Why Is Vitamin D Important?

Alexis Bryan
Alexis Bryan23 Aug 2022

Vitamin D, the "sunshine vitamin," is produced in the skin upon sun exposure. Almost 40% of Americans fall short of their optimal vitamin D levels. Signs of low vitamin D can be as subtle as fatigue, frequent illness, or back pain. Vitamin D is essential because of its wide range of benefits to our overall health. We spoke with two experts to learn more about the importance of vitamin D.

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Importance of Vitamin D

Like other vitamins, we can obtain vitamin D from the foods we eat or supplements we take, but our bodies also naturally convert ultraviolet-B (UVB) rays from the sun into vitamin D.

Vitamin D has a wide range of benefits for our health, including maintaining bone health, supporting our immune system, preventing cancer, and improving depression, among others. The seven key benefits of vitamin D are prevention of:

Bone Health

For our bodies to absorb calcium effectively, we need vitamin D. According to Nutritionist Lisa Richards, “Vitamin D is essential to allowing your body to use the calcium it is given to support bone growth and health. When vitamin D levels are low, this process is not as efficient, and our bones can become weak.”

Immune Support

Vitamin D is also essential in supporting our immune system. Allison Stock, Registered Dietician, explains, “Your immune system is very complex, but scientists have discovered that vitamin D receptors exist on the cells of your immune system. This means vitamin D is actively part of the process of fighting infections like the common cold and flu virus.

Mental Health

Like the immune system, your brain also has receptors for vitamin D. Research has shown low vitamin D levels are associated with a greater risk for symptoms of depression. In addition to that, several studies found vitamin D supplementation had a positive impact on depression scores. However, more research is needed to fully understand how vitamin D is involved in the pathology of depression.”

Symptoms of Low Vitamin D

Richards explains, “Signs and symptoms of a vitamin D deficiency can easily be passed off as just a side effect of your busy and exhausting lifestyle. But, chronic fatigue and other symptoms can be signs of a serious vitamin D deficiency.

While we may not notice this initially, the side effects of our chronic vitamin D deficiency may show up later in life through fragile bones.” The most common signs and symptoms of low vitamin D include:

  • Being sick or getting infections often
  • Fatigue and tiredness
  • Bone and back pain
  • Depression
  • Impaired wound healing
  • Bone loss
  • Hair loss
  • Muscle Pain

For children, signs of low vitamin D may include:

  • Irritability
  • Lethargy
  • Developmental delay
  • Bone changes
  • Bone fractures

There are, however, many ways you can increase vitamin D levels, such as:

  • Adding more vitamin D rich foods to your diet
  • Spending more time outside
  • Taking a vitamin D supplement

Foods With Vitamin D

There are two primary sources of dietary Vitamin D:

Vitamin D3 (cholecalciferol): Found in some animal foods, like fatty fish and egg yolks.

Vitamin D2 (ergocalciferol): Found in some plants, mushrooms, and yeasts.

If you are low in vitamin D, your doctor may recommend adding more vitamin-D-rich foods to your daily diet. Foods high in vitamin D include:

  • Fatty fish
  • Egg yolks
  • Fortified cereals
  • Milk and juices with added vitamin D
  • Yogurt
  • Beef liver
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Vitamin D Supplements

Vitamin D can be supplemented through a multivitamin or a vitamin D supplement. In supplements, the two forms of vitamin D are D2 (ergocalciferol) and D3 (cholecalciferol). While both forms work, D3 might raise vitamin D levels higher and longer than D2. Because vitamin D is fat-soluble, it is best absorbed when taken with a meal or snack that includes some fat.

Before taking a supplement, ask your doctor about the recommended dosage based on your vitamin D test results. 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).

Stock adds, “Another option for supplementation is to use cod liver oil. Just one teaspoon of cod liver oil contains 450 IUs of vitamin D (4), as well as vitamin A and omega- 3 fatty acids.”

Recommended Supplement Amount of Vitamin D by Age

Life StageRecommended Amount
Birth to 12 months10 mcg (400 IU)
Children 1–13 years15 mcg (600 IU)
Teens 14–18 years15 mcg (600 IU)
Adults 19–70 years15 mcg (600 IU)
Adults 71 years and older20 mcg (800 IU)
Pregnant and breastfeeding teens and women15 mcg (600 IU)

Vitamin D Testing

Before your body can use vitamin D, the liver converts vitamin D to a chemical known as 25-hydroxyvitamin D, also called calcidiol. The 25-hydroxy vitamin D test is best to monitor vitamin D levels. 

Vitamin D Test Results (level of 25-hydroxyvitamin)

< 30 nmol/LVitamin D deficiency
30-50 nmol/LPotential deficiency
50-125 nmol/L Normal range
Levels above 125 nmol/LHigh (may cause health problems)

Who Should Get Tested for vitamin D Deficiency

A vitamin D test is used to determine if you have a vitamin D deficiency and can also monitor the effectiveness of Vitamin D supplements. They are also commonly ordered to monitor Crohn's Disease, Cystic Fibrosis, and bone weakness.

Vitamin D tests can be ordered as part of a routine screening if you have no symptoms of low vitamin D, but if you are experiencing bone weakness, fatigue, or muscle cramps, it may be a good idea to get one anyway.

Those who are at high risk of having low levels of vitamin D, and may benefit from vitamin D testing, include:

  • People who don’t get much exposure to the sun
  • Older adults
  • People with obesity
  • Babies who are breastfed only (formula is usually fortified with vitamin D)
  • People who have had gastric bypass surgery
  • People who have a disease that affects the intestines and makes it difficult for the body to absorb nutrients, such as Crohn’s disease

Vitamin D Frequently Asked Questions (FAQs)

The sunshine vitamin, vitamin D, plays a vital role in our health. However, many people are low in vitamin D and may benefit from adding vitamin D-rich foods or supplements to their diet. Below we answer a few common questions.

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Do I get enough Vitamin D from the sun?

Sun exposure rarely provides adequate vitamin D unless you spend sufficient amounts of time in the sun all year long. To get enough vitamin D from the sun, you must expose the majority of your body to UVB rays.

Spending extended time in the sun can also raise concern for premature skin aging and skin cancer, but if you use sunscreen, you will produce less vitamin D. Depending on your skin type, consider spending 10-30 minutes in the sun before applying sunscreen to get optimal amounts of vitamin D.

What are the risk factors for low vitamin D?

Certain factors at play can impact your vitamin D levels. Some reasons why your vitamin D levels may be low are because you: 

  • Live in a northern climate or where it's very cloudy with little to no sun
  • Have a darker skin tone
  • Are overweight or obese
  • Spend much of the day indoors
  • Wear sunscreen frequently
  • Have a digestive disorder such as Crohn's or Celiac Disease

How much do vitamin D supplements cost?

Generally, prices range from $0.03–$1.67 per serving, or $12.39–$49.95 per container, though this may vary depending on where you shop. Note that serving sizes are generally 1 or 2 capsules per day. Liquid supplement dosages range from 1–5 drops or pumps daily.

When looking for a good vitamin D supplement, Stock recommends, “look for a supplement that is independently verified for quality by ConsumerLab.com, NSF International, or US Pharmacopeial (USP). Dietary supplements are not regulated by the Food and Drug Administration (FDA), so it’s even more important to do your homework and talk to your healthcare practitioner before starting any new supplement.”

Should I take a vitamin D supplement?

Even though vitamin D is essential, and many people are low in vitamin D, buying a high-dose supplement without testing is not recommended. You should take a vitamin D supplement if you get your Vitamin D levels checked and the results show your levels are less than 50-125 nmol/L or your doctor recommends supplementation.

Feeling fatigued or being sick frequently can be signs of low vitamin D, but those symptoms can also be attributed to another medical condition. Using supplements without your provider’s recommendation can do more harm than good. Check with your doctor to determine if you should take a vitamin D supplement.

Bottom Line

Vitamin D can support your health in several ways, and vitamin D deficiency can cause health concerns. As part of your annual health check-up, ask your doctor to order a Vitamin D test in addition to any other tests they recommend.

Allison Stock, RD, and creator of The Fruitful Female is a Registered Dietitian and Nutritionist with over a decade of experience giving consumers food & nutrition information in blog articles, webinars, and e-learning courses.

Lisa Richards is a nutritionist and author of the Candida Diet. She has been featured on Today, US News, Women’s Health magazine, Huffington Post, Healthline, the San Francisco Chronicle, Reader’s Digest, Lifehack, Insider, and Well+Good, among others. Through her website, thecandidadiet.com, she explains the benefits of a low-sugar, anti-inflammatory diet.

Alexis Bryan

Alexis Bryan MPH, is a recent graduate of Columbia’s Mailman School of Public Health. She is passionate about increasing access to care to improve health outcomes. Outside of work, she loves to travel, read, and pay too much attention to her plants.