Michael F. Holick, PhD, MD, Boston University School of Medicine
Catherine M. Gordon, MD, Hasbro Children’s Hospital
Vitamin D helps the body absorb calcium. Along with calcium, it is vital for strong, healthy bones. We normally get vitamin D through exposure to sunlight, which triggers the skin to make this vitamin. Very few foods naturally contain vitamin D. Milk and a few other beverages and foods are “fortified” with added vitamin D in some countries, such as the United States and Canada. You can also get vitamin D in supplements.
However, many people still do not get enough of this important vitamin. For instance, the skin makes less vitamin D as we age. Use of sunscreen or sun avoidance also lowers the skin’s production of vitamin D.
There has been much confusion about how much vitamin D we should get and what defines a deficiency, or lack, of this vitamin. This guide is based on The Endocrine Society’s practice guidelines for physicians about testing for, treating, and preventing vitamin D deficiency.
These guidelines do not apply to people who want to take vitamin D for reasons other than bone health. The guidelines do not recommend a high dose of vitamin D to try to prevent disease, improve quality of life, or extend life.
What health problems does low vitamin D cause?
Vitamin D that is too low often causes no symptoms at first. However, vitamin D deficiency can lead to a loss of bone density (size and strength), broken bones (fractures), muscle weakness, and the bone-thinning disease osteoporosis. Severe vitamin D deficiency can cause rickets in children and osteomalacia in adults. Both problems cause soft, weak bones, as well as pain in the bones and muscles.
Some studies show that a lack of vitamin D may raise the risk of some cancers and certain other health problems. However, there is not strong scientific proof of this yet.
What are the risk factors for vitamin D deficiency?
Some health problems raise the risk of vitamin D deficiency and suggest the need for vitamin D testing. They include:
Other risk factors for vitamin D deficiency are:
How is vitamin D deficiency found?
The best way for doctors to measure how much vitamin D is in your body is with a blood test called the serum 25-hydroxyvitamin D test. Not everyone should get this screening test. Experts recommend it for people at risk of vitamin D deficiency. Your doctor will tell you if you need this test.
A test result below 20 nanograms per milliliter (ng/mL) shows you do not have enough vitamin D.
You may need to repeat the 25-hydroxyvitamin D blood test during treatment of vitamin D deficiency. This will show your response to treatment.
How is vitamin D deficiency treated and prevented?
Treatment and prevention of vitamin D deficiency includes increasing your intake of vitamin D. The goal is to get your blood level of vitamin D above 30 ng/mL. You likely will need supplements to raise your vitamin D level. That is because it is hard to get enough vitamin D solely from your diet, and excess sun exposure can cause skin cancer.
In supplements and fortified foods, vitamin D comes in two forms: D2 and D3. While some research studies suggest that vitamin D2 may be less potent, either form can be effective at recommended doses.
Vitamin D comes in pills, gelatin capsules, or a liquid for children, alone or in a multivitamin. The oral dose is once daily or weekly. Children with rickets or at risk of this disease may get vitamin D injections (shots) a few times a year.
The treatment dose of vitamin D depends on your age, how low your blood vitamin D level is, and what is causing the level to be low. Most often your doctor will lower the vitamin D dose after six to eight weeks of treatment. You will then stay on this lower “maintenance” dose for as long as you need.
Vitamin D treatment can improve bone, body composition (how much lean muscle mass an individual has), and quality of life in patients with vitamin D deficiency.
Vitamin D treatment is very safe. Patients with a chronic granuloma-forming disease and some patients with lymphoma who receive vitamin D treatment may get too much calcium in their blood or urine. Careful monitoring of blood vitamin D levels will help check for this possible problem.
How much vitamin D do you need?
In 2010 the Institute of Medicine set new Recommended Daily Allowances, or RDAs, of vitamin D for most children and adults. However, individuals at risk of low vitamin D may need more than the RDA. Therefore, The Endocrine Society guidelines suggest intakes (the amounts of vitamin D an individual should consume) for at-risk people. The table shows both sets of advice and the upper limit (highest intake) thought to be safe.
|Suggested Vitamin D Intake|
(Institute of Medicine Recommendations)
At Risk of Vitamin D Deficiency
(The Endocrine Society Suggestions)
|Age||RDA (IU/day)||Upper Limit (IU/day)||Daily Recommendation (IU/day)||Upper Limit (IU/day)|
|Infants and children|
|Pregnant or breast-feeding|
IU = International Units
Can you get too much vitamin D?
For most people, there is no downside to taking vitamin D supplements. Getting too much vitamin D is uncommon at the recommended intake. An overdose of vitamin D is possible, though, when daily supplements exceed the suggested upper limits. It is therefore important that you take the dose of vitamin D that your doctor recommends.
Excess vitamin D can cause calcium deposits, nausea, vomiting, itching, increased thirst and urination, weakness, and kidney failure.
What can you do to help prevent and treat vitamin D deficiency?
To prevent vitamin D deficiency, make sure you get at least the RDA through supplements and the foods you eat. Foods with natural vitamin D include:
Foods that often have added vitamin D include:
Ask your doctor if you should undergo a vitamin D blood test if you think you are at risk of low vitamin D. Also discuss whether you should increase your daily vitamin D intake.
You can reverse vitamin D deficiency over time by getting enough vitamin D. Take your prescribed dose of vitamin D and keep appointments with your doctor, to ensure the success of your treatment and healthy bones.