Vitamin D Deficiency

If you live 37 (or more) degrees north of the Equator, you experience such little sunlight that your body can’t synthesize adequate vitamin D from sun exposure alone. That includes anyone north of Atlanta! This isn’t necessarily a bad thing- the American Academy of Dermatology recommends against getting vitamin D from sun exposure given the risk of skin cancer.

Vitamin D naturally occurs in few foods. Humans create their own vitamin D when UV rays hit the skin and trigger the process. Once vitamin D is in our system, whether via the sun or food, it undergoes steps to be transformed into its active form. The liver takes vitamin D and turns it into calcidiol, or 25-hydroxyvitamin D. Then, the kidneys convert calcidiol into calcitriol, or 1,25di-hydroxyvitamin D. 

Certain medical conditions require special consideration in order to ensure adequate vitamin D status. These conditions include chronic kidney disease and malabsorptive conditions such as cystic fibrosis, IBD, celiac disease, and short bowel syndrome.


Chronic Kidney Disease

Vitamin D deficiency (<20 ng/mL) and insufficiency (20-29 ng/mL) are common in individuals with CKD and those on dialysis. If left unaddressed, low serum vitamin D can contribute to secondary and tertiary hyperparathyroidism in this patient population. Kidney Disease Outcome Quality Initiative (KDOQI) recommends vitamin D supplementation to prevent this.1


Malabsorptive Disorders

Vitamin D is a fat-soluble vitamin, meaning it requires the presence of lipids to maximize absorption. Thus, impaired digestion and absorption of fat can contribute to poor vitamin D status in individuals with malabsorption related to conditions like liver disease or Crohn’s disease.2

Vitamin D status can also be impaired in patients without outright fat malabsorption. Since vitamin D is absorbed in the ileum, patients who have undergone gastrointestinal surgery involving the ileum may be at increased risk for deficiency.2

As an RD, what should I recommend?

Of course, encourage your patient or client to meet the RDA for vitamin D through food and/or supplementation, as appropriate. If you suspect that your patient may be deficient in vitamin D, you can recommend that they see their primary care provider for a blood test. Take extra caution when counseling patients with medical conditions that may complicate their vitamin D status.

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Jean Ziegenhorn

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