What is vitamin D?
Vitamin D is a fat soluble vitamin that your body needs to absorb calcium.
It also plays an important role in maintaining muscle strength. Vitamin
D deficiency is associated with reduced calcium absorption, bone loss,
reduced muscle strength, and increased risk of fractures.
How much vitamin D do I need?
The American Academy of Pediatrics recommends 400 IU of vitamin D each day for infants from birth to 12 months of age. Vitamin D is found in formula or given as prescription drops (necessary for all breast-fed infants. The Institute of Medicine recommends 600 IU of vitamin D for most people from age 1 to 70 years old and 800 IU for people age 71 years and older. These are general recommendations for the healthy population. Some people need more vitamin D. Your healthcare provider may tell you that you need more vitamin D if you have osteoporosis or other chronic medical conditions and have been diagnosed with low vitamin D levels.
What populations are at higher risk for vitamin D deficiency?
Some of the populations at higher risk for vitamin D
deficiency than the general population include:
- Infants fed only breastmilk
- Older individuals who consume diets low in vitamin D and
do not take supplements containing vitamin D
- Individuals who take total sun precautions, consume diets low in
vitamin D and do not take a supplement containing vitamin D
- Homebound individuals who get little sun exposure, consume diets
low in vitamin D and do not take a supplement containing vitamin
- Individuals with malabsorption syndromes who are not able to absorb
dietary vitamin D (examples include: some people with Crohn's disease
or celiac disease)
- Individuals with liver or kidney diseases who may be less able
to process vitamin D
- Individuals taking certain medications that interfere with
vitamin D metabolism (Some of these medications include steroids
taken for more than 3 months, certain medications used to control
seizures such as dilantin or phenobarbitol and cholestryamine
used to lower the cholesterol level)
- Obese individuals
What should I do if I am at high risk for vitamin D deficiency?
It is important to speak
to your doctor or healthcare provider about vitamin D and your bone health. If you have risk factors for vitamin D deficiency, it does
not mean that you actually have vitamin D deficiency. Only your doctor
or healthcare provider can make that determination. If your doctor or health care provider feels that it is necessary, he or she will recommend a
blood test called 25(OH) D to check your vitamin D level.
What are the sources of vitamin D?
Sun exposure is not a reliable way to get vitamin D and there is concern about harmful ultraviolet rays that can put an individual at risk for skin cancer, cataracts, and premature aging. Vitamin D from food
and dietary supplements offer the same health benefits as vitamin D from the
sun- without the danger of sun exposure.
To get enough vitamin D, most people need supplements. Vitamin D rich foods tend to be high in fat and not eaten daily as part if the typical US diet. These include fatty fish and fish oils. Some foods are fortified with vitamin D, meaning that although they do not naturally contain vitamin D, the vitamin is added to the food or beverage.
There is limited but growing information about the vitamin D content of foods. Vitamin D content of foods is stated in international
units (IU). The amount of vitamin D that is found in food varies depending on the
feed given to animal sources of vitamin D, the brand purchased, as well
as the amount of vitamin D added to fortified foods. For example, milk
is fortified with 100 IU of vitamin D per 8-ounce cup. Most dairy products
including yogurts and cheeses have not traditionally been made with fortified
milk. However, recently a few dairy products and other foods have
been manufactured with vitamin D added. It is important to read
food labels for vitamin D content.
What is the difference between vitamin D3 and vitamin D2
The type of vitamin D added to fortified
foods varies. Vitamin D3 (cholecalciferol) is found in animal products or made from the ultraviolet irradiation
of lanolin. Vitamin D2 is more common in vegetarian food sources and
manufactured through the ultraviolet irradiation of yeast. Foods fortified
with vitamin D3 include cow's milk, some yogurts, vitamin D fortified
orange juice, some breakfast cereals and some breakfast bars.
Vitamin D3 and Vitamin D2 can also be obtained from multivitamins, in combination with some calcium supplements, or alone as a separate
vitamin D supplement.
The nutrition fact labels
of supplements can be useful to find out the type of vitamin D added. Individuals who follow vegan diets (strict vegetarian
diets that exclude all animal products and by-products) will prefer the vegetarian source of vitamin D, vitamin D2. The most recent evaluation of scientific studies indicates that vitamin D2 and vitamin D3 are both used efficiently by most healthy people.
It's sensible to avoid sources of vitamin D that are high in retinol.
Vitamin D and vitamin
A are both fat-soluble vitamins that may be present in some
of the same foods or supplements. Cod liver oil, for example, contains
high amounts of both vitamin D and a type of vitamin A called
A large study found that postmenopausal women who consumed very
high intakes of retinol (from food sources such as cod liver oil and liver,
from certain multivitamins, or from vitamin A supplements) appeared
to have an increased risk of hip fractures. However, there was
no association between high intakes of another type of vitamin A, called
beta-carotene and the risk of hip fracture. Beta-carotene is found
in a wide variety of yellow and orange-colored fruits and vegetables,
as well as green leafy vegetables.
A large population study also found an association between high
intakes of retinol from supplements and hip fracture but reported no
association between retinol from cod liver oil or other food sources
and fracture risk. Although further investigation is needed to
study the relationship between retinol from various sources and fracture
risk, it is sensible to avoid foods and supplemental sources of vitamin
D that are high in retinol. Until more information is available, this includes the avoidance of cod
liver oil and vitamin D supplements that have vitamin A added.