Vitamin D & Vitamin D Deficiency
What is vitamin D and why is it needed?
Vitamin D is one of many nutrients our bodies need to stay healthy. Among the vitamin's main functions, it helps the body:
- Absorb calcium. Vitamin D, along with calcium, helps build bones and keep bones strong and healthy.
- Block the release of parathyroid hormone. This hormone reabsorbs bone tissue, which makes bones thin and brittle.
Vitamin D may also play a role in muscle function and the immune system. The immune system is your body's defense system. It helps protect it against infections and other illnesses. Taking vitamin D every day has been shown to reduce the risk of falling in older individuals.
Other ways vitamin D is thought to help us, and how much we would need to take, is an area of active research (and controversy). There have been studies to suggest that it might help prevent colon, prostate, and breast cancers. There is also some research that it might help prevent and treat diabetes, heart disease, high blood pressure, and multiple sclerosis. However, the results of many of these studies are either preliminary or under debate. Without other long-term research, even many of the researchers who conducted these initial studies are cautious about recommending vitamin D for the prevention of these diseases.
What are the sources of vitamin D?
You can get vitamin D through sun exposure, your diet, and supplements.
Vitamin D is produced when your skin is exposed to sunshine. The amount of vitamin D that your skin makes depends on such factors as the season (i.e., there's usually less sunshine in winter months), the time of day (the sun's rays are most powerful between 10 am and 3 pm), the amount of cloud cover and air pollution, and where you live (cities near the equator have higher UV levels). It's the UV (ultraviolet) light in sunlight that causes your skin to make vitamin D.
Food sources (diet)
The best way to get enough vitamin D every day is to eat a variety of healthy foods from all food groups. The vitamin content of various foods is shown in the table.
Vitamin D Content of Various Foods
International Units per serving
- Cod liver oil, 1 tablespoon: 1360
- Swordfish, cooked, 3 ounces: 566
- Salmon (sockeye) cooked, 3 ounces: 477
- Tuna, canned in water, drained, 3 ounces: 154
- Orange juice fortified with vitamin D, 1 cup: 137
- Milk, vitamin fortified, 1 cup: 115-124
- Yogurt, fortified with 20% of the daily value of vitamin D, 6 ounces: 80
- Margarine, fortified, 1 tablespoon: 60
- Sardines, canned in oil, drained, 2 sardines: 46
- Liver, beef, cooked, 3 ounces: 42
- Egg yolk, 1 large: 41
- Cereal, fortified with 10% of the daily value of vitamin D, 1 cup: 40
- Cheese, Swiss, 1 ounce: 6
Source: Vitamin D. Health Professionals. Dietary Supplement Fact Sheet. National Institutes of Health. Office of Dietary Supplements. June 24, 2011
It is important to check product labels, as the amount of added vitamin D varies when it is artificially added to products such as orange juice, yogurt, and margarine.
Since there is a limited number of foods that contain vitamin D, getting enough vitamin D from your diet alone is difficult. While sun exposure does produce vitamin D, too much sun exposure can increase the risk of skin cancer. Therefore, the addition of vitamin D supplements may be needed.
How much vitamin D is needed?
In healthy people, the amount of vitamin D needed per day is shown in the chart (according to the Institute of Medicine). It is important to know that these are general recommendations. If your doctor is checking your blood levels, he or she might recommend higher or lower doses based on your individual needs.
According to the American Academy of Clinical Endocrinologists, it may be appropriate to do a blood test of vitamin D in many patients with osteoporosis. The amount of vitamin D supplement can be customized for each person, based on the results. For many older patients, a vitamin D supplement containing anywhere between 800 to 2000 IU daily, which can be obtained without a prescription, can be both safe and beneficial. It is important to speak with your doctor about your individual needs.
Daily Recommended Vitamin D Intake
Infants 0 - 6 months
Recommended Dietary Allowance (IU/day): 400 Upper Level Intake (IU/day): 1,000
Infants 6 - 12 months
Recommended Dietary Allowance (IU/day): 400 Upper Level Intake (IU/day): 1,500
1 - 3 years old
Recommended Dietary Allowance (IU/day): 600 Upper Level Intake (IU/day): 2,500
4 - 8 years old
Recommended Dietary Allowance (IU/day): 600 Upper Level Intake (IU/day): 3,000
9 - 70 years old
Recommended Dietary Allowance (IU/day): 600 Upper Level Intake (IU/day): 4,000
Over 70 years old
Recommended Dietary Allowance (IU/day): 800 Upper Level Intake (IU/day): 4,000
14 - 50 years old, pregnant/lactating
Recommended Dietary Allowance (IU/day): 600 Upper Level Intake (IU/day): 4,000
Source: Institute of Medicine, released 11/30/2010
Are there medical conditions that can cause a vitamin D deficiency (shortage)?
Yes. Vitamin D deficiency can be caused by specific medical conditions, such as:
- Kidney and liver diseases. These diseases reduce the amount of an enzyme needed to change vitamin D to a form that is used in the body. Lack of this enzyme leads to an inadequate level of vitamin D in the body.
- Cystic fibrosis, Crohn's disease, and celiac disease. These diseases do not allow the intestines to absorb enough vitamin D.
- Gastric bypass surgery. This weight-loss surgery removes part of the stomach and/or the intestines. Reducing the size of these organs lowers the amount of vitamin D-containing nutrients that can be absorbed.
- Obesity. A body mass index greater than 30 is associated with lower vitamin D levels. It is thought that the fat actually holds onto the vitamin D, and does not allow it to be released into the bloodstream.
Other factors that can lead to vitamin D deficiency:
- Age. The skin's ability to make vitamin D lessens with age.
- Mobility. People who are homebound or are rarely outside (e.g., in nursing homes and other facilities) are not able to use sun exposure as a source of vitamin D.
- Skin color. Dark-colored skin is less able to make vitamin D than fair-colored skin.
- Human breast milk. A woman's breast milk only contains a small amount of vitamin D. Infant formulas often do, too. Therefore infants, particularly those who are breastfed exclusively, are at risk for not receiving enough vitamin D.
Are there medications that can cause a vitamin D deficiency?
Yes. Vitamin D levels can be lowered by certain medications. These include: laxatives, steroids (e.g., prednisone), cholesterol-lowering drugs (e.g., cholestyramine and colestipol), seizure-control drugs (e.g., phenobarbital and phenytoin), a tuberculosis drug (rifampin), and a weight-loss drug (orlistat).
Always tell your doctor about the drugs you take and any vitamin D supplements or other supplements or herbs/alternative health products that you take.
How often do I need to get my vitamin D level checked?
Routine checks of vitamin D levels are not currently recommended. However, your doctor might need to check your levels if you have medical conditions, risk factors for vitamin D deficiency, or are taking certain medications, as already discussed. Sometimes vitamin D levels can be checked as a cause of symptoms such as long-lasting body aches and a history of falls, or bone fractures without significant trauma.
What health problems can occur if a person doesn't get enough vitamin D?
Severely low levels of vitamin D can result in a disease called osteomalacia in adults, and rickets in children. If left untreated, both conditions lead to soft, brittle bones, bone pain, and muscle pain and weakness. Osteoporosis is associated with reduced bone density, which leads to an increased risk of falls and bone fractures.
Can a person ever have too much vitamin D?
Yes. See the table, "Daily Recommended Vitamin D Intake." This table lists the upper limits for vitamin D levels by age.
Symptoms of too much vitamin D include:
- increased thirst and urination
- poor appetite
- weight loss
- heart rhythm problems
- kidney damage
- pancreatic cancer (possibly).
Do not take higher-than-recommended doses of vitamin D without first discussing it with your doctor. However, your doctor might recommend higher doses of vitamin D if he or she is checking your blood levels and adjusting your dose accordingly.
How is vitamin D deficiency treated and how can it be prevented?
The goals of treatment and prevention are the same -- to reach, and then maintain, an adequate level of vitamin D in the body. A combination of methods is used to do this, including:
Eating more foods that contain vitamin D. See vitamin D food sources table included in this article. Keep in mind that foods alone usually don't meet the daily recommended levels of vitamin D.
Getting some exposure to sunshine -- but not TOO much. Exactly how much sun exposure is needed is not clear. Five to 15 minutes of sun exposure two to three times a week to the face, arms, legs, or back may be all that is needed to absorb a suitable amount of vitamin D. Older patients, those with darker skin color, and those living in northern climates might need more sun exposure (especially in early spring and late fall). The use of sunscreen, and standing behind a window, prevents vitamin D from being produced in the skin.
However, know that too much sunshine increases the risk of skin cancer and ages the skin. The American Academy of Dermatology advises that when in the sun, use a sunscreen with an SPF of at least 30.
Using vitamin D supplements. Vitamin D comes in two forms: D2 (ergocalciferol) and D3 (cholecalciferol). Studies have shown that these two forms are equally good for bone health. Work with your doctor to determine if you need to take a vitamin supplement and, if so, how much to take. It is important to discuss how much vitamin D you are taking with your doctor, especially if you are taking more than what is listed in the chart above. Though higher doses are often safely used, too much vitamin D can build up in the body if used incorrectly.