What is vitamin D and what does it do?
Vitamin D is a nutrient found in some foods that is needed for health and to
maintain strong bones. It does so by helping the body absorb calcium (one of bone's main building blocks) from food and supplements. People who get too little
vitamin D may develop soft, thin, and brittle bones, a condition known as rickets in children and osteomalacia in
Vitamin D is important to the body in many other ways as well. Muscles need it to
move, for example, nerves need it to carry messages between the brain and every body part, and the immune system
needs vitamin D to fight off invading bacteria and viruses. Together with calcium, vitamin D also helps protect
older adults from osteoporosis. Vitamin D is found in cells throughout the body.
What foods provide vitamin D?
Very few foods naturally have vitamin D. Fortified foods provide most of the vitamin D in American diets.
- Fatty fish such as salmon, tuna, and mackerel are among the best sources.
- Beef liver, cheese, and egg yolks provide small amounts.
- Mushrooms provide some vitamin D. In some mushrooms that are newly available in stores, the vitamin D
content is being boosted by exposing these mushrooms to ultraviolet light.
- Almost all of the U.S. milk supply is fortified with 400 IU of vitamin D per quart. But foods made from
milk, like cheese and ice cream, are usually not fortified.
- Vitamin D is added to many breakfast cereals and to some brands of orange juice, yogurt, margarine, and soy
beverages; check the labels.
Can I get vitamin D from the sun?
The body makes vitamin D when skin is directly exposed to the sun, and most people meet at least some of their
vitamin D needs this way. Skin exposed to sunshine indoors through a window will not produce vitamin D. Cloudy
days, shade, and having dark-colored skin also cut down on the amount of vitamin D the skin makes.
However, despite the importance of the sun to vitamin D synthesis, it is prudent to limit exposure of skin to
sunlight in order to lower the risk for skin cancer. When out in the sun for more than a few minutes, wear
protective clothing and apply sunscreen with an SPF (sun protection factor) of 8 or more. Tanning beds also cause
the skin to make vitamin D, but pose similar risks for skin cancer.
People who avoid the sun or who cover their bodies with sunscreen or clothing should include good sources of
vitamin D in their diets or take a supplement. Recommended intakes of vitamin D are set on the assumption of little
Am I getting enough vitamin D?
Because vitamin D can come from sun, food, and supplements, the best measure of one's vitamin D status is blood
levels of a form known as 25-hydroxyvitamin D. Levels are described in either nanomoles per liter (nmol/L) or
nanograms per milliliter (ng/mL), where 1 nmol/L = 0.4 ng/mL.
In general, levels below 30 ng/mL are too low for bone or overall health, and levels above 100 ng/mL
are probably too high. Levels of 50 ng/mL or above) are recommended for optimal health in
By these measures, a large percentage of Americans are vitamin D deficient and almost no one has
levels that are too high. In general, young people have higher blood levels of 25-hydroxyvitamin D than older
people and males have higher levels than females. By race, non-Hispanic blacks tend to have the lowest levels and
non-Hispanic whites the highest. The majority of Americans have blood levels lower than 30 ng/mL.
Certain other groups may not get enough vitamin D:
- Breastfed infants, since human milk is a poor source of the nutrient. Breastfed infants should be given a
supplement of 400 IU of vitamin D each day.
- Older adults, since their skin doesn't make vitamin D when exposed to sunlight as efficiently as when they
were young, and their kidneys are less able to convert vitamin D to its active form.
- People with dark skin, because their skin has less ability to produce vitamin D from the sun.
- People with disorders such as Crohn's disease or celiac disease who don't handle fat properly, because
vitamin D needs fat to be absorbed.
- Obese people, because their body fat binds to some vitamin D and prevents it from getting into the
It is for the reasons described above that the majority of Americans,especially those in the
northern hemisphere should be supplementing their diets with vitamin D3.
Can vitamin D be harmful?
Yes, when amounts in the blood become too high. Signs of toxicity include nausea, vomiting, poor appetite,
constipation, weakness, and weight loss. And by raising blood levels of calcium, too much vitamin D can cause
confusion, disorientation, and problems with heart rhythm. Excess vitamin D can also damage the kidneys.
Vitamin D toxicity almost always occurs from overuse of supplements. Most instances of toxicity occurred when
100000 iu's/day were taken for more than a few weeks. Excessive sun exposure doesn't cause vitamin D poisoning
because the body limits the amount of this vitamin it produces.
Are there any interactions with vitamin D that I should know about?
Like most dietary supplements, vitamin D may interact or interfere with other medicines or supplements you might
be taking. Here are several examples:
- Prednisone and other corticosteroid medicines to reduce inflammation impair how the body handles vitamin D,
which leads to lower calcium absorption and loss of bone over time.
- Both the weight-loss drug orlistat (brand names Xenical® and Alli®) and the cholesterol-lowering drug
cholestyramine (brand names Questran®, LoCholest®, and Prevalite®) can reduce the absorption of vitamin D and
other fat-soluble vitamins (A, E, and K).
- Both phenobarbital and phenytoin (brand name Dilantin®), used to prevent and control epileptic seizures,
increase the breakdown of vitamin D and reduce calcium absorption.
Tell your doctor, pharmacist, and other health care providers about any dietary supplements and medicines you
What are some effects of vitamin D on health?
Vitamin D is being studied for its possible connections to several diseases and medical problems, including
diabetes, hypertension, and autoimmune conditions such as multiple sclerosis. In addition, bone disorders and some
types of cancer may result from low levels of vitamin D.
Information from this page was compiled mostly from http://ods.od.nih.gov/factsheets/VitaminD-Consumer/
HOW MUCH VITAMIN D3 SHOULD I TAKE?
Most nutritionally conscious physicians recommend 3500-5000 iu/day for adults and roughly half this amount for
kids per day along with a meal. In addition, when supplementing with Vitamin D3 that you also take Vitamin K2.
There are three different vitamin K molecules. Vitamin K2, menaquinones, are produced naturally by bacteria unlike
its more popular cousin, vitamin K1, which is found in greater concentrations in green leafy vegetables. Numerous
studies have shown that vitamin K2 is the more bioavailable form of the nutrient, and more powerfully influences
bone building than K1. There are two forms of vitamin K2 commonly used in supplements, synthetic MK-4, and natural
MK-7 (extracted from the traditional Japanese food, Natto). The MK-7 form has been shown to have 6 times the
activity of MK-4 in the blood. MK-7 has also been found to remain in the blood approximately nine times as long as
the MK-4 (8 hours versus 72 hours), making it the optimal form of K2 for health.
Caution:If you’re taking blood thinning medicines, such as Warfarin or Coumadin, don’t
take vitamin K supplements. This is because it may affect how well your blood clots.
New studies reveal RDA for Vitamin D3 is way too low, maybe by a factor of 10: http://www.mdpi.com/2072-6643/6/10/4472/htm