The Full Story
Vitamin D, along with calcium, is essential for developing and maintaining strong bones and muscles. It is sometimes called "the sunshine vitamin" because our bodies manufacture vitamin D when we're out in the sun. Other sources of vitamin D are fortified milk, fortified juice, fatty fish, and beef liver. Multiple vitamin preparations contain vitamin D, as do vitamin D supplements and calcium supplements with added vitamin D.
Recently, the Institute of Medicine (IOM) reviewed and revised recommendations for vitamin D. The recommended daily intake has been increased for most age groups, but not as much as some health professionals called for.
Over the past few years, some researchers have associated low levels of vitamin D with a number of chronic illnesses. Cancer, heart disease, arthritis, multiple sclerosis, arthritis, diabetes, depression, and asthma are among them. Based on these studies, the popular press has joined some health professionals in promoting widespread testing for vitamin D deficiency and for substantial vitamin D supplementation.
It is possible to measure forms of vitamin D in the bloodstream, though not all methods are standardized. IOM noted that there are no accepted standards for assessing "low" vitamin D levels; what's considered inadequate in some studies is adequate or even excessive in others. IOM also noted that research findings about the health consequences of low vitamin D are not consistent. In some cases, the findings are contradictory.
There is agreement that large excess intake of vitamin D over a long period of time can cause vitamin D poisoning, although this is uncommon. Effects can include nausea, vomiting, painful muscles, kidney damage, and high blood pressure. In one case, a child was given large amounts of an imported vitamin D supplement; in others, adults took supplements that contained much more than the labeled amount of Vitamin D.
The IOM panel recognized that it can be hard for people to obtain all of the vitamin D they need through foods, as there are limited food sources. Also, exposure to sunlight, the traditional source of vitamin D, must be limited to decrease the risk of skin cancer. There are groups of people who are unable to achieve much sun exposure anyway: people with dark skin; those who live at northern latitudes; elderly people who have higher requirements; and people who are unable to spend time outdoors, for example, patients in nursing homes. For many, vitamin D supplements are necessary for bone health and muscle strength.
A summary of the new recommendations for vitamin D and calcium supplementation can be found on the National Academies of Sciences Engineering Medicine website. The table provides the recommended intake for different age groups. Also provided is the maximum that can be taken daily without a risk of toxicity.
Anyone considering taking higher doses of vitamin D should do so only with the recommendation and supervision of a health professional. As with all medicines, vitamin D supplements should be stored safely out of children's reach. A large one-time dose should not cause harm, but a child who regularly swallows large amounts could be at risk of poisoning.
For questions about vitamin D poisoning, or if you suspect that someone has taken a large amount, use the webPOISONCONTROL® online tool for guidance or call Poison Control right away at 1-800-222-1222.
Rose Ann Gould Soloway, RN, BSN, MSEd, DABAT emerita
Barrueta F, Wang-Flores HH, Howland MA, Hoffman RS, Nelson LS. Acute vitamin D intoxication in a child. Pediatrics 2005; 115:e453-e456.
Chowdhury R, Kunutsor S, Vitezova A, Oliver-Williams C, Chowdhury S, Kiefte-de-Jong JC, Khan H, Baena CP, Prabhakaran D, Hoshen MB, Feldman BS, Pan A, Johnson L, Crowe F, Hu FB, Franco OH. Vitamin D and risk of cause specific death: systematic review and meta-analysis of observational cohort and randomised intervention studies. BMJ 2014;348:g1903 doi: 10.1136/bmj.g1903 (Published 1 April 2014).
Holick MF. Vitamin D deficiency. N Engl J Med 2007;357:266-81.
National Research Council. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academies Press, 2011.
Theodoratou E, Tzoulaki I, Zgaga L, Ioannidis JPA. Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of observational studies and randomized trials. BMJ 2014;348:g2035 doi: 10.1136/bmj.g2035 (Published 1 April 2014).