Vitamin D: A Rapid Review

Mark A. Moyad, MD, MPH


Dermatology Nursing. 2009;21(1) 

In This Article

The Vitamin D Blood Test (25-OH Vitamin D): Who, How, When, and Where

Clinically speaking, things began to change in the 1970s when the blood test for vitamin D (known as the "25-OH vitamin D" test) became more accurate and widely utilized (Wolpowitz & Gilchrest, 2006; Zerwekh, 2008). This test reflected the total amount of vitamin D in the body that was coming from all sources (diet, dietary supplements, and the sun), which makes this test extremely important in the field of nutrition. Low concentrations of 25-OH vitamin D causes secondary hyperparathyroidism (high levels of parathyroid hormone or PTH). This means a person loses more calcium from his/her bones when PTH is abnormally high (PTH>65 pg/ml) and has an even greater risk for bone loss. Vitamin D3 seemed more effective than D2 at raising this important blood test. Furthermore, preliminary work showed that enzymes in the liver and the final vitamin D receptors (VDR) in important tissues bind vitamin D3 more effectively. As humans age, these metabolic differences make a very large difference in terms of effectiveness. Almost all successful anti-fracture clinical trials have used vitamin D3 at a dosage of at least 800 IU/day (20 mcg per day).

Ideally, the vitamin D blood test should be offered from the fall season through winter when vitamin D blood levels are at their lowest. Spring and summer months can give patients and clinicians a false sense of vitamin D security. Patients should have a 25-OH vitamin D test yearly from September through March, around the same time they get their fasting lipid level. Fasting is not necessary to obtain a vitamin D level; however, getting blood tests at the same time makes sense, reducing the burden of time on the patient. Some health insurances cover vitamin D testing and some do not, and prices vary from $10 to $50, so local laboratory costs should be checked before telling the patient that a vitamin D test is needed.

An example of the greater need for utilizing the vitamin D blood test are men on androgen or hormone deprivation treatment for prostate cancer or those on this or a similar medication for other medical conditions (such as women being treated for breast cancer). It is now common knowledge that these life-saving medications that reduce estrogen and testosterone can also increase the risk of bone loss. In the author’s opinion, less than 1% of men and women are offered a vitamin D test when given this injection, and this is disappointing. Some of these men and women will be prescribed a bisphosphonate or another drug without hesitation if needed. However, some of these men and women were not given the chance to maintain their bone mineral density through lifestyle changes (such as weight lifting) and supplement intake of calcium and vitamin D before being offered the prescription medication. In other words, health care professionals should offer a cholesterol-lowering drug if diet and exercise do not work (for example, cardiovascular prevention), but patients should be educated about lifestyle changes as well. Therefore, when diet, exercise, and blood tests do not work to maintain bone mineral density, the bisphosphonates and other osteoporosis prevention medications are a wonderful option, and are more effective with diet and exercise.


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