There has been debate recently about how much vitamin D people need to stay healthy—and how to tell whether we get enough of it—and, in truth, it’s complicated. But one thing experts agree on is that vitamin D is vital to our health. Without exposure to natural sunlight or eating foods rich in vitamin D, we may not maintain adequate amounts of the vitamin. That’s a problem because vitamin D deficiency can be harmful to bones and muscles.

Vitamin D deficiency affects people across the lifespan. Breastfed babies don’t get enough vitamin D from breast milk, so they need to take supplements. As people age, it’s harder for their skin to produce adequate amounts of vitamin D, which may lead to deficiency.

The actual prevalence of vitamin D deficiency depends on what is defined as a level of vitamin D in the blood that is considered sufficient to maintain musculoskeletal health. The Institute of Medicine has concluded that a level between 20-50 ng/mL of 25-hydroxyvitamin D will allow for this. This range of values is consistent with the prevailing view in Europe. However, there are professional societies in the United States that feel that a level of at least 30 ng/ml is required for optimal skeletal health.

“In our view, the preponderance of evidence supports the 20-50 ng/mL range, although it is also true that in some disease states a higher level may be required,” says Karl Insogna, MD, Ensign Professor of Medicine (endocrinology), and Thomas Carpenter, MD, professor of pediatrics (endocrinology) and of orthopaedics and rehabilitation at Yale School of Medicine. “Regardless of what level your physician decides constitutes vitamin D deficiency, therapy and prevention of vitamin D deficiency are straightforward, relatively inexpensive, and safe. We don’t feel that there is any measurable benefit when 25-hydroxyvitamin D levels exceed 50 ng/mL.”

Vitamin D deficiency is the state of having inadequate amounts of vitamin D in your body, which may cause health problems like brittle bones and muscle weakness. There may be no symptoms and doctors don’t routinely check vitamin D levels, so many people are deficient and don’t realize it.

Vitamin D helps the body absorb calcium and phosphorus, which are important to bone health. When a person is very vitamin D deficient, they cannot absorb dietary calcium well; having adequate levels is important to absorb enough calcium from your diet. Healthy vitamin D levels also help to improve phosphorus absorption from your diet.

People typically get enough vitamin D from sun exposure: When sunlight hits the skin, the skin converts that ultraviolet radiation to vitamin D. People also get vitamin D from certain foods—including fish, egg yolks, and fortified milk and cereal—or dietary supplements.

When vitamin D levels are low and the body isn’t able to properly absorb calcium and phosphorus, there is an increased risk of bone pain, bone fractures, muscle pain, and muscle weakness. In older adults, severe vitamin D deficiency (levels less than 10 ng/mL) may also contribute to an increased risk of falls.

People who don’t have adequate levels of vitamin D may be deficient for any of these reasons:

• Not enough exposure to sunlight
• Darker skin pigment
• Malnutrition
• Kidney or liver failure, which prevents the body from adequately processing vitamin D
• Certain medications
• Certain types of cancer, such as lymphoma
• A family history of vitamin D deficiency or childhood rickets

“It is important to note that ‘normal’ vitamin D levels have largely been determined in Caucasian populations. African Americans tend to have lower levels of vitamin D. Much of vitamin D in the blood is bound to carrier proteins, but emerging evidence indicates that when the “free,” unbound fraction of vitamin D is measured, it tends to be lower as well,” say Drs. Insogna and Carpenter. “Therefore, defining vitamin D deficiency in this population requires a consideration of other factors, such as the levels of parathyroid hormone in the blood and the levels of calcium in blood and urine.”

Additionally, some people have health conditions that make it difficult for them to absorb vitamin D, including:

• Inflammatory bowel disease (Crohn’s disease or ulcerative colitis)
• Celiac disease
• Cystic fibrosis
• People who have had bariatric surgery for weight loss
• People who have had sections of the small intestine removed (resection)
• A condition affecting the pancreas, such as exocrine pancreatic insufficiency

It has been suggested that vitamin D deficiency may play a role in certain conditions, such as fibromyalgia, chronic fatigue syndrome, and multiple sclerosis. However, a firm causal link between vitamin D deficiency and these—and other—conditions, along with the therapeutic benefits of vitamin D supplementation, has yet to be established.

Most people with vitamin D deficiency don’t notice any symptoms. Others may notice vague symptoms that may be signs of any number of conditions.  

Possible symptoms include:  

• Muscle pain
• Bone pain
• Increased sensitivity to pain
• A tingly, “pins-and-needles” sensation in the hands or feet
• Muscle weakness in body parts near the trunk of the body, such as the upper arms or thighs
• Waddling while walking, due to muscle weakness in the hips or legs
• A history of broken bones
• Muscle twitches or tremors
• Muscle spasms
• Bowed legs (when the deficiency is severe)

Because there are often no symptoms, identifying vitamin D deficiency can be difficult. While a blood test that checks vitamin D levels can be used for diagnosis, it is not routinely ordered for all patients. Doctors typically order this test if a patient reports such symptoms as bone or muscle pain or has other health conditions that may indicate risk for vitamin D deficiency.

Doctors may ask about a personal or family history of rickets, osteoporosis, or bone fractures.

Eating more vitamin D-rich foods isn’t usually sufficient to correct vitamin D deficiency, so your doctor is likely to recommend treatment with supplements.

The dosage of vitamin D that doctors recommend may vary, depending on severity, age, weight and whether you’re pregnant or breastfeeding. Prescription-strength doses and dietary supplements are available. Some prescription doses are given weekly, rather than daily.

Types of vitamin D supplementation include:

• Vitamin D₂ supplements (ergocalciferol), which are derived from a plant source; Drisdol® is a trade name for a vitamin D₂ product.
• Vitamin D₃ supplements (cholecalciferol), which come from an animal source.
• Calcidiol, a medication that’s a form of vitamin D₃, which may be prescribed when an individual has a health condition that leads to malabsorption, like cystic fibrosis or celiac disease

It’s also important to make sure you are consuming enough calcium. People who have adequate levels of both vitamin D and calcium are able to lower their risk of fractures, but this isn’t the case when people only have adequate levels of vitamin D and inadequate levels of calcium.

Depending on other health conditions, your doctor may also prescribe:

• Medications to help strengthen bones and to lower the risk of osteoporosis and fractures

Ensuring a normal vitamin D level in patients with fat malabsorption issues, including cystic fibrosis and Crohn’s disease, can be challenging and may require very high doses of supplements.

You may also be encouraged to eat foods that are rich in vitamin D, including:

• Certain fish, including tuna, salmon, and sardines
• Egg yolks
• Milk and other foods that have been fortified with vitamin D, such as breakfast cereals and orange juice

Some doctors also recommend exposing the skin on your arms, legs, and/or face to natural sunlight for 15 minutes, three or more times per week, which helps your skin produce vitamin D. Other doctors discourage this, because direct exposure to sunlight without sunscreen may increase the risk of skin cancer.

Vitamin D deficiency is highly treatable. If you are diagnosed with the condition and follow treatment recommendations, you will likely be able to increase your intake to an acceptable level, which should eliminate any symptoms or long-term problems.

“Until recently, there was no generally accepted “gold standard” for vitamin D that could be used to determine how accurate a given assay was for determining vitamin D levels,” says Dr. Insogna. “Such a standard is now available, and the Yale Mineral Metabolism laboratory that I direct adapted this standard in our assay very early on. We have a research interest in this area and also measure vitamin D levels for practitioners in our health system. Consequently, we pay particular attention to any new developments in the important area of vitamin D and musculoskeletal health.”