggest concern, though, is that chronically elevated levels of vitamin D might cause you to have more calcium in your bloodstream, which can lead to kidney stones or damage to your heart or kidneys due to calcification of your blood vessels and tissues.