What is vitamin D deficiency: causes, symptoms, and treatment

Since our bodies convert sunlight to vitamin D, the primary cause of vitamin D deficiency is underexposure to sunshine.
The symptoms of vitamin D deficiency include osteoporosis, muscle and bone pain, and frequent fatigue.
You can get more vitamin D by spending at least 5 to 10 minutes outside 3 times a week without sunscreen.
This article was reviewed by Melissa Rifkin, MS, RD, CDN, owner of Melissa Rifkin Nutrition LLC.
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Vitamin D is an essential vitamin that plays a role in your immune system and helps your body absorb calcium. Yet, many people don’t get enough vitamin D, particularly if you don’t live in a sunny climate. Here’s how to make sure you’re getting your daily dose.

Vitamin D deficiency is often caused by a lack of sunlight

Our bodies produce vitamin D with help from the sun. When you are exposed to the ultraviolet rays in sunlight, specific cholesterol molecules in your skin, called 7-dehydrocholesterol, turn into vitamin D.

Therefore, it’s hard to get enough vitamin D if you don’t live in a sunny climate. For this reason, many foods in the US are fortified with vitamin D, including milk, yogurt, orange juice, and cereal. There are also a few foods naturally rich in vitamin D including eggs and fatty fish like tuna and salmon.

Even with the food fortification efforts, however, an estimated 40% of US adults are vitamin D deficient. This means that many of us may be at risk for serious health problems like bone disease. That’s because you need vitamin D to absorb calcium, an important mineral that helps build bone density and keeps your bones strong. In fact, without adequate amounts of vitamin D, you absorb half as much calcium.

In addition to the lack of sunlight, other risk factors for having a vitamin D deficiency include obesity and avoiding dairy. Moreover, historically, scientists believed that people with darker skin are at greater risk for vitamin D deficiency, but there has been some controversy over whether this is true. Some experts have reported that vitamin tests may not accurately show how much vitamin D is active in the body and give falsely low results for African Americans.

A 2016 study on vitamin D levels responded to this controversy by including additional measures of vitamin D that factored in racial differences. This study showed that black Americans do have lower levels of vitamin D than whites and that they benefit just as much from taking vitamin D supplements, though they say that more research is still needed.

Symptoms of Vitamin D deficiency

The average adult needs around 600 international units (IU) of vitamin D a day. For reference, a serving of salmon contains roughly 400 IU.

However, if you don't eat a lot of fortified foods or go out in the sun every day, you may want to look out for the symptoms of vitamin D deficiency.

Vitamin D deficiency can cause Osteomalacia and Osteoporosis, conditions where your bones become less dense, says Kelly Springer, a registered dietitian.
When vitamin D deficiency leads to bone diseases, you may experience muscle and bone pain and you may be more likely to fracture or break a bone.
In infants and children, not getting enough vitamin D can lead to rickets, a condition that causes delayed growth, muscle weakness, and skeletal deformities.
Getting more frequent colds or respiratory infections may be another symptom. Vitamin D helps keep your immune system working well, so a deficiency can reduce your chance of fighting off sickness.
In women, vitamin D deficiency has also been linked to feeling fatigued.
"Vitamin D has some links to depression," Springer says, but adds that there is still more research needed before doctors recommend vitamin D supplements to treat depression.

How to treat Vitamin D deficiency

One of the most important changes you can make to raise your vitamin D levels is to get more sunlight. "Try to get at least 5-10 minutes outside 3 times a week without sunscreen," Springer says. This is most effective when your skin is directly exposed to the sun and not covered by clothing.

If you aren't able to get much sunlight, you can also make dietary changes as well. "During the winter months, try consuming foods that contain vitamin D or taking a supplement," Springer says.

You can also boost your vitamin D using a UV lamp, much like the type used for indoor tanning. This is particularly helpful for people with certain medical conditions who can't absorb vitamin D from supplements.

When choosing a supplement, Springer recommends that most people should aim for 600 units per day, while older adults are recommended to have 800 units per day. Moreover, the Mayo Clinic says that you can safely take 1,000 to 2,000 IU per day from supplements.