Vitamin D Assays
Globally, over 1 billion people are vitamin D deficient,1 and in the United States the NHANES III study from 2001 to 2004 indicated that 77% of U.S. adults are insufficient or deficient. Deficiency of vitamin D rates have increased as people have limited their sun exposure due to the risk of skin cancer. People living near the equator who are exposed to sunlight without sun protection have robust levels of vitamin D; however, vitamin D deficiency is found in regions where skin exposure is limited and where sun protection is promoted to avoid UV injury to skin.
Groups at Higher Risk for Vitamin D Deficiency2
There are several groups at higher risk of vitamin D deficiency including:
- Breastfed Infants: Sufficiency is dependent on the mother’s vitamin D sufficiency level. Mother's milk typically contains about 25 IU/L of vitamin D.
- Older Adults: As people age, the skin is not able to synthesize vitamin D as effectively, and reduced kidney function impacts the ability to convert vitamin D.
- Dark Skinned People: Melanin in darker skin reduces the ability to produce vitamin D from sunlight exposure.
- Limited Sun Exposure: Eliminates one of the two possible sources of vitamin D.
- Obesity: Vitamin D is fat soluble, which does not allow it to circulate as freely.
- Other: Gastric bypass patients have less small intestine available to absorb vitamin D.
Vitamin D Sufficiency Levels
Most experts3,4,5 agree that vitamin D sufficiency is above 30 ng/mL (75 nmol/L), an insufficient level is between 20 and 30 ng/mL (50 to 75 nmol/L), and a deficient level is any value below 20 ng/mL (50 nmol/L).
Vitamin D Supplementation2
Oral vitamin D supplementation has proven to be very effective at raising vitamin D levels. Recommendations vary by subgroup:
1. Holick MF "Vitamin D deficiency". N. Engl. J. Med. (2007) 357 (3): 266–81.
2. Bringhurst FR, et.al., “Bone and Mineral Metabolism in Health and Disease”; Chapter 23 of “Harrison’s Endocrinology”, J. Larry Jameson, editor, McGraw-Hill Medical Publishing Division, copyright 2006.
3. Bischoff-Ferrari HA, et al. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr 2006;84:18-28.
4. Malabanan A, et al. Redefining vitamin D insufficiency. Lancet 1998;351:805-6.
5. Souberbielle JC et al. Vitamin D and musculoskeletal health, cadiovascular disease, autoimmunity and cancer: Recommendations for clinical practice. Autoimmunity Reviews 9 (2010) 709-715.