Vitamins are substances that your body needs to grow and develop normally. Vitamin D helps your body absorb calcium. Calcium is one of the main building blocks of bone. A lack of vitamin D can lead to bone diseases such as osteoporosis or rickets. Vitamin D also has a role in your nerve, muscle, and immune systems.

You can get vitamin D in three ways: through your skin, from your diet, and from supplements. Your body forms vitamin D naturally after exposure to sunlight. However, too much sun exposure can lead to skin aging and skin cancer. So many people try to get their vitamin D from other sources.

Vitamin D-rich foods include egg yolks, saltwater fish, and liver. Some other foods, like milk and cereal, often have added vitamin D.

You can also take vitamin D supplements. Check with your health care provider to see how much you should take. People who might need extra vitamin D include

• Seniors
• Breastfed infants
• People with dark skin
• People with certain conditions, such as liver diseases, cystic fibrosis and Crohn's disease
• People who have obesity or have had gastric bypass surgery

It has long been known that vitamin D is necessary for strong bones and teeth, but its health benefits also include lower risks for heart disease, diabetes, rheumatoid arthritis and multiple sclerosis. These effects involve its essential roles in calcium absorption, bone metabolism and the expression of many genes-and most people don't get enough of this important vitamin.

Vitamin D is different from most other vitamins in that it can be made by the action of sunlight on the skin, hence, its name as the "sunshine vitamin". In order to make enough vitamin D, one must get sufficient sun exposure directly on the skin. In North Dakota, this means the middle of the day and only in the summer months. A study at the USDA Grand Forks Human Nutrition Center showed that, even in midsummer, the solar exposure is sufficient to produce significant amounts of vitamin D only between the hours of 10 am and 4 pm. Even then, our indoor lifestyles, as well as the use of long sleeved clothing and sunscreens, effectively limit our capacity to make vitamin D. Accordingly, people living north of Atlanta, Georgia show seasonal variations in their blood vitamin D levels, with the highest levels in the summer and lower levels through the rest of the year. The difference in vitamin D levels mean that most people don't have sufficient levels of vitamin D in their bodies they need throughout the year. So, no matter where people live, most need extra sources of vitamin D to assure adequate amounts to meet their daily needs.

Very few foods in nature contain vitamin D, but some are "fortified" with the vitamin. The amount of vitamin D that can be added in fortified American foods is regulated by the U.S. Food and Drug Administration. For example, milk actually contains very little vitamin D, but is usually supplemented with vitamin D3 for U.S. retail sales. In addition to milk, important sources of vitamin D include certain types of yogurt and fruit juices, fortified cereals and breakfast bars. In order to know how much vitamin D is in your food, read the nutritional label. It will tell you how much vitamin D you are getting in that food. Many people also choose over-the-counter dietary supplements containing vitamin D.

The biggest question most people have is, "How much vitamin D should I take?" Most people aged 1 to 70 years, are recommended to consume 600 international units (IU) of vitamin D per day. For people over 70 years, 800 IU per day is recommended that's because the ability to produce vitamin D in skin declines with age. For infants in the first year of life, the recommendation is a daily intake of 400 IU. Intakes up to 4000 IU per day are regarded as safe for children and adults aged 9 to 70 years.

Vitamin D is especially important during pregnancy, as the mother must meet her own needs for vitamin D as well as those of her developing baby and the placenta which provides oxygen and other nutrients to the growing baby. Insufficient vitamin D impairs the development of the placenta and its blood vessels. That can present a nutritional challenge for the baby an increase the mother's risk of preeclampsia, a form of high blood pressure in pregnancy. Preeclampsia is a serious pregnancy related complication, which can cause babies to be born small and increase the risk of future development of high blood pressure in both the mother and child.

Adequate vitamin D also is especially important for breastfeeding mothers. The vitamin D content of breast milk reflects the vitamin D status of the mother. If a mother's breast milk has inadequate vitamin D she may not provide sufficient amounts to meet her infant's needs. Vitamin D is important to overall health and wellness no matter how old you are. Be sure to get enough, so you can get the benefits of this "D"-lightful vitamin.

Vitamin D is a nutrient you need for good health. It helps your body absorb calcium, one of the main building blocks for strong bones. Together with calcium, vitamin D helps protect you from developing osteoporosis, a disease that thins and weakens the bones and makes them more likely to break. Your body needs vitamin D for other functions too. Your muscles need it to move, and your nerves need it to carry messages between your brain and your body. Your immune system needs vitamin D to fight off invading bacteria and viruses.

The amount of vitamin D you need each day depends on your age. Average daily recommended amounts are listed below in micrograms (mcg) and International Units (IU):

Very few foods naturally contain vitamin D. Fortified foods provide most of the vitamin D in the diets of people in the United States. Check the Nutrition Facts label for the amount of vitamin D in a food or beverage.

• Almost all of the U.S. milk supply is fortified with about 3 mcg (120 IU) vitamin D per cup. Many plant-based alternatives such as soy milk, almond milk, and oat milk are similarly fortified. 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 other food products.
• Fatty fish (like trout, salmon, tuna, and mackerel) and fish liver oils are among the best natural sources of vitamin D.
• Beef liver, cheese, and egg yolks have small amounts of vitamin D.
• Mushrooms provide a little vitamin D. Some mushrooms have been exposed to ultraviolet light to increase their vitamin D content.

Vitamin D is a fat-soluble vitamin that is essential for human health. It comes in many forms. The two major forms are vitamin D₂ and vitamin D₃. Vitamin D without a subscript represents either vitamin D₂ or vitamin D₃ or both. The major function of vitamin D is to help with the absorption of calcium and phosphorus in the small intestine. Vitamin D deficiency can lead to abnormalities in bone metabolism, such as rickets in children or osteomalacia in adults. Excess intake of vitamin D can also be harmful, elevating calcium levels in the blood (hypercalcemia). Vitamin D is a food additive added to food as an optional ingredient.

Under the law, the FDA may approve the use of a food additive only after conducting a scientific safety review of the information provided in the petition to ensure that use of ingredients added to foods are safe for the general population. In this case, the FDA evaluated the projected human dietary exposure to vitamin D from foods and dietary supplements, safety data, and other relevant information and found these uses of vitamin D to be safe.

In July 2016, FDA approved an increase to the amount of vitamin D that may be added as an optional ingredient to milk, and approved the addition of vitamin D to beverages made from edible plants intended as milk alternatives, such as beverages made from soy, almond, and coconut, and edible plant-based yogurt alternatives. Vitamin D was already authorized for use in soy beverages, but today’s approval increases the authorized amount for such beverages that are intended as milk alternatives.

The approval, which amends existing food additive regulations, will allow manufacturers to voluntarily add up to 84 IU/100g of vitamin D3 to milk, 84 IU/100g of vitamin D2 to plant-based beverages intended as milk alternatives, and 89 IU/100g of vitamin D2 to plant-based yogurt alternatives.

Your body makes vitamin D when your bare skin is exposed to the sun. Most people get at least some vitamin D this way. However, clouds, smog, old age, and having dark-colored skin reduce the amount of vitamin D your skin makes. Also, your skin does not make vitamin D from sunlight through a window.

Ultraviolet radiation from sunshine can cause skin cancer, so it’s important to limit how much time you spend in the sun. Although sunscreen limits vitamin D production, health experts recommend using sunscreen with a sun protection factor (SPF) of 15 or more when you’re out in the sun for more than a few minutes.

The epidermal layer of human skin synthesizes vitamin D when exposed to UV radiation. In the presence of sunlight, a form of vitamin D3 called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The liver converts cholecalciferol to calcidiol, which is then converted to calcitriol (the active chemical form of the vitamin) in the kidneys. Vitamin D is essential for normal absorption of calcium and phosphorous, which are required for healthy bones. The absence of sun exposure can lead to a lack of vitamin D in the body, leading to a condition called rickets, a painful condition in children where the bones are misshapen due to a lack of calcium, causing bowleggedness. Elderly individuals who suffer from vitamin D deficiency can develop a condition called osteomalacia, a softening of the bones. In present day society, vitamin D is added as a supplement to many foods, including milk and orange juice, compensating for the need for sun exposure.

In addition to its essential role in bone health, vitamin D is essential for general immunity against bacterial, viral, and fungal infections. Recent studies are also finding a link between insufficient vitamin D and cancer.

Vitamin D is found in multivitamin/multimineral supplements. It is also available in dietary supplements containing only vitamin D or vitamin D combined with a few other nutrients. The two forms of vitamin D in supplements are D2 (ergocalciferol) and D3 (cholecalciferol). Both forms increase vitamin D in your blood, but D3 might raise it higher and for longer than D2. Because vitamin D is fat-soluble, it is best absorbed when taken with a meal or snack that includes some fat.

• Levels of 50 nmol/L (20 ng/mL) or above are adequate for most people for bone and overall health.
• Levels below 30 nmol/L (12 ng/mL) are too low and might weaken your bones and affect your health.
• Levels above 125 nmol/L (50 ng/mL) are too high and might cause health problems.

In the United States, most people have adequate blood levels of vitamin D. However, almost one out of four people have vitamin D blood levels that are too low or inadequate for bone and overall health.

Some people are more likely than others to have trouble getting enough vitamin D:

• Breastfed infants. Breast milk alone does not provide infants with an adequate amount of vitamin D. Breastfed infants should be given a supplement of 10 mcg (400 IU) of vitamin D each day.
• Older adults. As you age, your skin's ability to make vitamin D when exposed to sunlight declines.
• People who seldom expose their skin to sunshine because they do not go outside or because they keep their body and head covered. Sunscreen also limits the amount of vitamin D your skin produces.
• People with dark skin. The darker your skin, the less vitamin D you make from sunlight exposure.
• People with conditions that limit fat absorption, such as Crohn’s disease, celiac disease, or ulcerative colitis. This is because the vitamin D you consume is absorbed in the gut along with fat, so if your body has trouble absorbing fat, it will also have trouble absorbing vitamin D.
• People who are obese or have undergone gastric bypass surgery. They may need more vitamin D than other people.

In children, vitamin D deficiency causes rickets, a disease in which the bones become soft, weak, deformed, and painful. In teens and adults, vitamin D deficiency causes osteomalacia, a disorder that causes bone pain and muscle weakness.

It depends. You need vitamin D for strong, healthy bones and to help prevent osteoporosis. Researchers are also studying vitamin D to see if it affects your risk of getting diseases such as diabetes and cancer, but they still don’t fully understand all of its effects in the body.

A scientific committee recently issued new recommended intakes for vitamin D. Most children and adults should get 600 International Units (IUs) a day, while those age 70 and older need 800 IUs.

It’s always best to get nutrients from food first, if you can, before taking supplements. Good sources of vitamin D include tuna and fortified milk. Our bodies also make vitamin D when our skin is exposed to the sun. Knowing exactly how much vitamin D you’re getting can be difficult. Your health care provider can help you determine whether you might need a vitamin D supplement based on such factors as the foods you eat, your skin type, and the amount of sun you’re exposed to. Your health care provider can also test your vitamin D blood levels.

Scientists are studying vitamin D to better understand how it affects health. Here are several examples of what this research has shown:

Bone health and osteoporosis

Long-term shortages of vitamin D and calcium cause your bones to become fragile and break more easily. This condition is called osteoporosis. Millions of older women and men have osteoporosis or are at risk of developing this condition. Muscles are also important for healthy bones because they help maintain balance and prevent falls. A shortage of vitamin D may lead to weak, painful muscles.

Getting recommended amounts of vitamin D and calcium from foods (and supplements, if needed) will help maintain healthy bones and prevent osteoporosis. Taking vitamin D and calcium supplements slightly increases bone strength in older adults, but it’s not clear whether they reduce the risk of falling or breaking a bone.

Cancer

Vitamin D does not seem to reduce the risk of developing cancer of the breast, colon, rectum, or lung. It is not clear whether vitamin D affects the risk of prostate cancer or chance of surviving this cancer. Very high blood levels of vitamin D may even increase the risk of pancreatic cancer.

Clinical trials suggest that while vitamin D supplements (with or without calcium) may not affect your risk of getting cancer, they might slightly reduce your risk of dying from this disease. More research is needed to better understand the role that vitamin D plays in cancer prevention and cancer-related death.

Heart disease

Vitamin D is important for a healthy heart and blood vessels and for normal blood pressure. Some studies show that vitamin D supplements might help reduce blood cholesterol levels and high blood pressure—two of the main risk factors for heart disease. Other studies show no benefits. If you are overweight or obese, taking vitamin D at doses above 20 mcg (800 IU) per day plus calcium might actually raise your blood pressure. Overall, clinical trials find that vitamin D supplements do not reduce the risk of developing heart disease or dying from it, even if you have low blood levels of the vitamin.

Depression

Vitamin D is needed for your brain to function properly. Some studies have found links between low blood levels of vitamin D and an increased risk of depression. However, clinical trials show that taking vitamin D supplements does not prevent or ease symptoms of depression.

Multiple sclerosis

People who live near the equator have more sun exposure and higher vitamin D levels. They also rarely develop multiple sclerosis (MS), a disease that affects the nerves that carry messages from the brain to the rest of the body. Many studies find a link between low blood vitamin D levels and the risk of developing MS. However, scientists have not actually studied whether vitamin D supplements can prevent MS. In people who have MS, clinical trials show that taking vitamin D supplements does not keep symptoms from getting worse or coming back.

Type 2 diabetes

Vitamin D helps your body regulate blood sugar levels. However, clinical trials in people with and without diabetes show that supplemental vitamin D does not improve blood sugar levels, insulin resistance, or hemoglobin A1c levels (the average level of blood sugar over the past 3 months). Other studies show that vitamin D supplements don’t stop most people with prediabetes from developing diabetes.

Weight loss

Taking vitamin D supplements or eating foods that are rich in vitamin D does not help you lose weight.

What is vitamin D?

Vitamin D is the name given to a group of fat-soluble prohormones (substances that usually have little hormonal activity by themselves but that the body can turn into hormones). Vitamin D helps the body use calcium and phosphorus to make strong bones and teeth. Skin exposed to sunshine can make vitamin D, and vitamin D can also be obtained from certain foods. Vitamin D deficiency can cause a weakening of the bones that is called rickets in children and osteomalacia in adults.

Two major forms of vitamin D that are important to humans are vitamin D₂, or ergocalciferol, and vitamin D₃, or cholecalciferol. Vitamin D₂ is made naturally by plants, and vitamin D₃ is made naturally by the body when skin is exposed to ultraviolet radiation in sunlight. Both forms are converted to 25-hydroxyvitamin D in the liver. 25-Hydroxyvitamin D then travels through the blood to the kidneys, where it is further modified to 1,25-dihydroxyvitamin D, or calcitriol, the active form of vitamin D in the body. The most accurate method of evaluating a person’s vitamin D status is to measure the level of 25-hydroxyvitamin D in the blood.

Most people get at least some of the vitamin D they need through sunlight exposure. Dietary sources include a few foods that naturally contain vitamin D, such as fatty fish, fish liver oil, and eggs. However, most dietary vitamin D comes from foods fortified with vitamin D, such as milk, juices, and breakfast cereals. Vitamin D can also be obtained through dietary supplements.

The Institute of Medicine (IOM) of the National Academies has developed the following recommended daily intakes of vitamin D, assuming minimal sun exposure:

• For those between 1 and 70 years of age, including women who are pregnant or lactating, the recommended dietary allowance (RDA) is 15 micrograms (μg) per day. Because 1 μg is equal to 40 International Units (IU), this RDA can also be expressed as 600 IU per day.
• For those 71 years or older, the RDA is 20 μg per day (800 IU per day).
• For infants, the IOM could not determine an RDA due to a lack of data. However, the IOM set an Adequate Intake level of 10 μg per day (400 IU per day), which should provide sufficient vitamin D.

Although the average dietary intakes of vitamin D in the United States are below guideline levels, data from the National Health and Nutrition Examination Survey revealed that more than 80 percent of Americans had adequate vitamin D levels in their blood.

Even though most people are unlikely to have high vitamin D intakes, it is important to remember that excessive intake of any nutrient, including vitamin D, can cause toxic effects. Too much vitamin D can be harmful because it increases calcium levels, which can lead to calcinosis (the deposit of calcium salts in soft tissues, such as the kidneys, heart, or lungs) and hypercalcemia (high blood levels of calcium). The safe upper intake level of vitamin D for adults and children older than 8 years of age is 100 μg per day (4000 IU per day). Toxicity from too much vitamin D is more likely to occur from high intakes of dietary supplements than from high intakes of foods that contain vitamin D. Excessive sun exposure does not cause vitamin D toxicity. However, the IOM states that people should not try to increase vitamin D production by increasing their exposure to sunlight because this will also increase their risk of skin cancer.

Why are cancer researchers studying a possible connection between vitamin D and cancer risk?

Early epidemiologic research showed that incidence and death rates for certain cancers were lower among individuals living in southern latitudes, where levels of sunlight exposure are relatively high, than among those living at northern latitudes. Because exposure to ultraviolet light from sunlight leads to the production of vitamin D, researchers hypothesized that variation in vitamin D levels might account for this association. However, additional research based on stronger study designs is required to determine whether higher vitamin D levels are related to lower cancer incidence or death rates.

Experimental evidence has also suggested a possible association between vitamin D and cancer risk. In studies of cancer cells and of tumors in mice, vitamin D has been found to have several activities that might slow or prevent the development of cancer, including promoting cellular differentiation, decreasing cancer cell growth, stimulating cell death (apoptosis), and reducing tumor blood vessel formation (angiogenesis).

What is the evidence that vitamin D can help reduce the risk of cancer in people?

A number of epidemiologic studies have investigated whether people with higher vitamin D intakes or higher blood levels of vitamin D have lower risks of specific cancers. The results of these studies have been inconsistent, possibly because of the challenges in carrying out such studies. For example, dietary studies do not account for vitamin D made in the skin from sunlight exposure, and the level of vitamin D measured in the blood at a single point in time (as in most studies) may not reflect a person’s true vitamin D status. Also, it is possible that people with higher vitamin D intakes or blood levels are more likely to have other healthy behaviors. It may be one of these other behaviors, rather than vitamin D intake, that influences cancer risk.

Several randomized trials of vitamin D intake have been carried out, but these were designed to assess bone health or other non-cancer outcomes. Although some of these trials have yielded information on cancer incidence and mortality, the results need to be confirmed by additional research because the trials were not designed to study cancer specifically.

The cancers for which the most human data are available are colorectal, breast, prostate, and pancreatic cancer. Numerous epidemiologic studies have shown that higher intake or blood levels of vitamin D are associated with a reduced risk of colorectal cancer. In contrast, the Women’s Health Initiative randomized trial found that healthy women who took vitamin D and calcium supplements for an average of 7 years did not have a reduced incidence of colorectal cancer. Some scientists have pointed out that the relatively low level of vitamin D supplementation (10 μg, or 400 IU, once a day), the ability of participants to take additional vitamin D on their own, and the short duration of participant follow-up in this trial might explain why no reduction in colorectal cancer risk was found. Evidence on the association between vitamin D and the risks of all other malignancies studied is inconclusive.

How is vitamin D being studied now in clinical cancer research?

Taken together, the available data are not comprehensive enough to establish whether taking vitamin D can prevent cancer. To fully understand the effects of vitamin D on cancer and other health outcomes, new randomized trials need to be conducted. However, the appropriate dose of vitamin D to use in such trials is still not clear. Other remaining questions include when to start taking vitamin D, and for how long, to potentially see a benefit.

To begin addressing these issues, researchers are conducting two phase I trials to determine what dose of vitamin D may be useful for chemoprevention of prostate, colorectal, and lung cancers. In addition, larger randomized trials have been initiated to examine the potential role of vitamin D in the prevention of cancer. The Vitamin D/Calcium Polyp Prevention Study, which has finished recruiting approximately 2,200 participants, is testing whether vitamin D supplements, given alone or with calcium, can prevent the development of colorectal adenomas (precancerous growths) in patients who previously had an adenoma removed. The study’s estimated completion date is December 2017. The Vitamin D and Omega-3 Trial (VITAL) will examine whether vitamin D supplements can prevent the development of a variety of cancer types in healthy older men and women. The organizers of VITAL expect to recruit 20,000 participants and complete the trial by June 2016.

Researchers are also beginning to study vitamin D analogs--chemicals with structures similar to that of vitamin D--which may have the anticancer activity of vitamin D but not its ability to increase calcium levels.

Yes, getting too much vitamin D can be harmful. Very high levels of vitamin D in your blood (greater than 375 nmol/L or 150 ng/mL) can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones. Extremely high levels of vitamin D can cause kidney failure, irregular heartbeat, and even death. High levels of vitamin D are almost always caused by consuming excessive amounts of vitamin D from dietary supplements. You cannot get too much vitamin D from sunshine because your skin limits the amount of vitamin D it makes.

The daily upper limits for vitamin D include intakes from all sources—food, beverages, and supplements—and are listed below in micrograms (mcg) and international units (IU):

Yes, vitamin D supplements may interact with some medicines. Here are several examples:

• Orlistat (Xenical® and alli®) is a weight-loss drug. It can reduce the amount of vitamin D your body absorbs from food and supplements.
• Cholesterol-lowering statins might not work as well if you take high-dose vitamin D supplements. This includes atorvastatin (Lipitor®), lovastatin (Altoprev® and Mevacor®), and simvastatin (FloLipid™ and Zocor®)
• Steroids such as prednisone (Deltasone®, Rayos®, and Sterapred®) can lower your blood levels of vitamin D.
• Thiazide diuretics (such as Hygroton®, Lozol®, and Microzide®) could raise your blood calcium level too high if you take vitamin D supplements.

Tell your doctor, pharmacist, and other healthcare providers about any dietary supplements and prescription or over-the-counter medicines you take. They can tell you if the dietary supplements might interact with your medicines. They can also explain whether the medicines you take might interfere with how your body absorbs or uses other nutrients.