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The Ongoing Problem of Low Vitamin D Levels 

41%

OF U.S. ADULTS HAVE VITAMIN D INSUFFICIENCY 4

UP TO 60%

OF U.S. NURSING HOME RESIDENTS HAVE VITAMIN D DEFICIENCY 5,6

50%

OF PEOPLE GLOBALLY HAVE VITAMIN D INSUFFICIENCY 7

Hear what the experts have to say…

TRAILER: Multiple benefits of vitamin D (1:08)

TRAILER: Vitamin D levels (1:32)

TRAILER: Vitamin D and pneumonia (1:47)

Visit the “Meet the Experts” page for more…

The Importance of Vitamin D

What percentage of Americans are vitamin D deficient or insufficient?

The prevalence of vitamin D deficiency was found to be 28.9% and vitamin D insufficiency 41% in a subset of 26,010 US adults surveyed as part of the ongoing National Health and Nutrition Examination Survey (NHANES) 2001-2010. 1 Vitamin D deficiency is a major health concern because it has been linked to depression, fatigue, muscle aches, increased risk of respiratory infections, autoimmune disorders, osteoporosis, osteomalacia, osteoarthritis, increased risk of infection and some cancers. Vitamin D insufficiency has been associated with reduced calcium absorption, decreased bone density, potential mild decrease of the blood calcium level, accelerated bone resorption, an increased risk of falls, and potentially fractures. Vitamin D deficiency and insufficiency can seriously affect a person’s quality of life. 2,3,4

How is vitamin D different than other vitamins?

Unlike other vitamins, vitamin D is a prohormone. Dietary vitamin D first goes to the liver then the kidney converts it to its active form and distributes the active form throughout the body, which by definition makes vitamin D a “hormone-like” vitamin. Meaning it is synthesized and released from an endocrine organ, the kidneys. Vitamin D receptors are located throughout the body which helps explain why vitamin D is important for so many aspects of health. 8

Who is more at risk of vitamin D deficiency or insufficiency?

In the U.S., seniors, South Asians, Hispanics and non-Hispanic Blacks are groups that have a higher prevalence of low vitamin D levels. Other situations that may lead to vitamin D deficiency or insufficiency include limited sun exposure, fat malabsorption conditions (such as celiac disease), and obesity. 5,6,7

What is the importance of vitamin D in the body?

Vitamin D was first known for its role in bone health and plays a key role in the metabolism, or cellular processes, of calcium and phosphorus, which are needed for bone integrity. Vitamin D has many other important functions too. It plays a key role in the immune system, oral health, as well as muscle health and strength. Vitamin D is also involved in regulating gene transcription and promoting protein synthesis. All of these critical functions make vitamin D important for multiple aspects of human health. 9

Vitamin D: Immune Health, Levels, and Intake 

While there is no global consensus on optimal serum vitamin D levels [8-10], several organizations have recommendations:

  • National committees tend to be conservative in their recommendations [8]. In the U.S., the National Academy of Medicine (NAM) (previously the Institute of Medicine (IOM)) recommends keeping vitamin D (25(OH)D) levels consistently above 50 nmol/L (20 ng/mL) [11, 12].
  • Other groups have identified higher target vitamin D levels:
    • The American Association of Clinical Endocrinologists (AACE) considers the adequate level for vitamin D to be 75-125 nmol/L (30-50 ng/mL) [2].
    • The International Osteoporosis Foundation (IOF) considers an adequate vitamin D level to be 75-110 nmol/L (30-44 ng/mL) and recommends a minimum target for bone health of 50 nmol/L (20 mg/mL) for all ages [3].
  • The American Geriatrics Society (AGS) working group recommends a minimum goal for 25(OH)D levels in older adults (age 65 and older) of 75 nmol/L (30 ng/mL) [1, 13].
    • Other experts suggest that optimal vitamin D levels are 125 nmol/L (50 ng/mL) [14], or between 100-150 nmol/L (40-60 ng/mL) [8, 15].

The Institute of Medicine recommends a dietary intake of Vitamin D of 600 IU (15 mcg)/day for all ages over 1 year (and for pregnant and lactating women), with increases to 800 IU (20 mcg)/day for individuals over 71 years. 21

Food sources of vitamin D include fatty fish (salmon, mackerel, sardines, cod liver oil) and some types of mushrooms (Shiitake), especially if sundried, contain cholecalciferol (vitamin D3). Because vitamin D not easily obtained from food, many countries, including the US and Canada, encourage the fortification of commonly consumed foods, such as milk, orange juice, other dairy products and cereals with vitamin D. Many people have inadequate sun exposure to meet vitamin D requirements and few people are able to obtain enough vitamin D from food sources alone, therefore supplementation is important. How much to supplement is less clear and will vary based on vitamin D status. Deficient and insufficient individuals will need a different supplemental strategy than those who are not. There is no agreed upon dose globally, recommendations often range from 400-2000 IU (10-50 mcg)/day and your doctor may recommend more. However, a common dose of 1000 IU (25 mcg) of vitamin D3, has been identified to be safe and beneficial for health. 22

The most recognized roles for vitamin D in supporting a healthy immune system include reinforcing the barrier provided by epithelial cells (like skin cells), enhancing the cell’s ability to produce vitamin D at the site of infection, increasing other key defenses of innate immunity and decreasing inflammatory markers. At the site of infection vitamin D has antibacterial and antiviral benefits.12-14 Vitamin D influences some of the genes involved in the innate and adaptive immune systems and in inflammation and therefore affects susceptibility to and severity of bacterial and viral infections. 15,16

The immune system has two parts that overlap, adaptive and innate. Innate immunity is the human body’s first defense against infection. It includes physical barriers including the skin, mucus and lining of the lungs and intestines, as well as cells with receptors that quickly recognize pathogens. The adaptive immune system fights against pathogens or antigens very specifically, but it takes longer to develop. It is activated by exposure to pathogens. 17,18

Observational studies report consistent independent associations between low serum concentrations (amount in the blood) of 25-hydroxyvitamin D (the major circulating vitamin D metabolite) and susceptibility to acute respiratory tract infection. In an analysis of 25 studies, vitamin D supplementation reduced the risk of acute respiratory tract infection among over 11,000 subjects who were supplemented. Daily or weekly supplementation benefited the subjects more than just a large single dose. Those that were most deficient benefited the most. 19

While scientists have not yet determined an exact answer to this question, mechanisms have been proposed. It is known that inflammation and what is called a cytokine storm, which is when an infection triggers your immune system to flood your bloodstream with inflammatory proteins called cytokines, play a critical role in COVID-19 patient outcomes. This dramatic inflammatory reaction can kill tissue and damage organs. Adequate vitamin D levels as well as a healthy balanced diet, particularly the Mediterranean Diet, have been identified as beneficial to offset this inflammatory response. Additionally, vitamin D may exhibit antiviral effects by interfering with viral replication and through its ability to stimulate the immune system and reduce inflammation. 20

Meet The Expert

Michael F. Holick, M.D., Ph.D

Not only was Dr. Michael Holick the first to isolate and identify the active form of vitamin D, but he also played a key role in developing a vitamin D treatment for various conditions including metabolic disease in infants and children as well as patients who were wheelchair bound due to kidney disease.

Helpful Headlines

More news

  1. AGS, American Geriatrics Society (AGS) Consensus Statement: Vitamin D for Prevention of Falls and their Consequences in Older Adults. 2014.
  2. Camacho, P.M., et al., AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS/AMERICAN COLLEGE OF ENDOCRINOLOGY CLINICAL PRACTICE GUIDELINES FOR THE DIAGNOSIS AND TREATMENT OF POSTMENOPAUSAL OSTEOPOROSIS-2020 UPDATE. Endocr Pract, 2020. 26(Suppl 1): p. 1-46.
  3. IOF, Vitamin D recommendations. International Osteoporosis Foundation (IOF). Available online at: https://www.osteoporosis.foundation/health-professionals/prevention/nutrition/vitamin-d. 2024.
  4. Liu, X., A. Baylin, and P.D. Levy, Vitamin D deficiency and insufficiency among US adults: prevalence, predictors and clinical implications. Br J Nutr, 2018. 119(8): p. 928-936.
  5. Elliott, M.E., et al., Fracture risks for women in long-term care: high prevalence of calcaneal osteoporosis and hypovitaminosis D. Pharmacotherapy, 2003. 23(6): p. 702-10.
  6. Feehan, O., et al., Vitamin D deficiency in nursing home residents: a systematic review. Nutr Rev, 2023. 81(7): p. 804-822.
  7. Nair, R. and A. Maseeh, Vitamin D: The “sunshine” vitamin. J Pharmacol Pharmacother, 2012. 3(2): p. 118-26.
  8. Sempos, C.T. and N. Binkley, 25-Hydroxyvitamin D assay standardisation and vitamin D guidelines paralysis. Public Health Nutr, 2020. 23(7): p. 1153-1164.
  9. Pludowski, P., et al., Vitamin D Supplementation: A Review of the Evidence Arguing for a Daily Dose of 2000 International Units (50 µg) of Vitamin D for Adults in the General Population. Nutrients, 2024. 16(3): p. 391.
  10. Sassi, F., C. Tamone, and P. D’Amelio, Vitamin D: Nutrient, Hormone, and Immunomodulator. Nutrients, 2018. 10(11).
  11. Rosen, C.J., et al., IOM committee members respond to Endocrine Society vitamin D guideline. J Clin Endocrinol Metab, 2012. 97(4): p. 1146-52.
  12. Institute of Medicine Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, Dietary Reference Intakes for Calcium and Vitamin D. The National Academies Collection: Reports funded by National Institutes of Health, A.C. Ross, et al., Editors. 2011, National Academies Press (US), National Academy of Sciences.: Washington (DC).
  13. AGS, Recommendations abstracted from the American Geriatrics Society (AGS) Consensus Statement on vitamin D for Prevention of Falls and Their Consequences. J Am Geriatr Soc, 2014. 62(1): p. 147-52.
  14. Cannell, J. Vitamin D Test. Vitamin D Council Blog. Available online at: https://yippy.green/topic/vitamin-d-test (Accessed July 17, 2024). 2024.
  15. Vitamin D Society. Vitamin D Health Benefits. Available online at: https://www.vitamindsociety.org/benefits.php (Accessed July 17, 2024). 2024.
  16. Holick, M.F., et al., Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab, 2011. 96(7): p. 1911-30.
  17. Demay, M.B., et al., Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab, 2024.
  18. Amrein, K., et al., Vitamin D deficiency 2.0: an update on the current status worldwide. Eur J Clin Nutr, 2020. 74(11): p. 1498-1513.
  19. MacLaughlin, J. and M.F. Holick, Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest, 1985. 76(4): p. 1536-8.
  20. Sizar, O., et al., Vitamin D Deficiency. [Updated 2023 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan. Available online at: https://www.ncbi.nlm.nih.gov/books/NBK532266/ (Accessed Aug. 02, 2024). 2023.
  21. Wacker, M. and M.F. Holick, Vitamin D – effects on skeletal and extraskeletal health and the need for supplementation. Nutrients, 2013. 5(1): p. 111-48.
  22. Mandal, A.K.J., et al., Vitamin D status and COVID-19 in older adults. Aging Clin Exp Res, 2020. 32(11): p. 2425-2426.
  23. Prietl, B., et al., Vitamin D and immune function. Nutrients, 2013. 5(7): p. 2502-21.
  24. Herrick, K.A., et al., Vitamin D status in the United States, 2011-2014. Am J Clin Nutr, 2019. 110(1): p. 150-157.
  25. Ramasamy, I., Vitamin D Metabolism and Guidelines for Vitamin D Supplementation. Clin Biochem Rev, 2020. 41(3): p. 103-126.
  26. Riccio, P., Vitamin D, the Sunshine Molecule That Makes Us Strong: What Does Its Current Global Deficiency Imply? Nutrients, 2024. 16(13).
  27. Holick, M.F., Vitamin D and bone health: What vitamin D can and cannot do. Adv Food Nutr Res, 2024. 109: p. 43-66.
  28. Labcorp Testing. Vitamin D. Available online at: https://www.labcorp.com/tests/related-documents/L6851 (Accessed Aug. 23, 2024).
  29. MayoClinic Testing, Vitamin D. Available online at: https://www.mayocliniclabs.com/test-catalog/overview/83670#Clinical-and-Interpretive (Accessed Aug. 23, 2024).
  30. Quest Testing. Vitamin D. Available online at: https://www.questdiagnostics.com/healthcare-professionals/clinical-education-center/faq/faq199 (Accessed Aug. 23, 2024).
  31. Camacho, P.M., et al., AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS AND AMERICAN COLLEGE OF ENDOCRINOLOGY CLINICAL PRACTICE GUIDELINES FOR THE DIAGNOSIS AND TREATMENT OF POSTMENOPAUSAL OSTEOPOROSIS – 2016. Endocr Pract, 2016. 22(Suppl 4): p. 1-42.
  32. Holick, M.F., The vitamin D deficiency pandemic: a forgotten hormone important for health. Public health reviews, 2010. 32: p. 267-283.
  33. Kennel, K.A., M.T. Drake, and D.L. Hurley, Vitamin D deficiency in adults: when to test and how to treat. Mayo Clin Proc, 2010. 85(8): p. 752-7; quiz 757-8.
  34. Gröber, U., et al., Vitamin D: Update 2013: From rickets prophylaxis to general preventive healthcare. Dermatoendocrinol, 2013. 5(3): p. 331-47.
  35. Williams, J.A., et al., Low 25-hydroxyvitamin D concentrations predict incident depression in well-functioning older adults: the health, aging, and body composition study. J Gerontol A Biol Sci Med Sci, 2015. 70(6): p. 757-63.
  36. Ross, A.C., et al., The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: what clinicians need to know. J Clin Endocrinol Metab, 2011. 96(1): p. 53-8.
  37. Heaney, R.P., et al., Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr, 2003. 77(1): p. 204-10.
  38. Giustina, A., et al., Vitamin D in the older population: a consensus statement. Endocrine, 2023. 79(1): p. 31-44.

Disclaimer

Information on this website should not be considered medical advice for COVID-19 or any other illness.  If you are concerned that you may have COVID-19 or other serious illness, you should contact your healthcare practitioner immediately.  Always talk to your healthcare practitioner about any dietary supplements you are taking or plan to take.  Click here to learn more about the content on this website.

Adaptive Immunity

Vatsal Thakkar

How does vitamin D
benefit the immune system?
What is innate and
adaptive immunity?
What is the impact of vitamin D
on respiratory infections?
What role does vitamin D
play in COVID-19?
What intake of vitamin D
is recommended?
What blood levels of vitamin D
should you maintain?

The most recognized roles for vitamin D in supporting a healthy immune system include reinforcing the barrier provided by epithelial cells (like skin cells), enhancing the cell’s ability to produce vitamin D at the site of infection, increasing other key defenses of innate immunity and decreasing inflammatory markers. At the site of infection vitamin D has antibacterial and antiviral benefits.12-14 Vitamin D influences some of the genes involved in the innate and adaptive immune systems and in inflammation and therefore affects susceptibility to and severity of bacterial and viral infections.

The immune system has two parts that overlap, adaptive and innate. Innate immunity is the human body’s first defense against infection. It includes physical barriers including the skin, mucus and lining of the lungs and intestines, as well as cells with receptors that quickly recognize pathogens. The adaptive immune system fights against pathogens or antigens very specifically, but it takes longer to develop. It is activated by exposure to pathogens. 17,18

Observational studies report consistent independent associations between low serum concentrations (amount in the blood) of 25-hydroxyvitamin D (the major circulating vitamin D metabolite) and susceptibility to acute respiratory tract infection. In an analysis of 25 studies, vitamin D supplementation reduced the risk of acute respiratory tract infection among over 11,000 subjects who were supplemented. Daily or weekly supplementation benefited the subjects more than just a large single dose. Those that were most deficient benefited the most. 19

While scientists have not yet determined an exact answer to this question, mechanisms have been proposed. It is known that inflammation and what is called a cytokine storm, which is when an infection triggers your immune system to flood your bloodstream with inflammatory proteins called cytokines, play a critical role in COVID-19 patient outcomes. This dramatic inflammatory reaction can kill tissue and damage organs. Adequate vitamin D levels as well as a healthy balanced diet, particularly the Mediterranean Diet, have been identified as beneficial to offset this inflammatory response. Additionally, vitamin D may exhibit antiviral effects by interfering with viral replication and through its ability to stimulate the immune system and reduce inflammation. 20

The Institute of Medicine recommends a dietary intake of Vitamin D of 600 IU (15 mcg)/day for all ages over 1 year (and for pregnant and lactating women), with increases to 800 IU (20 mcg)/day for individuals over 71 years. 21

Food sources of vitamin D include fatty fish (salmon, mackerel, sardines, cod liver oil) and some types of mushrooms (Shiitake), especially if sundried, contain cholecalciferol (vitamin D3). Because vitamin D not easily obtained from food, many countries, including the US and Canada, encourage the fortification of commonly consumed foods, such as milk, orange juice, other dairy products and cereals with vitamin D. Many people have inadequate sun exposure to meet vitamin D requirements and few people are able to obtain enough vitamin D from food sources alone, therefore supplementation is important. How much to supplement is less clear and will vary based on vitamin D status. Deficient and insufficient individuals will need a different supplemental strategy than those who are not. There is no agreed upon dose globally, recommendations often range from 400-2000 IU (10-50 mcg)/day and your doctor may recommend more. However, a common dose of 1000 IU (25 mcg) of vitamin D3, has been identified to be safe and beneficial for health. 22

While there is no global consensus on optimal serum vitamin D levels, the Institute of Medicine recommends keeping levels consistently above 50 nmol/L (20 ng/mL)23, and the Endocrine Society Clinical Practice Guidelines recommend maintaining blood levels of 25(OH)D consistently above 75 nmol/L (30 ng/ml). 24 Some research indicates that a daily vitamin D dose of 800 IU (20 mcg) can achieve a target 25(OH)D level of at least 50 nmol/L (or 20 ng/mL) in most healthy individuals, and 2000 IU (50 mcg) is sufficient to achieve a level of at least 75 nmol/L (or 30 ng/mL).25

To convert IU to mcg or mg, the Council for Responsible Nutrition offers a conversion calculator at
www.belabelwise.org/conversion-calculator.