Vitamin D helps you absorb calcium for strong bones, supports your immune system in fighting off harmful bacteria and viruses, aids communication within your nervous system and keeps your muscles working smoothly. According to the Office of Dietary Supplements, or ODS, children and adults up to 70 years of age need to take in at least 600 IU of vitamin D daily. Older adults need at least 800 IU, as they are less able to absorb calcium efficiently, so are more at risk of osteoporosis, or brittle bones. Vitamin D deficiency may also affect thyroid functioning.
Meeting Your Vitamin D Needs
The most common food sources of vitamin D are some types of fish, such as salmon, tuna and mackerel, and fish liver oils. Beef liver, cheese and egg yolks also provide small amounts of this nutrient. Vitamin D is in few foods, so many people meet their needs through supplements or fortified foods. In the U.S., producers fortify most milk with 100 IU of vitamin D per cup; Canadians get 35 to 40 IU per 100 ml of milk. Breakfast cereals and some brands of orange juice and yogurt may also have vitamin D fortification. Vitamin D is the "sunshine vitamin," because your skin synthesizes it after exposure to the sun's ultraviolet rays. Many health care providers warn against prolonged exposure to the sun, however, because of its link to serious skin cancers. The American Academy of Dermatologists recommends you get all of your vitamin D from food sources and supplements, rather than risking skin cancer by exposure to UV light.
Vitamin D Deficiency Risk Factors
Researchers don't all agree on the optimal amount of vitamin D needed for good health. The Linus Pauling Institute, or LPI, suggests a minimum of 800 IU as a more appropriate daily reference intake of the vitamin. With that number in mind, LPI says at least a billion people worldwide are vitamin D deficient. No matter which standard you use, older age, darker skin, obesity and some malabsorption conditions, such as cystic fibrosis and Crohn's are risk factors for vitamin D deficiency. LPI includes those who do not receive enough direct sunlight in the high-risk category. If you need help in finding appropriate ways to meet your daily requirement of vitamin D, talk to a registered dietitian.
Vitamin D and Hyperthyroidism
Hyperthyroidism occurs when your thyroid gland overproduces the hormone thyroxine. When this happens, your metabolism may speed up, causing sudden weight loss, anxiety and rapid heart palpitations among other symptoms. Graves disease is a common cause of hyperthyroidism. If you have hyperthyroidism and you are not getting enough vitamin D, you are at greater risk for osteoporosis, or brittle bones, according to a study reported in the fall 2010 issue of the "Journal of Clinical Denistometry." An animal study reported in the July 2008 issue of "Endocrinology" also appears to implicate vitamin D deficiency in the development of hyperthyroidism.
Vitamin D and Hyperparathyroidism
The parathyroid glands are four small glands situated around your thyroid gland. These glands produce the parathyroid hormone PTH, which helps regulate calcium and phosphorus in your body. Hyperparathyroidism is when your parathyroid puts out too much PTH, causing the amount of calcium in your bloodstream to rise. If deficient in vitamin D, you may end up with secondary hyperparathyroidism. This happens because your parathyroid doesn't detect adequate amounts of calcium in the bloodstream, so it increases production of PTH, which then draws calcium from your bones, putting you at a greater risk of fractures.
References
- Office of Dietary Supplements: Vitamin D
- American Academy of Dermatology: Dermatologists can help separate fact from fiction for sun exposure, sunscreen and vitamin D
- Linus Pauling Institute: Vitamin D
- Mayo Clinic: Hyperthyroidism
- "Journal of Clinical Densitometry"; Hypovitaminosis D and bone mineral metabolism and bone density in hyperthyroidism; DK Dhanwal, et al; Oct-Dec 2010
- "Endocrinology"; Vitamin D deficiency modulates Graves' hyperthyroidism induced in BALB/c mice by thyrotropin receptor immunization; A Misharin, et al; Feb 2009
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