Vitamin D Deficiency: Causes, Treatment, and Prevention

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Vitamin D is a fat-soluble vitamin that is naturally occurring in some foods. Your skin also produces vitamin D when you are in the sun. It is essential facilitator of many bodily functions. Vitamin D's most important role is to keep your bones healthy by increasing your body’s ability to absorb calcium.  

When your body doesn’t get an adequate amount of vitamin D, your bones might become thin and brittle, making you more susceptible to fractures. Vitamin D also plays a role in preventing and possibly treating diabetes, high blood pressure, some types of cancer, and multiple sclerosis.

Signs of Low Vitamin D 

The most common sign of vitamin D deficiency is muscle weakness and bone pain. Some other symptoms of low vitamin D levels include: 

  • Weakness 
  • Mood swings 
  • Fatigue 

Vitamin D deficiency can cause osteoporosis, which causes bones to fracture easily. In children, it can cause rickets, a condition that causes the bones to become soft and bend.

Severe vitamin D deficiency can also cause a condition known as osteomalacia in adults. Osteomalacia causes muscle weakness, bone pain, and weak bones. 

Causes of Low Vitamin D 

A variety of factors, from medical conditions to aging, can be responsible for low vitamin D levels. 


With age, the skin’s natural ability to produce Vitamin D decreases. This contributes to vitamin D deficiency in older people. In older adults, there can be as much as a 50% reduction in the skin's vitamin D production.

Weight Loss Surgery

People who undergo weight-loss surgeries might be more susceptible to developing a vitamin D deficiency. This is because it becomes harder for them to consume the vitamins they need in sufficient quantities.

Insufficient Exposure to Sunlight

Your skin makes use of sunlight to produce vitamin D. When you have little or no exposure to the sun, it can’t do that. This means relying only on dietary supplies of vitamin D, which may be insufficient. People with darker skin also have difficulty producing sufficient amounts of vitamin D.

Insufficient Dietary Intake

It’s very important to ensure that our diet always contains all the vitamins and nutrients our bodies need to function properly. Fish, egg yolks, milk, and liver are excellent sources of vitamin D.

People who adhere to a vegan diet find it more difficult to incorporate vitamin D into their diets, as most of the richest sources of vitamin D are animal-based.

Vitamin D dietary supplements are a great option for people with a deficiency. Fortified orange juice also contains a substantial amount of vitamin D.

Medical Conditions

Some medical conditions may also cause vitamin D deficiency. These include: 

  • Kidney diseases 
  • Liver diseases 
  • Obesity 
  • Celiac disease 
  • Crohn’s disease 
  • Cystic fibrosis

Diagnosing Vitamin D Deficiency

Symptoms of vitamin D deficiency are common to many other conditions. To ensure that vitamin D deficiency is indeed the underlying cause of your symptoms, your doctor may recommend a 25-hydroxy vitamin D blood test.

This test helps measure the levels of vitamin D in your body. If your levels are less than 12 nanograms per milliliter (nmol/L), you will be diagnosed with vitamin D deficiency. The risk of inadequacy, however, can occur between 12 to 20 nanograms per milliliter (nmol/L).

The benefits of screening for vitamin D deficiency in adults without symptoms are still unclear, according to a recent statement by the U.S. Preventive Services Task Force (USPSTF). Therefore, routine screening isn't recommended unless you have symptoms or are in a higher risk category of deficiency. 

Who Is at Risk?

Some groups of people have an increased likelihood of developing vitamin D deficiency. They include: 

  • Those who are obese may be deficient in vitamin D because body fat can bind to vitamin D and prevent the body from absorbing it.
  • People with darker skin are less able to create sufficient amounts of vitamin D in their skin.
  • Pregnant women may be more prone to vitamin D deficiency due to increased demand to support fetal bone development.
  • People with fat malabsorption disorders may deal with vitamin D deficiency because it is a fat-soluble vitamin.
  • Infants who are breastfed may have a vitamin D deficiency because breast milk isn’t a great source of vitamin D.
  • People who take certain medicines like antifungal drugs and anti-seizure drugs are more prone to vitamin D deficiency because these medicines can affect the metabolism of vitamin D.

Treatment for Low Vitamin D 

The focus of treating vitamin D deficiency is raising vitamin D levels to a point where it’s adequate for normal body functioning. This can be done in a variety of ways including: 

  • Taking vitamin D supplements: Vitamin D supplements are available in two forms—D2 and D3. Vitamin D2, also known as ergocalciferol, is derived from plants. It is only available by prescription. D3, or cholecalciferol, is derived from animals. D3 supplements are available over the counter. 
  • Eating foods that are rich in vitamin D, such as cod liver oil, swordfish, tuna, salmon, milk, and liver: For people with vegan diets, a cup of fortified orange juice is also a great source of vitamin D.
  • Getting more sunlight safely by applying a broad-spectrum sunscreen before going in the sun: 10 to 15 minutes of sun exposure, two to three times a week, may be adequate for your skin to absorb enough vitamin D. If you have darker skin or are older you might want to spend some more time in the sun. 

Adults should get at least 600 international units (IUs) of vitamin D per day, either through diet or nutritional supplements. For people 70 years old and older, should IUs is recommended as their skin slows the production of vitamin D from the sun. However, people who are at a higher risk of developing vitamin D deficiency may need more than these recommended units. 

Infants should get at least 400 IUs and people who are pregnant and breastfeeding should get at least 600 IUs. Research suggests that people who are breastfeeding can take a high dose of vitamin D (6400 IUs) to satisfy their baby's vitamin D requirement. That means breastfeeding babies can skip supplementation.

A Word From Verywell

It is more difficult to treat vitamin D deficiency than to prevent it. Eating foods rich in vitamin D, using vitamin D supplements, and getting adequate sunlight is a great way to prevent low vitamin D levels in your body.

But it is possible to consume too much vitamin D. Even though vitamin D overdose is rare, you shouldn’t take higher than your daily recommended dosage of vitamin D without speaking to your doctor first. Signs of vitamin D overdose include nausea, constipation, weakness, and weight loss.

8 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. U.S. National Library of Medicine. Vitamin D deficiency.

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  5. Michos ED, Kalyani RR, Segal JB. Why USPSTF still finds insufficient evidence to support screening for vitamin D deficiencyJAMA Network Open. 2021;4(4). doi:10.1001/jamanetworkopen.2021.3627

  6. Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of deficiency: An Endocrine Society clinical practice guidelineJ Clin Endocrinol Metab. 2011;96(7):1911-30.

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By Toketemu Ohwovoriole
Toketemu has been multimedia storyteller for the last four years. Her expertise focuses primarily on mental wellness and women’s health topics.