What Does Vitamin D Do for the Body?

What Does Vitamin D Do for the Body?

Here’s an interesting fact about vitamin D: it’s not a vitamin! It’s actually a hormone that acts like a fat-soluble vitamin in the body with the most active form being vitamin D3.1 Another interesting aspect of vitamin D is that when the sun shines on bare skin, the body makes vitamin D.2 And finally, the most important attribute of vitamin D is that it helps support health on many levels.2

Vitamin D Benefits for Mood and More

Because there are vitamin D receptors in almost every tissue and cell of the body, vitamin D helps support several key body functions including mood, heart, bones, teeth, and immunity.3,4 

Vitamin D plays a significant role in supporting calcium and mineral balance, which makes it a great vitamin for bones and teeth.5 

Having adequate vitamin D levels is also important to mental health.6 Along with mood, research also shows that vitamin D helps support immune function.7

In addition to sun exposure, vitamin D is available in some fortified foods and as a dietary supplement. 

Are You Getting Enough Vitamin D?

It’s difficult to get enough vitamin D through diet because very few foods naturally contain vitamin D with the primary sources being fatty fish and fish liver oils.8 The Recommended Dietary Allowance (RDA) of vitamin D for adults 19 – 69 years is 600 IU and for individuals 70 years and older, the RDA is 800 IU.8

According to the National Institutes of Health, it’s estimated that one in four Americans have low vitamin D levels. Here are a few reasons you may not be getting enough vitamin D:2

  • Clouds, smog, sunscreen, and lack of sun exposure.

  • Very few non-fortified foods contain vitamin D.

  • If you are older, overweight, or have dark skin.

Even if there are no signs of low vitamin D levels, many doctors presently recommend periodically doing a simple blood test to measure levels.9

Taking a vitamin D supplement daily may be the best way to ensure you are getting enough of this important nutrient. D3 + K2 is a combined supplement form of vitamins D and K. When the two are combined, it may help support bones, mood and more.*

Follow @zhou_nutrition for more fitness and wellness tips!

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


  1. Pike JW, Christakos S. Biology and Mechanisms of Action of the Vitamin D Hormone. Endocrinol Metab Clin North Am. 2017;46(4):815-843. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5762112/?report=reader
  2. National Institutes of Health Office of Dietary Supplements. Vitamin D fact sheet for consumers. 2022;Nov 8. https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
  3. Chauhan K, Shahrokhi M, Huecker MR. Vitamin D. StatPearls. 2023;Jan. https://www.ncbi.nlm.nih.gov/books/NBK441912/?report=reader#_NBK441912_pubdet_
  4. Pilz S, Zittermann A, Trummer C, et al. Vitamin D testing and treatment: a narrative review of current evidence. Endocr Connect. 2019;8(2):R27-R43. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6365669/?report=reader
  5. Botelho J, Machado V, Proença L, Delgado AS, Mendes JJ. Vitamin D Deficiency and Oral Health: A Comprehensive Review. Nutrients. 2020;12(5):1471. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7285165/?report=reader
  6. Menon V, Kar SK, Suthar N, Nebhinani N. Vitamin D and Depression: A Critical Appraisal of the Evidence and Future Directions. Indian J Psychol Med. 2020;42(1):11-21. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6970300/?report=reader
  7. Martens PJ, Gysemans C, Verstuyf A, Mathieu AC. Vitamin D's Effect on Immune Function. Nutrients. 2020;12(5):1248. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7281985/?report=reader
  8. Harvard School of Public Health. Vitamin D. Nutrition Source. 2023;March. https://www.hsph.harvard.edu/nutritionsource/vitamin-d/
  9. National Institutes of Health. Vitamin D test. Medline Plus. 2022;June 2. https://medlineplus.gov/lab-tests/vitamin-d-test/