Vitamin D, Covid, and Skin Color

What are the recommended Vitamin D levels?

Medical organizations, including the National Academy of Medicine in the US, the Endocrine Society, and others have developed recommendations for both the recommended daily intake of Vitamin D, as well as ideal levels to have circulating in the blood [1-10].  An important caveat to these recommendations is that they assume zero Vitamin D synthesis from the sun.  Since the sun is historically the main way that humans have obtained Vitamin D [11] (with the exception of Arctic peoples [12]), it doesn’t really make a lot of sense to think of Vitamin D requirements in terms of intake through food or supplements.  Nevertheless, experts have made some recommendations concerning Vitamin D uptake and Vitamin D levels in the blood.

There are a few different ways in which recommended Vitamin D levels are shown, which can get confusing.  Some recommendations are shown in terms of target blood concentrations, whereas others are expressed in term of how much should be taken in supplements.  Additionally, blood Vitamin D levels can be shown as ng/liter or nmol/liter, whereas recommended dosages for intake can be shown as nanograms (ng) micrograms (mcg), International Units (IU), or a percentage of recommended Daily Allowance (% RDA; RDA generated by National Academy of Medicine).  Here are some tables to help you make sense of all these numbers.  As you can see, experts mostly agree on ideal levels of Vitamin D in the blood, but disagree on how much Vitamin D supplementation is needed to achieve those levels.  This disagreement is perhaps not too surprising considering that most of our Vitamin D comes from the sun’s action on our skin, and not from food. 

Factors that increase the amount of Vitamin D intake needed to achieve desired blood concentrations

  • dark skin (blocks UV-B rays needed for Vitamin D synthesis in deeper skin layers [more info])
  • lack of sun exposure (eg during winter)
  • increased age (changes in the skin and kidney reduce the ability of the body to manufacture Vitamin D from the sun, although intake from food/supplementation is unaffected [7,13,14])
  • pregnancy (healthy fetal development requires substantial Vitamin D, and will deplete maternal supplies [7,15,16])
  • obesity (because Vitamin D is fat-soluble, it becomes sequestered in fat and unavailable in blood for cells that need it [7,17-20])

 

 

Recommended Vitamin D levels in Blood

Source of Recommendation Target Blood Concentration
(ng/liter)		 Target Blood Concentration
(nmol/liter)
     
National Academy of Medicine [5,6] 30-60 ng/liter 50-125 nmol/liter
Endocrine Society [7,8] 30-60 ng/liter 75-150 nmol/liter
Recommended Target Blood Concentrations
 note: 1 ng = 2.5 nmol (for Vitamin D3)

 

Recommended Levels of Intake

Source of Recomendation Recommended Daily Intake
(IU/day)		 Recommended Daily Intake
(mcg/day)
     
National Academy of Medicine [5,6]    
0-12 months 400 IU 10 mcg
1-70 years 600 IU 15 mcg
over 70 years 800 IU 20 mcg
     
Endocrine Society [7,8]    
0-12 months 400-1000 IU 10-25 mcg
1-18 years 600-1000 IU 15-25 mcg
over 19 years 1500-2000 IU 38-50 mcg
obese children, adults double the recommendation  
Recommended Daily Intake
notes:
 1 mcg = 1000 ng
 1 mcg = 40 IU (for Vitamin D3)
 1 IU = 25 ng (for Vitamin D3)

 

 

 

REFERENCES

  1. Torborg, L.  2017.  Mayo Clinic Q and A: How much Vitamin D do I need?  Mayo Clinic News Network.

  2. Tello, M.  2020.  Vitamin D: What’s the “right” level?  Harvard Health Publishing Health Blog.

  3. Harmon, K.  Recommended Daily Vitamin D Intake Gets a Boost.  Scientific American Online. Nov 30, 2010.

  4. Bouillon, R.  2017.  Comparative analysis of nutritional guidelines for vitamin D.  Nature Rev. Endocrinol. 13;466.

  5. National Institutes of Health Office of Dietary Supplements.  Vitamin D Fact Sheet for Consumers. 

  6. National Institutes of Health Office of Dietary Supplements.  Vitamin D Fact Sheet for Health Professionals. 

  7. Holick, M.  et al.  2011.  Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J. Clin. Endocrinol. Metab. 96:1911.

  8. Holick, M.  2007. Vitamin D Deficiency. N. Engl. J. Med. 357:266.

  9. Seaborg, E.  2014.  Just Right: How Much Vitamin D is Enough?  Endocrine Society Endocrine News.

  10. Charoenngam, N., Shirvani,  A., Holick, M.2019.  The ongoing D-lemma of vitamin D supplementation for nonskeletal health and bone health.  Curr. Opin. Endocrinol. Diabetes Obes. 26:301.

  11. Lents, N.  2018.  We Can Thank Poor Evolutionary Design for Vitamin D Deficiencies. Discover Magazine Online.

  12. Luick, B. Bersamin, A., Stern, J.  2014.  Locally harvested foods support serum 25-hydroxyvitamin D sufficiency in an indigenous population of Western Alaska. Int. J. Circumpolar Health.  73: 22732.

  13. MacLaughlin, H. & Holick, M.  1985.  Aging decreases the capacity of human skin to produce vitamin D3. J. Clin. Invest.  76: 1536.

  14. Gallagher, J.  2013.  Vitamin D and aging. Endocrin. Metab. Clin. North. Am.  42: 319.

  15. Bodnar, L. et. al. 2007.  High prevalence of vitamin D insufficiency in black and white pregnant women residing in the northern United States and their neonates. J. Nutr.  137: 447.

  16. Melough, J.  2020.  Maternal Plasma 25-Hydroxyvitamin D during Gestation Is Positively Associated with Neurocognitive Development in Offspring at Age 4-6 Years. J. Nutr.  online ahead of print.

  17. Wortsman, J. et al.  2000.  Decreased bioavailability of vitamin D in obesity. Am. J. Clin. Nutr.  72: 690.

  18. Rajakumar, K. et al.  2011.  Vitamin D status, adiposity, and lipids in black American and Caucasian children. J. Clin. Endocrin. Metab.  96: 1560.

  19. Vimaleswaran, K. et al.  2013.  Causal relationship between obesity and vitamin D status: bi-directional Mendelian randomization analysis of multiple cohorts. PLoS. Med.  10: e1001383.

  20. Ganglodd, A. et al.  2016.  Changes in circulating vitamin D levels with loss of adipose tissue. Curr. Opin. Clin. Nutr. Metab. Care.  19: 464.