Vitamin D is a fat-soluble vitamin that the body produces when the skin gets exposed to sunlight. To use it, the body needs to convert it to an active form called hydroxyvitamin D [25 OH D] or calcidiol. The results of a serum vitamin D blood test may show the following:. Vitamin D has many important functions, including :. Some experts have suggested that vitamin D may help prevent type 2 diabetes.
However, in a study , 2, people at risk of type 2 diabetes took either a vitamin D supplement of 4, international units IU a day or a placebo. Vitamin D levels increased in those who took the supplement. However, taking the supplement did not appear to reduce the risk of diabetes developing.
Learn more about the health benefits of vitamin D. Diet : People who do not eat enough vitamin D-rich foods, including fortified dairy products and cereals, may have low levels of vitamin D. Lifestyle factors : Some people spend little time outdoors due to work, ill health, a lack of outdoor space in their neighborhood, or other factors.
These people have less opportunity to expose their skin to sunlight. Those who wear clothes that cover all of their body, whether to protect it from the sun or for cultural or religious reasons, may also have a higher risk of a deficiency. The Office of Dietary Supplements ODS recommend that people who use a lot of sunscreen or wear clothing that covers the body should include sources of vitamin D in their diet.
People who live in a hot climate may also be at risk, as they often try to avoid the heat and strong sunlight by staying indoors. Pollution : Particles in the air can block UVB rays and prevent them from reaching the skin. People who live in highly polluted areas may also be more likely to avoid spending time outside. These include steroids and some drugs for lowering cholesterol , among others.
Smoking : Levels of deficiency appear to be higher among smokers. Some experts have suggested that smoking may affect the gene that activates the production of vitamin D-3 in the body.
Obesity : Research has found lower vitamin D levels in people with obesity , or a body mass index BMI of 30 or more. This link may be stem from the ways in which body fat affects vitamin D absorption.
Some people with obesity may spend less time outdoors due to mobility issues. Those who have undergone bariatric surgery may also have absorption problems. Conversely, people whose BMI of 25— The authors suggest that dietary factors are responsible for this difference. Skin type : People with darker skin need more sunlight exposure to produce vitamin D than those with lighter skin.
People with pale skin or a history of skin cancer may avoid sun exposure to protect their skin from damage. Age : The ability to convert vitamin D to calcitriol may decline with age due to decreased kidney function. As a result, calcium absorption will fall.
Kidney and liver health : People with liver disease and kidney disease tend to have lower vitamin D levels. Pregnancy : The need for vitamin D may increase during pregnancy, but experts remain unsure whether supplements are a good idea. The authors of a Cochrane review concluded that taking supplements during pregnancy may reduce the risk of preeclampsia , gestational diabetes, low birth weight, and severe bleeding after delivery.
High levels of blood calcium hypercalcemia can cause confusion, disorientation, and problems with heart rhythm. Most cases of vitamin D toxicity happen when someone overuses vitamin D supplements.
Excessive sun exposure doesn't cause vitamin D poisoning because the body limits the amount of this vitamin it produces. The information on this site should not be used as a substitute for professional medical care or advice.
Contact a health care provider if you have questions about your health. What is vitamin D deficiency? Vitamin D deficiency means that you are not getting enough vitamin D to stay healthy. Why do I need vitamin D and how do I get it? How much vitamin D do I need? What causes vitamin D deficiency? You can become deficient in vitamin D for different reasons: You don't get enough vitamin D in your diet You don't absorb enough vitamin D from food a malabsorption problem You don't get enough exposure to sunlight.
Your liver or kidneys cannot convert vitamin D to its active form in the body. You take medicines that interfere with your body's ability to convert or absorb vitamin D Who is at risk of vitamin D deficiency?
Some people are at higher risk of vitamin D deficiency: Breastfed infants, because human milk is a poor source of vitamin D. If you are breastfeeding , give your infant a supplement of IU of vitamin D every day.
Older adults, because your skin doesn't make vitamin D when exposed to sunlight as efficiently as when you were young, and your kidneys are less able to convert vitamin D to its active form. People with dark skin, which 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.
People who have obesity , because their body fat binds to some vitamin D and prevents it from getting into the blood. People who have had gastric bypass surgery People with osteoporosis People with chronic kidney or liver disease. People with hyperparathyroidism too much of a hormone that controls the body's calcium level People with sarcoidosis , tuberculosis , histoplasmosis , or other granulomatous disease disease with granulomas, collections of cells caused by chronic inflammation People with some lymphomas , a type of cancer.
In a large observational study in more than 1, middle-age menopausal or postmenopausal women, researchers found a strong link between low vitamin D levels and low bone mineral density However, a controlled study found that women who were deficient in vitamin D experienced no improvement in bone mineral density when they took high-dose supplements, even if their blood levels improved Regardless of these findings, getting adequate vitamin D intake and maintaining blood levels within the optimal range may be a good strategy for protecting your bone mass and reducing your fracture risk.
A diagnosis of low bone mineral density may be a sign of vitamin D deficiency. Getting enough of this vitamin is important for preserving bone mass as you get older. Hair loss is often attributed to stress , which is certainly a common cause. However, when hair loss is severe, it may be the result of a disease or nutrient deficiency. Hair loss in women has been linked to low vitamin D levels, though there is very little research on this to date In particular, research suggests that low vitamin D levels are linked to alopecia areata and may be a risk factor for developing the disease 33 , Alopecia areata is an autoimmune disease characterized by severe hair loss from the head and other parts of the body.
One study among people with alopecia areata showed that lower vitamin D blood levels tended to be associated with more severe hair loss In another study, applying a synthetic form of the vitamin topically for 12 weeks was found to significantly increase hair regrowth in 48 people with alopecia areata Many other foods and nutrients may affect the health of your hair.
If you experience hair loss, you may be interested in the 14 best foods for hair growth. Hair loss may be a sign of vitamin D deficiency in female pattern hair loss or the autoimmune condition alopecia areata. A few studies have found that taking high-dose vitamin D supplements may reduce various types of pain in people who are deficient 42 , It may have to do with the interaction between the vitamin and pain-sensing nerve cells.
Obesity is one risk factor for vitamin D deficiency One longitudinal study including men and women found a possible link between low vitamin D status and both abdominal fat and increased weight. However, this study found that such effects were more prominent in men Another review confirms that while vitamin D deficiency may be seen in cases of obesity, further studies are needed to determine whether vitamin D could help prevent weight gain According to one review, levels of calcidiol, a form of vitamin D, was found to be lower in people with anxiety, as well as those with depression A separate study in pregnant women found that vitamin D levels could help reduce anxiety, improve sleep quality, and possibly help prevent postpartum depression Treatment for vitamin D deficiency primarily consists of supplementation.
If your doctor determines that you are indeed lacking this nutrient, they may recommend the following options. A vitamin D deficiency may be treated with vitamin D supplementation. You may find these easily over the counter, but you should ask your doctor for specific recommendations to ensure the right dosage.
These come in much stronger doses of up to 50, IU Another potential option your doctor may consider is vitamin D injections Aside from vitamin D supplementation, your doctor may recommend adding more vitamin-D-rich foods to your daily diet. Options may include 52 :. Since sunlight is also a natural source of vitamin D, your doctor may recommend going outside more often.
People who live near the equator and get frequent sun exposure are less likely to be deficient, as their skin produces enough vitamin D. As a rule of thumb, you may consider asking your doctor to check for vitamin D deficiency if you notice any possible symptoms and have any risk factors.
They can check your vitamin D levels with a blood test. You can either increase your sun exposure or add more vitamin-D-rich foods to your diet, such as fatty fish or fortified dairy products.
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