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Vitamin D is for deficient.

November 29, 2008

Matthew Vasey, MD



Vitamin D is for deficient. Well not really, but since approximately one-sixth of the world's population is deficient or at least insufficient one could make the case. For the purposes of this article when referring to Vitamin D in biochemical terms all of its slight molecular variants i.e. D3, D2 and previtamin forms which are obtained from three major sources, food, supplemental pills, and the sun are included.

How does a vitamin come from the sun? A particular type of fat in the skin undergoes an immediate change to vitamin D thanks to heat energy from a particular type of ultraviolet light. Vitamin D found from food and pill supplements are digested in the stomach and absorbed by the intestines. Sort of like an assembly line, once vitamin D is in your blood it travels through your liver where it gets tweaked to 25-hydroxyvitamin D, the inactive form commonly measured by lab tests, and then tweaked again by your kidneys where it picks up the number one and a comma, creating the active form 1,25-hydroxyvitamin D.

This "Pimp My Vitamin" form of "D" impacts lots of things in the body and in this instance, bone maintenance. It helps regulate the bodies' absorption of bone's building blocks, calcium and phosphorus while also regulating bone's cellular builders and demolishers. It is easy to appreciate the importance of vitamin D in bone health particularly in women as it relates to osteoporosis. There isn't much debate over this or over the influence of "D" on other cellular and disease processes. The issue stems from how much "D" is needed and what is the best way to get it. One encyclopedic type medical textbook on vitamin D even presents chapters that differ in opinion from one another.

Dr. Michael Holick, a very well published researcher and controversial expert on vitamin D emphasizes its important role in chronic medical illnesses, common cancers, infectious diseases, mental health, musculoskeletal health and cardiovascular disease. He references a lot of literature out there showing increased risk of cancer and cancer deaths in direct relation to geographic latitude when compared to lower latitudes; more importantly, a reasonable explanation of how increased vitamin D and sun exposure is associated with lower risk of these cancers.

It is careless to assume vitamin D deficiency doesn't apply to you given that deficiencies have been identified in many populations and even medical students and doctors who were eating appropriately and supplementing their vitamin D inadequately. Studies of small populations in sunny Florida have also yielded percentages of vitamin D deficient adults even when just 5-30 minutes of sun exposure on arms and legs in the mid-day sun twice a week is considered suffient for vitamin D production. Personally, I can say while living in New York City walking a few blocks to and from work every day otherwise venturing out mostly in the evenings that routine screening in the winter months found me to be deficient in vitamin D.

The debate continues over the recommended amount of vitamin D supplementation, how patients should get it, what role tanning beds and unprotected deliberate sun exposure have in vitamin D supplementation given the tradeoff off between a known deadly skin carcinogen (cancer causing agent) and health benefits when compared to "over the counter" and prescribed vitamin supplements with a far lower risk profile. It is very likely that many people reading this are vitamin D deficient. Speak with your doctor about vitamin D, particularly if you are pregnant or breast feeding. Be sure to check with your health insurance company about coverage for vitamin D labwork, as not all will cover the costs.

References:

1. Holick, M. Vitamin D deficiency. N Engl J Med 2007 357(3):266-281.
2. Vitamin D. Second Edition. Edited by David Feldman, Wesley Pike and Francis Glorieux. 1892pp. in two volumes. San Diego, California, Elsevier Academic Press. 2005.
3. Gordon CM, DePeter KC, Feldman HA, Grace E, Emans SJ. Prevalence of vitamin D deficiency among healthy adolescents. Arch Pediatr Adolesc Med 2004;158:531-537.
4. Sullivan SS, Rosen CJ, Halteman WA, Chen TC, Holick MF. Adolescent girls in Maine at risk for vitamin D insufficiency. J Am Diet Assoc 2005;105:971-974.
5. Nesby-O'Dell S, Scanlon KS, Cogswell ME, et al. Hypovitaminosis D prevalence and determinants among African American and white women of reproductive age: Third National Health and Nutrition Examination Survey, 1988-1994. Am J Clin Nutr 2002;76:187-192.
6. Cava R. Correspondence: Vitamin D deficiency. N Engl J Med. Volume 357:1980-1982
7. Tangpricha V, Pearce EN, Chen TC, Holick MF. Vitamin D insufficiency among free-living healthy young adults. Am J Med 2002;112:659-662.
8. Jones G, Dwyer T. Bone mass in prepubertal children: gender differences and the role of physical activity and sunlight exposure. J Clin Endocrinol Metab 1998;83:4274-4279

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