Your Questions about Vitamin D, Answered!
Q. Who should have vitamin D blood tests?
A. Presently, it is not recommended that all individuals have annual vitamin blood tests. However, it is appropriate for certain subsets of the population to have routine assessment of vitamin D levels. It is appropriate to determine vitamin D levels in the following individuals:
• Pregnant women
• Infants who are exclusively breastfed
• Individuals with autoimmune diseases
• Individuals with allergic disorders
• Individuals with asthma
• Individuals with immunodeficiency
• Individuals who have very little sun exposure
• Individuals who cover their skin year-round
• Individuals with dark skin
• Individuals who are obese
• Individuals who are ≥ 70 years old
• Individuals who have gut malabsorption syndromes
• Individuals who have risk factors for developing cancer
• Individuals who live north of the 37th parallel
Q. How often should vitamin D levels be checked?
A. An annual baseline vitamin D level is considered to be appropriate for the above individuals. If the vitamin D level is low, then a vitamin D supplement should be started and the vitamin D level should be re-checked in 6 to 8 weeks. If the vitamin D blood level has risen to normal, then the vitamin D supplementation should be continued with annual or semi-annual assessment of vitamin D levels.
Q. What is considered to be an optimal vitamin D level?
A. The current parameters defining “normal” vitamin D levels are based on maintaining normal calcium-bone-phosphate homeostasis. There is no universal agreement on what vitamin D levels are ideal in all individuals in all age brackets. The most commonly accepted vitamin D level parameters used by most reference laboratories in the United States are those developed by the Endocrine Society. Whether these cut points represent vitamin D levels for optimal immunomodulatory, antimicrobial, and paracrine function is unknown at this time and is an area being intensively researched. The Endocrine Society has defined the following serum vitamin D-25-hydroxy parameters:
• 0 – 19 ng/mL (deficiency)
• 20 – 29 ng/mL (insufficiency)
• 30 – 100 ng/mL (sufficiency)
1) Holick, MF et al. Endocrine Society. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab, 2011; 96(7): 1911-1930.
2) Holick, MF. Vitamin D and health: Evolution, biologic functions, and recommended dietary intakes of vitamin D. In Vitamin D: Physiology, molecular biology, and clinical applications. By Holick, MF. Humana Press, 2010.
3) Plum, LA and Deluca, HF. The functional metabolism and molecular biology of vitamin D action. In Vitamin D: Physiology, molecular biology, and clinical applications. By Holick, MF. Humana Press, 2010.
4) Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
5) Bjelakovic, G et al. Vitamin D supplementation for prevention of mortality in adults. Cochrane Database Syst. Rev. 2011 July 6; (7): CD007470.doi:10.1002/14651858.CD007470.pub2.