What's UP Doc? Is a monthly column where we feature a patient question along with a response from a member of the UPA Scientific Advisory Board.
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Thank you to Dr. Sioban Keel who wrote a detailed response to this question, submitted by a patient member.
Thanks for this question. Vitamin D deficiency is associated with osteoporosis and some other findings. Vitamin D is a fat soluble vitamin and it is not naturally found in many foods. Vitamin D content of some seafood is high. Here is a link to the Dietary Guidelines of American that lists some Vitamin D dense food sources:
The major source of vitamin D for people is not from the diet. It is from its synthesis in the skin. In the skin, something called 7-dehydrocholesterol is converted to vitamin D (specifically, cholecalciferol or vitamin D3) by exposure to UV light. As patients with protoporphyria are forced to avoid sunlight to prevent phototoxic reactions, there is increased prevalence of vitamin D deficiency in protoporphyria patients.
To understand how your medical provider tests for vitamin D deficiency, you need to know that in a person, Vitamin D3 is converted enzymatically in the liver to 25-hydroxyvitamin D, the major circulating form of vitamin D, and then in the kidney to 1,25-dihydroxyvitamin D, the active form of vitamin D.
The form of vitamin D that is measured in the doctor’s office is most commonly, 25-hydoxyvitamin D.
Many experts agree that 25-hydroxyvitamin D levels below 20 ng/mL are suboptimal for bone health.
Vitamin D deficiency can be treated with supplementation. Multiple preparations of vitamin D and its metabolites are available for the treatment of vitamin D deficiency and there is debate around which formulation is optimal for supplementation. The two most commonly available forms of vitamin D supplements are cholecalciferol (aka vitamin D3) and ergocalciferol (aka vitamin D2). The amount of vitamin D required to treat vitamin D deficiency depends in part on a person’s starting level and their ability to absorb the supplement.
Evidence-based consensus guidelines for the diagnosis and management of EPP and XLP (Dickey AK et al. J Am Acad Dermatol 2022) recommend routine screening for vitamin D deficiency and supplementation as per population guidelines.
We encourage protoporphyria patients to talk to their primary care provider about vitamin D and other measures to maintain bone health (including calcium intake and weight-bearing exercise).
Sioban Keel, MD
Associate Professor of Medicine
Division of Hematology
University of Washington