Vitamin D; Why? How? Where? And How Much?

Alan Cook DC

EasyWebCE - Vitamin D; Why? How? Where? And How Much?

Don’t eat anything that your great-great grandmother wouldn’t recognize as food.

~ Michael Pollan                          

Many questions can be asked about vitamins. A Google search for this term will yield a dizzying number of products, claims, facts, and folly.

Four questions for a provider germane to treating patients are:

  1. Why is a vitamin important?
  2. How does it work?
  3. Where do we get it?
  4. How much do we need?

The following will answer these questions for vitamin D.

In the absence of adequate vitamin D, none of our body systems work well. Vitamin D is needed by all cells.

A cell receives a signal for a demand. In order for the cell to manufacture a given compound to respond, the cell will absorb some 25-hydroxycholecalciferol (vitamin D3) from the bloodstream, and activate this to 1,25-dihydroxcholecalciferol. The activated form, a hormone, is the key to unlock the needed information from the intracellular DNA and, in turn, allows for the proper cellular response.(1) This is the basic process for any and all cell types.

In all of the above, vitamin D is not the cause, but instead enables the cells’ action. Only with adequate levels of extracellular vitamin D (typically in the form of 25-hydroxycholecalciferol) will the cell be able to synthesize the active form in order to properly respond to the stimulus.

In essentially all studies, in all nations, irrespective of latitude, show that the majority of the world’s population has inadequate vitamin D status.(2-6) This deficiency will manifest itself differently, depending upon the tissue being stressed.

The list of diseases seen with poor vitamin D status is diverse and long. The partial list includes: osteoporosis, osteomalacia, rickets, hypertension, cardiac disease, prematurity and/or low birth weight, diabetes and metabolic syndrome, periodontal disease, increased susceptibility to infection, various cancers, multiple sclerosis, influenza, depression, and schizophrenia.(7-18)

Where do we get it?

There are several sources of vitamin D: food, sunshine, and supplements. The below chart has several surprises. Note the dramatic difference between farmed vs. wild caught salmon or eggs raised from chickens who live indoor vs. outdoor. (19)

Vitamin D Chart 01

Most of the food with significant cholecalciferol, vitamin D3, are flesh-based. The major exception is mushrooms. Mushrooms are a source of ergocalciferol; vitamin D2.

When fresh button mushrooms are deliberately exposed to midday sunlight for 15–120 min, they generate significant amounts of vitamin D2, approaching the daily requirement of vitamin D recommended. However, the amount of vitamin D2 generated depends on the time of day, season, latitude, weather conditions, and exposure time. Slicing the mushrooms prior to sun exposure significantly increases the D2 synthesis.(20)

Vitamin D - Sunny day with woman

How much do we need?

Various political bodies within medicine have made recommendations as to daily intake and the proper blood levels of vitamin D. The Food and Nutrition Board suggest the least intake. Their recommendations become those of the United States government and are therefore, influential.

The Endocrine Society weighs in for two reasons; the activated form of vitamin D is a hormone and the Society is highly involved in bone metabolism and diseases such as osteoporosis. Their recommendations are significantly higher than those of the Food and Nutrition Board.

The vitamin D Council is made up of researchers that are designing and performing many of the clinical trials for vitamin D. The intakes that they are suggesting are 2-6 fold as compared with the Food and Nutrition Board. I consider their recommendations to be far more credible and sophisticated in their nuance.

Vitamin D Chart 02

The various organizations are recommending food intakes but what’s most important is total intake; food plus sunshine plus supplements. These are fine for guidelines however, the blood levels of 25-hydroxycholecalciferol can be measured which yields an essential finding.

The following are the most common laboratory thresholds used in the United States when measuring 25-hydroxycholecalciferol, the storage form of vitamin D.

25-hydroxycholecalciferol (21)

normal ›30 ng/ml
insufficiency 20-30 ng/ml
deficiency ‹20 ng/ml

When looking at the blood levels of non-westernized societies (e.g. Masai tribe), it’s common to see a level of 60 ng/ml.(22) Many vitamin D researchers suggest that optimal levels should be 45-50 ng/ml. These are substantially higher than the 30 ng/ml threshold reported as normal.

In the United States, the mean level of 25-hydroxycholecalciferol in white adults is 26 ng/ml. There is some seasonal variability here. The mean level for Hispanics is 21 and for African-Americans it is 16. All of these are below the 30 ng/ml threshold. This is consistent with findings of deficiency of various ethnic groups across several studies. For example, Afro-Americans have the most vitamin D deficiency (estimated at 82%), Hispanics at 70%, while the US population at large has a reported 42% deficiency.(23)

There is one other factor adding to the widespread deficiency. As the populations average weight increases, more vitamin D is needed to combat the “dilution” of this nutrient. Vitamin D is fat soluble and gets incorporated into body fat. Obese patients need 2-3x more vitamin D, from whatever source, as compared with people at their proper body weight.(24)

The question of how much to recommend persists. Several vitamin D researchers suggest that adult daily intake should be approximately 4000-6000 IU from all sources; sunshine, food, supplements. If someone works and lives indoors and does not eat fish regularly, then a supplement of 4000-6000 IU/day is reasonable.(25)

However, if the patient has a blood level of 30 ng/ml and you are trying to bring them up to 45, you would need an additional 1500 IUs per day. Serum 25-hydroxycholecalciferol rises 1 ng/ml for every 100 additional IUs of vitamin D3 be it from sunshine, food, or supplements.(25)

This formula is an approximation as the patient’s weight is another important variable. The more they weigh, the more additional D3 is needed. After increasing the vitamin D intake, blood levels should be retested 12-16 weeks later.


In conclusion, vitamin D is a necessary nutrient that impacts multiple organ systems. The notion that vitamin D is only bone-active is antiquated. Vitamin D can be acquired through the diet; mostly fish, liver, or fortified foods or via ultraviolet B that strikes skin. Absorption rates, both from the diet or the sun, are highly variable. Vitamin D has been demonstrated to prevent and/or treat, or partially treat, a growing variety of common diseases. In order to know how much vitamin D to prescribe, the best first step is to test for 25-hydroxycholecalciferol. The optimal level is not fully agreed upon however, a substantial number of researchers and expert panels put this at 45-60 ng/ml, which is higher than the current prevailing opinion of 30 ng/ml.

Serum 25-hydroxycholecalciferol levels below 32 ng/ml are not adequate for any body system. Optimal levels can be accomplished with sunshine, dietary intake, or supplements without approaching a level that anyone who is informed would consider toxic. Inputs from all sources combined needed to sustain optimal levels are in the range of 5000 IU/day. This is far higher than the current adult RDA of 600 IU.

Alan Cook DC has been in practice since 1989.  Currently he is involved in two professional endeavors: Treating patients in a collaborative medical clinic system (Open Door Community Health Center) in Eureka, CA. and EasyWebCE;  providing chiropractic continuing education in a web-based video format.

  1. Bikle DD. Vitamin D metabolism, mechanism of action, and clinical applications. Chem Biol. 2014;21(3):319-329. 
  2. Holick M: High prevalence of vitamin D inadequacy and implications for health. Mayo Clinic Proc 2006, 81:353–373.
  3. Allain TJ, Dhesi J. Hypovitaminosis D in older adults. Gerontology. 2003;49(5):273-278.
  4. O’Malley G, Mulkerrin E. Vitamin D insufficiency: a common and treatable problem in the Irish population. Ir J Med Sci. 2011;180:7-13.
  5. Arunabh S, Pollack S, Yeh J, Aloia JF. Body fat content and 25-hydroxyvitamin D levels in healthy women. J Clin Endocrinol Metab. 2003;88:157-61.
  6. Bandeira F, Griz L, Dreyer P, Eufrazino C, Bandeira C, Freese E. Vitamin D deficiency: a global perspective. Arq Bras Endocrinol Metabol. 2006 Aug;50(4):640-6.
  7. Aranow C. Vitamin D and the immune system. J Investig Med. 2011;59(6):881-886.
  8. Zeitz U, Weber K, Soegiarto DW, Wolf E, Balling R, Erben RG. Impaired insulin secretory capacity in mice lacking a functional vitamin D receptor. Faseb J. 2003;17(3):509-511.
  9. Sigmund CD. Regulation of renin expression and blood pressure by vitamin D(3). J Clin Invest. 2002;110(2):155-156. 
  10. Wagner CL, Greer FR, American Academy of Pediatrics Section on B, American Academy of Pediatrics Committee on N. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics. 2008;122(5):1142-1152.
  11. Jones AN, Hansen KE. Recognizing the musculoskeletal manifestations of vitamin D deficiency. J Musculoskelet Med. 2009;26(10):389-396.
  12. Plotnikoff GA, Quigley JM. Prevalence of severe hypovitaminosis D in patients with persistent, nonspecific musculoskeletal pain. Mayo Clin Proc. 2003;78(12):1463-1470. 
  13. Al-Khalidi B, Kimball SM, Rotondi MA, Ardern CI. Standardized serum 25-hydroxyvitamin D concentrations are inversely associated with cardiometabolic disease in US adults: a cross-sectional analysis of NHANES, 2001-2010. Nutr J. 2017;16(1):16.
  14. Cannell JJ, Vieth R, Umhau JC, et. al. Epidemic Influenza and Vitamin D. Cambridge University Press (online); 07 Sep 2006.
  15. Aloia JF, Li-Ng M. Epidemic Influenza and Vitamin D. Epidemiology and Infection. 2007; 135: 1095-8.
  16. Urashima M, Segawa T, Okazaki M, et. al. Randomized Trial of Vitamin D Supplementation to Prevent Seasonal Influenza A in Schoolchildren. Am J Clin Nutr. 2010; 91: 1255-60.
  17. Hoang MTT, DeFina LF, Willis BL, et. al. Association Between Low Serum 25-hydroxyvitamin D and Depression in a Large Sample of Healthy Adults: the Cooper Center Longitudinal Study. Mayo Clinic Pro 1986; 86: 1050-55.
  18. Vitamin D and Depressioin: A Systematic Review and Meta-analysis Comparing Studies With and Without Biological Flaws. Nutrients 2014; 6: 1501-18.
  19. USDA Food Data Central
  20. Keegan RJH, Lu Z, Boqusz JM, Williams JE, Holick MF. Photobiology of vitamin D in mushrooms and its bioavailability in humans. Dermatoendocrinol 2013;5:165-76.+
  21. Holick MF. Vitamin D Status: Measurement, Interpretation, and Clinical Application. Ann Epidemiol. 2009;19:73-8.
  22. Luxwolda MF, Kuipers RS, Kema IP, Dijck-Brouwer DA, Muskiet FA. Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l. Br J Nutr. 2012;108:1557-61.
  23. Hanley DA, Davison KS. Vitamin D Insufficiency in North America. J Nutr. 2005;135:332-7.
  24. Gallagher JC, Yalamanchili V, Smith LM. The effect of vitamin D supplementation on serum 25(OH)D in thin and obese women. J Steroid Biochem Mol Biol. 2013;136:195-200. 
  25. Heaney RP. Vitamin D in Health and Disease. Clin J Am Soc Nephrol. 2008;3:1535-4