Vitamin D Deficiency: Symptoms, Causes, and How to Test Your Levels

Vitamin D plays an important role in keeping your bones, muscles, and immune system healthy. But many people do not get enough. In fact, about 1 in 3 U.S. adults may have low vitamin D levels.¹ Even more importantly, vitamin D deficiency can be hard to recognize because many people have no obvious symptoms.

Understanding the signs of low vitamin D and knowing when to get tested can help you take a closer look at your health.

What Is Vitamin D and Why Does It Matter?

Vitamin D is sometimes called the “sunshine vitamin” because your body can make it when your skin is exposed to sunlight. When ultraviolet B (UVB) rays from sunlight reach your skin, they trigger a chemical reaction that converts a form of cholesterol in your skin into vitamin D3. Your liver and kidneys then process vitamin D3 into a form your body can use. You can also get vitamin D from certain foods, fortified foods, and dietary supplements.

Vitamin D helps your body absorb calcium, which supports strong bones. It also plays a role in muscle function and immune system health.² Because your body relies on several steps to make and use vitamin D, factors such as limited sun exposure, darker skin, age, and certain health conditions can affect your vitamin D levels.

Vitamin D2 vs. D3

Vitamin D comes in two main forms: D2 and D3. Both can increase vitamin D levels, but vitamin D3 is generally more effective at raising and maintaining levels in the blood.²

Signs and Symptoms of Low Vitamin D

Vitamin D deficiency is often silent. When symptoms do occur, they may be easy to overlook or attribute to other causes.

Possible signs of low vitamin D include:

• Fatigue: You may feel unusually tired or lack energy.
• Bone or muscle pain: Low levels can contribute to bone discomfort, muscle weakness, or aches.
• Frequent illness: Vitamin D supports immune function, although its relationship with infections is still being studied.
• Low mood: Some people with low vitamin D report depression or changes in mood.
• Hair loss: Severe deficiency may be associated with certain types of hair loss.
• Slow wound healing: Vitamin D may play a role in the body's healing process.

Long-term deficiency can affect bone health. In adults, severe deficiency can contribute to osteomalacia, a condition that causes soft and weakened bones. In children, it can cause rickets (a condition in children where bones become soft and weak).²

What Causes Low Vitamin D?

Several factors can increase the risk of vitamin D deficiency, including:

• Limited exposure to sunlight
• Having darker skin
• Older age
• Obesity or other metabolic conditions
• Living farther from the equator
• Spending most of your time indoors or working overnight
• Conditions that affect nutrient absorption, such as celiac disease or Crohn’s disease
• Certain kidney or liver conditions

If one or more of these factors apply to you, testing may help determine whether your vitamin D levels are low.

How Is Vitamin D Deficiency Diagnosed?

The most common way to check vitamin D levels is a blood test called the 25-hydroxyvitamin D test, also known as the 25(OH)D test.²

A blood level below 20 ng/mL is generally considered deficient, while 21–29 ng/mL may be considered insufficient.² Your results should be interpreted in the context of your overall health.

A Vitamin D blood test can provide a clearer picture of your current levels.

How to Increase Your Vitamin D Levels

There are three main ways to increase vitamin D: sunlight, food, and supplements.

Adults ages 19–70 generally need 600 IU of vitamin D per day, while adults 71 and older need 800 IU. The upper limit for adults is 4,000 IU per day.² More is not always better, so talk with a healthcare professional before taking high-dose supplements.

Foods High in Vitamin D

Vitamin D-rich foods include:

• Salmon, trout, tuna, and sardines
• Egg yolks
• Beef liver
• UV-exposed mushrooms
• Fortified milk and plant-based milk
• Fortified orange juice and cereals

When to Get Tested for Vitamin D

Because vitamin D deficiency may not cause noticeable symptoms, testing can be one way to better understand your levels, particularly if you have risk factors for deficiency.

If you want to learn more about your vitamin D levels, explore the Vitamin D blood test available through Care Access. You can also explore other health screening opportunities to learn more about your health.