Genova Diagnostics Blog

Exploring Health and Healing with Laboratory Testing


How Much Vitamin D?

Question: How much vitamin D should you take? 
Answer: First find out how much you have.

The new research on the prevalence of vitamin D deficiency and insufficiency in children ages one to 21 was alarming, especially because inadequate vitamin D levels in childhood can increase your risk of many diseases as an adult.1-6 The specifics can be found on several sites, the Wall Street Journal health blog is one (look here for the published abstract).

There are a few important questions you should ask:

Question 1: What vitamin D blood level should you aim for?

    Answer: 30 to 40 ng/mL

Vitamin D from the sunThe study defined vitamin D deficiency as a blood level of less than 15 ng/mL and vitamin D insufficiency as 15 to 29 ng/mL. Yet many researchers would agree that 30 ng/mL is a minimum adequate level; while many clinicians aim for levels as high as 40 to 60 ng/mL. The health benefits associated with vitamin D begin at approximately 30 ng/mL, with the greatest benefits seen at 36 to 40 ng/mL.7-9 There is some debate about a toxic level of vitamin D, but it appears to be somewhere around 100 to 150 ng/mL.7, 10, 11 Toxicity from supplementation is generally expected to be a problem in those taking large doses or in those who already have adequate or high levels of serum 25-hydroxyvitamin D. 

Question 2: How much sunshine or vitamin D supplementation should you use?


1000 IU/day vitamin D,
plus 400 IUs in a multivitamin,
plus 10 to 15 minutes of sun exposure/average/per day
(depending on location).

If testing reveals that your serum vitamin D is low then you have two choices to increase your levels: sunshine or supplements.

Over 90% of the vitamin D we get comes from sun UV exposure.12 Many clinicians recommend that patients go outside several times a week and only use sunscreen on their face, leaving their arms and legs exposed. A short term, whole body, sun exposure is reported to provide the equivalent of 10,000 to 20,000 IU of vitamin D.7, 13 Serum vitamin D levels of 54 to 90 ng/mL have been found in individuals living in sunny climates.13,14

An intake of 1000 IU of vitamin D per day is expected to bring vitamin D blood levels in half the adult population up to 30 ng/mL.8 Levels of 4,000 to 10,000 IU of vitamin D were found to be safe in younger adults.8 In a double-blind, placebo-controlled study, girls ages 10 to 17, were given 14,000 IU per week (2000 IU per day) for 1 year without adverse consequences.15 Ten thousand IU per day, given to adults for up to five months, found no toxic effects.13

But be aware that there is a significant range of tolerance to vitamin D supplementation. The following groups are less efficient at converting sunshine to vitamin D: older adults, those with darker skin, and those who are overweight and obese. Those with impaired renal function may have an inability to convert vitamin D to its active form. In addition, individuals with impaired absorption or digestion, such as those with irritable bowel syndrome or celiac disease, may require higher levels of supplementation. So supplement doses of vitamin D vary significantly between individuals.

An acute toxic dose in adults is not well established. Most studies generally tested tolerance by giving vitamin D supplementation in population studies and then testing reactions. They did not first assess the subjects’ vitamin D levels to see if they needed vitamin D supplementation. The potentially toxic dose is significantly lower for very young children.

Question 3: What tests should you be doing?

    Answer: Serum 25-hydroxyvitamin D

The most frequently used assay for vitamin D assessment is serum 25-hydroxyvitamin D, a combination of both D3 (cholecalciferol) and D2 (ergocalciferol). It is the primary circulating form of vitamin D, a direct precursor of the active form, and the most reliable indicator of its status.16

Two common measurements of 25-hydroxyvitamin D are enzyme-linked immunoassay (EIA)17 or radioimmunoassay (RAI).18 Radioimmunoassay (RIA) is FDA approved and thus the current recommended testing procedure.19, 20 Detection of individual 25(OH)D2 and 25(OH)D3 can currently only be done using LC/MS/MS. Though not FDA approved, this method is accurate when performed by experienced personnel using a validated procedure.20

Great Link at the Beverage Institute for Health & Wellness:
(The Beverage Institute for Health & Wellness is part of The Coca-Cola Company)

  1. Kumar J, Muntner, P., Kaskel, al. Prevalence and Associations of 25-Hydroxyvitamin D Deficiency in US Children: NHANES 2001–2004. Pediatrics. Aug. 3, 2009.
  2. Johnson MA, Kimlin MG. Vitamin D, aging, and the 2005 Dietary Guidelines for Americans. Nutr Rev. Sep 2006;64(9):410-421.
  3. Moore CE, Murphy MM, Holick MF. Vitamin D intakes by children and adults in the United States differ among ethnic groups. J Nutr. Oct 2005;135(10):2478-2485.
  4. Heaney RP. The Vitamin D requirement in health and disease. J Steroid Biochem Mol Biol. Oct 2005;97(1-2):13-19.
  5. Calvo MS, Whiting SJ, Barton CN. Vitamin D fortification in the United States and Canada: current status and data needs. Am J Clin Nutr. Dec 2004;80(6 Suppl):1710S-1716S.
  6. Holick MF. The role of vitamin D for bone health and fracture prevention. Curr Osteoporos Rep. Sep 2006;4(3):96-102.
  7. Hollis BW. Circulating 25-hydroxyvitamin D levels indicative of vitamin D sufficiency: implications for establishing a new effective dietary intake recommendation for vitamin D. J Nutr. Feb 2005;135(2):317-322.
  8. Bischoff-Ferrari HA, Giovannucci E, Willett WC, Dietrich T, Dawson-Hughes B. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr. Jul 2006;84(1):18-28.
  9. Vieth R. Why the optimal requirement for Vitamin D(3) is probably much higher than what is officially recommended for adults. J Steroid Biochem Mol Biol. May 2004;89-90:575-579.
  10. Heaney RP, Davies KM, Chen TC, Holick MF, Barger-Lux MJ. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr. Jan 2003;77(1):204-210.
  11. Hollis BW. Symposium: Vitamin D Insufficiency: A significant Risk Factor in Chronic Diseases and Potential Disease-Specific Biomarker of Vitamin D Status. Journal of Nutrition. 2005;135:317-322.
  12. Holick MF. High prevalence of vitamin D inadequacy and implications for health. Mayo Clin Proc. Mar 2006;81(3):353-373.
  13. Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr. May 1999;69(5):842-856.
  14. Arenas-Pinto A, Grant AD, Edwards S, Weller IV. Lactic acidosis in HIV infected patients: a systematic review of published cases. Sex Transm Infect. Aug 2003;79(4):340-343.
  15. El-Hajj Fuleihan G, Nabulsi M, Tamim H, et al. Effect of vitamin D replacement on musculoskeletal parameters in school children: a randomized controlled trial. J Clin Endocrinol Metab. Feb 2006;91(2):405-412.
  16. Mahan K E-SS. Food, Nutrition and Diet Therapy. Vol 1. 11 ed: Saunders; 2000.
  17. Lind C, Chen J, Byrjalsen I. Enzyme immunoassay for measuring 25-hydroxyvitamin D3 in serum. Clin Chem. 1997;43(6 Pt 1):943-949.
  18. Van Laethem JL, Gay F, Franck N, Van Gossum A. Hyperammoniemic coma in a patient with ureterosigmoidostomy and normal liver function. Dig Dis Sci. Nov 1992;37(11):1754-1756.
  19. Diasorin. Liaison 25 OH vitamin D Assay (310900). Sillwater NM 55082 2006.
  20. Hollis BW. Editorial: The Determination of Circulating 25-Hydroxyvitamin D: No Easy Task The Journal of Clinical Endocrinology & Metabolism 2004;89(7):3149-3151.

Comments (4) -

After reading Dr. Joseph Mercola's website, I became interested in the potential for using brief sessions with one of his tanning lamps to keep my vitamin D levels, as well as those of my family members, up during vitamin D "Winter." (I'm a Caucasian living in lower NY state).

Would this investment be worthwhile or would the older members in my family not receive much benefit due to lowered efficiency at converting 7-dehydrocholesterol to cholecalciferol via UVB?

I have been hesitant to invest until I can be a bit more certain that it would benefit all of my family as opposed to just the younger members.

Any input would be appreciated.


Tanning beds have certainly been shown to result in increased vitamin D levels. Tangpricha, et al. concluded that regular users (1 time/wk for 6 mo. or more) of tanning beds that emit ultraviolet B radiation (290–315 nm) increase 25-hydroxyvitamin D concentrations. The study was done on adults 18 to 70 years old. They did not breakdown the response by age, but I would assume that it is like sunlight, it is just less effective in older adults. You could work on getting good sun exposure during summer months, and supplement over the winter.  Whatever route you take, remember to start by checking your, and your family members’, vitamin D levels.

(Tanning is associated with optimal vitamin D status (serum 25-hydroxyvitamin D concentration) and higher bone mineral density, American Journal of Clinical Nutrition, Vol. 80, No. 6, 1645-1649, December 2004.)


But there is a positive correlation between increasing use of tanning beds and the incidence of skin cancer in humans, according to WHO

Is the vitamin D/tanning bed connection akin to the positive correlation between high fructose corn syrup and obesity? Probably not, because there is nothing redeeming about HFCS, whereas a tanning bed, while increasing the potential for skin cancer, can at least give you a shot of cancer-protecting vitamin D first. But then like a lover, it betrays you!


I am genuinely pleased to discover these web site posts which convey such wealth of useful insights. Thanks for giving so much to your audience.


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