Essential Guide to Vitamin D

May 21, 2021 Bone HealthImmune SystemVitamin D 7 MIN

what is Vitamin D

What is Vitamin D?

Wondering where Vitamin D comes from? Vitamin D is a fat-soluble vitamin that has emerged as a popular nutrient over the past decade. It's known as the sunshine vitamin therefore the sun is the main source but there are other ways to get Vitamin D as it can be found in some foods and some fortified foods. Vitamin D was discovered in the early 1900s as an anti-rickets compound and consequently added to several food sources (e.g. dairy) through mandatory U.S. fortification programs in the 1930s. Today, instances of rickets in the U.S. population are rare. Ever since its discovery, Vitamin D has been considered a key vitamin essential for overall health.1

What Does Vitamin D Do and Why is Vitamin D Important?

So, what does Vitamin D do exactly? Below we’ll be answering, “What is Vitamin D good for?” and explain how it helps support the body. The main reasons Vitamin D is important include: 

  • Bone health support: Vitamin D helps build and support strong bones by enhancing calcium absorption, regulating calcium and phosphorus concentrations in the body, and regulating the bone cells involved in bone remodeling.2-3,†
  • Muscle health support: Vitamin D is important for muscle health because it supports muscle function, muscle strength, and balance.4,†
  • Immune health support: Receptors for Vitamin D are found in most immune cells. Research suggests that Vitamin D benefits may improve natural immune function and is necessary for a proper immune response. 

Is Vitamin D Deficiency a Growing Problem?

Unfortunately, yes. Too many Americans are not getting enough of this important nutrient. The 2020-2025  USDA Dietary Guidelines for Americans Committee identified Vitamin D as a “nutrient of public health concern,” as 9 out of 10 Americans fail to meet their daily Vitamin D needs.5 Many Americans don't meet the minimum requirement of sun exposure of 5 to 30 minutes a day/two times a week. Vitamin D deficiency is even more pronounced among people living in northern parts of the country, such as Seattle and New England, especially in the winter, due to limited access to sunlight. Vitamin D insufficiency is prevalent in particular segments of the population, including those with darker skin pigmentation, the elderly, obese individuals, and those living in geographical areas with limited sunlight.6

Are You at Risk for Vitamin D Insufficiency or Deficiency?

You may be at risk if any of the following apply:

  • Older Age/Darker Skin – Older adults and individuals with darker skin  do not make Vitamin D in skin from UVB rays as efficiently. 
  • Overweight/Obese – These individuals have an increased need for Vitamin D. 
  • Get limited sun exposure – You may have an increased need for vitamin D by staying indoors,are restricted to indoor activity, wear sunscreen and/or live at higher latitude or in a region with a long winter season or air pollution
  • Certain health conditions – Having a malabsorption syndrome, liver disease, or renal disease can increase your need for vitamin D.
  • Medications -  Some medications may interact with Vitamin D absorption or metabolism

Signs & Symptoms of Vitamin D Deficiency / Low Vitamin D Levels

Getting enough Vitamin D is important to support your overall health. Identifying whether you have low blood levels of vitamin D can be tricky because the signs and symptoms of inadequate amounts in the body can be subtle, so they often remain unlinked to an insufficient Vitamin D intake. If you belong to one of the groups listed above that is at higher risk for low vitamin D, you will want to take extra notice of whether any of these signs apply to you.

Our health professionals have compiled a list of the most common signs that you may have Vitamin D deficiency:

  • Regularly feeling excessively fatigued or tired. Given the important role of Vitamin D in maintaining cellular function, reduced amounts of Vitamin D can make you feel tired and unusually fatigued.
  • Getting sick often, especially with a cold or the flu. Vitamin D plays a crucial role in supporting the immune system. If you don’t get enough of it, you will fall sick with infections more often.
  • Weakened bones. Vitamin D helps your body absorb calcium, so not getting enough Vitamin D can negatively impact your bone health. Studies have shown that Vitamin D deficiency causes loss of bone density, and is a contributing factor to back pain.7
  • Muscle weakness or cramps. Vitamin D plays a crucial role in supporting muscle function and health. If you don’t get enough Vitamin D, your muscles can become weak, and you could experience muscle aches and cramps.

What are the Best Sources of Vitamin D?

For most Americans, sunlight exposure provides the main source of our Vitamin D requirements that help support healthy bones and our immune system. Few foods naturally contain Vitamin D, but those that do include certain fatty fish (such as salmon, mackerel, and sardines), fish liver oils, and egg yolks. To prevent rickets, the US began fortifying dairy and cereal with Vitamin D in the early 20th century. Unfortunately, you have to consume large amounts of these natural or fortified food sources to meet your Vitamin D needs. For example, one tablet or softgel of Nature Made Vitamin D3 25 mcg (1,000 IU) contains the same amount of Vitamin D as: †

  • 7 cans of tuna (3 oz cans)
  • 8 cups of fortified milk
  • 25 egg of yolks
  • 25 cups of fortified cereal8

The Vitamin D content per serving of other common foods that are sources of nutritional Vitamin D is listed here. Do you regularly consume these foods as a source of Vitamin D or get regular sunlight exposure on a daily basis? If not, you might want to know what foods have Vitamin D and consume them in your diet and consider a vitamin D supplement to help maintain an adequate level of vitamin D in the body. Be sure to get your Vitamin D levels checked so that you know what your body needs.

Vitamin D Food Sources

How Much Vitamin D?

1 cup or orange juice, Vitamin D fortified 

137 IU

Yogurt (6 oz.), Vitamin D fortified 

80 IU

Soy, almond, or oat milk, Vitamin D fortified 

100 to 144 IU

Cheddar cheese (1 oz.) 

12 IU

Mushrooms (white, ½ cup)

366 IU

Rainbow trout (cooked, 3 oz.)

645 IU

What is the Difference Between Vitamin D2 and Vitamin D3?

Vitamin D is available in two forms: Vitamin D2 (plant-derived) and Vitamin D3 (animal derived). Vitamin D3 is the preferred form because it has been shown to be more effective than Vitamin D2 at raising and maintaining Vitamin D levels in your body.9 Vitamin D3 is the form most commonly found in nutritional supplements; the D2 form is mostly found as a prescription.

How Do I Know How Much Vitamin D I Need?

To determine how much Vitamin D you should supplement per day, your doctor or healthcare provider can perform a simple blood test (serum 25-hydroxyVitamin D) to check your blood Vitamin D level. To correct deficiency, the Endocrine Society recommends 150 mcg (6000 IU) Vitamin D daily for 8 weeks.10 However, we recommend that you talk to your doctor to determine the appropriate supplement amount that is right for you.

How Much Vitamin D Should I Take Daily?

There is much debate as to the appropriate level of Vitamin D to recommend. Studies continue to emerge using varying dosages of Vitamin D. The Institute of Medicine recommends 15 to 20 mcg (600 - 800 IU) of Vitamin D daily to support bone health.11,† The Endocrine Society has also released clinical guidelines that are routinely used by health care practitioners who are working with patients to raise their blood levels of Vitamin D. These guidelines recommend 37.5 - 50 mcg (1500 - 2000 IU) Vitamin D daily for adults to support consistent blood levels of Vitamin D and help those with inadequate Vitamin D intake meet their daily nutrient needs.11 Consider adding a vitamin D supplement to help support an adequate vitamin D level in the body.

Be proactive with your health and consider taking a Vitamin D supplement as part of a healthy supplement regimen.

Learn More About Important Vitamins & Supplements:

This information is only for educational purposes and is not medical advice or intended as a recommendation of any specific products. Consult your health care provider for more information.

† These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.


  1. Hossein-nezhad A, Holick MF. Vitamin D for health: a global perspective. Mayo Clin Proc. 2013;88(7):720-755.
  2. Fleet JC, Schoch RD. Molecular mechanisms for regulation of intestinal calcium absorption by vitamin D and other factors. Crit Rev Clin Lab Sci. 2010;47(4):181-195.
  3. Von Hurst PR, Stonehouse W, Kruger MC, Coad J. Vitamin D supplementation suppresses age-induced bone turnover in older women who are vitamin D deficient. J Steroid Biochem Mol Biol. 2010;121:293-296.
  4. Ceglia L, Harris SS. Vitamin D and its role in skeletal muscle. Calcif Tissue Int. 2013;92(2):151-162.
  5. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2015 – 2020 Dietary Guidelines for Americans. 8th Edition. December 2015. Available at
  7. Cleveland Clinic. “Vitamin D Deficiency.” Retrieved on: March 16, 2021.
  8. U.S. Department of Agriculture, Agricultural Research Service. 2012. USDA National Nutrient Database for Standard Reference, Release 25. Nutrient Data Laboratory Home Page,
  9. Tripkovic L, Lambert H, Hart K, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr 2012;95:1357-1364.
  10. Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol & Metab. 2011;96(7):1911-1930.
  11. Food and Nutrition Board, Institute of Medicine (IOM). Dietary Reference Intakes for Vitamin D and Calcium. Washington, DC: National Academy Press, 2011.


Lynn M. Laboranti, RD

Science and Health Educator

Lynn is a Registered Dietitian (R.D.) and is a member of the Medical and Scientific Communications team at Pharmavite. She has over 20 years of experience in integrative and functional nutrition and has given lectures to health professionals and consumers on nutrition, dietary supplements and related health issues. Lynn frequently conducts employee trainings on various nutrition topics in addition to educating retail partners on vitamins, minerals and supplements. Lynn has previous clinical dietitian expertise in both acute and long-term care, as well as nutrition counseling for weight management, diabetes, and sports nutrition. Lynn earned a bachelor’s of science in Nutrition with a minor in Kinesiology/Exercise Science from The Pennsylvania State University. She earned a M.S. degree in Human Nutrition from Marywood University in Scranton, Pennsylvania. Lynn is an active member of the Academy of Nutrition and Dietetics, Sports Cardiovascular and Wellness Nutritionists, Dietitians in Functional Medicine, and holds a certification in Integrative and Functional Nutrition through the Academy of Nutrition and Dietetics.

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