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Vitamin D numbers: what they really mean

Testing your patients for vitamin D1,2

Many physicians recognize the importance of testing vitamin D levels in their high-risk patients, such as older adults and those who are dark-skinned or receive little or no sun exposure. Patients with low vitamin D levels are at risk of osteoporosis and cardiovascular disease, as well as cancer and respiratory disease. Patients who are pregnant or lactating should be tested too, since they represent another high-risk group. Deficiency in pregnancy can lead to preeclampsia, and deficiency while lactating can cause rickets in infants.

An important part of the testing process is advising patients on their vitamin D supplementation needs based on their test results. Here’s what you need to know.

What do vitamin D tests measure?1,2

Vitamin D tests, which include immunoassays and liquid chromatography-mass spectrometry LC/MS/MS, measure the level of 25(OH)D, the main form of circulating vitamin D.

Optimal levels

Vitamin D levels of 30 to 100 ng/mL are considered optimal.

Low levels—suboptimal

Vitamin D levels between 20 and 29 ng/mL are considered suboptimal. Vitamin D insufficiency may lead to elevated parathyroid hormone (PTH) levels (secondary hyperparathyroidism).

Low levels—deficiency

Vitamin D levels <20 ng/mL are considered vitamin D deficient.

Vitamin D deficiency may lead to elevated parathyroid hormone (PTH) levels (secondary hyperparathyroidism).

If your patients' test results reveal that they are vitamin D deficient, the Endocrine Society recommends that they receive vitamin D supplementation. (See the chart below.)

Additional considerations

Monitor serum calcium levels in order to prevent hypercalcemia in patients with
extrarenal production of 1,25(OH)D and in those with primary hyperparathyroidism.

Recommendations for supplementation in vitamin D-deficient patients1

Supplementation in vitamin D-deficient patients depends on your patient's age and medical history. Use this table as a guide to help you advise your patients on recommendations for supplementation:

Recommendations for supplementation in Vitamin D-deficient patients

  Daily Weekly Maintenance*

Infants and toddlers
(0-1 year)

2,000 IU
(for 6 weeks)

50,000 IU
(for 6 weeks)

400-1,000 IU/day

(1 to 18 years)

2,000 IU
(for at least 6 weeks)

50,000 IU
(for at least 6 weeks)

600-1,000 IU/day


6,000 IU
(for 8 weeks)

50,000 IU
(for 8 weeks)

1,500-2,000 IU/day

Obese Patients / Patients with malabsorbtion syndromes / Patiens taking certain medications

6,000-10,000 IU


3,000-6,000 IU/day

*After achieving 25(OH)D levels >30 ng/mL.

Specific supplementation guidelines are not available for pregnant and lactating women. Both groups should be advised to supplement if tests show low levels of vitamin D.

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  1. Holick M, Binkley N, Bischoff-Ferrari H, et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011;96(7):1911-1930.
  2. Khan Q, Fabian C. How I treat vitamin D deficiency. JOP. 2010;6(2):97-101.