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Vitamin D.
Article Type:
Report
Subject:
Alfacalcidol (Health aspects)
Alfacalcidol (Physiological aspects)
Calcifediol (Health aspects)
Calcifediol (Physiological aspects)
Vitamin D (Health aspects)
Vitamin D (Physiological aspects)
Authors:
Plaut, David
McLellan, Willilam
Pub Date:
01/01/2011
Publication:
Name: Journal of Continuing Education Topics & Issues Publisher: American Medical Technologists Audience: Academic Format: Magazine/Journal Subject: Education Copyright: COPYRIGHT 2011 American Medical Technologists ISSN: 1522-8606
Issue:
Date: Jan, 2011 Source Volume: 13 Source Issue: 1
Geographic:
Geographic Scope: United States Geographic Code: 1USA United States

Accession Number:
277674931
Full Text:
Introduction

In the past few years, there has been increased interest in the measurement of vitamin D for a number of reasons. It continues to be shown that there is a negative correlation between vitamin D levels in the blood and the number of bone fractures that occur, especially in elderly people. In certain parts of the U.S., and in other parts of the world, cases of rickets still occur. It also appears that the incidence of vitamin D deficiency is increasing. Part of this may be due to urbanization and the increase in smog in those areas as well as less exposure to ultraviolet (UV) radiation.

There is now evidence that vitamin D deficiency is associated with coronary artery disease, internal cancers (skin cancers are different), and multiple sclerosis, type 1 diabetes, tuberculosis, Alzheimer's disease, psoriasis, asthma and rejection of transplanted organs, as well as all-cause mortality. Further, there are now commercial assays for vitamin D that allow testing to be done in smaller institutions.

In this brief review, we summarize the current data on vitamin D in a number of diseases, discuss suggested daily intake of vitamin D as well as calcium and magnesium, and describe current methods used by the clinical laboratory to measure vitamin D.

What is Vitamin D and Why is it Imporant for Us?

Vitamin D is a group of fat-soluble steroids. The term "vitamin D" refers to several different forms of vitamin D. The two forms that are important in humans are ergocalciferol (calcidiol, vitamin [D.sub.2]) and cholecalciferol (calcitriol, vitamin [D.sub.3]). Vitamin D without a subscript refers to either [D.sub.2] or [D.sub.3] or both. Vitamin [D.sub.2] is synthesized by plants; very little is found in humans. Vitamin [D.sub.3] is synthesized by humans in the skin when it is exposed to ultraviolet-B (UV-B) rays from sunlight; it is also available from supplements and occurs naturally in a small range of foods. Foods may be fortified with vitamin [D.sub.2] or [D.sub.3].

Vitamin D can be stored in and then released from fat cells. Vitamin D is carried by vitamin D-binding protein in the bloodstream to the liver, where it is converted into the prohormone, vitamin [D.sub.2]. Circulating calcidiol may then be converted into vitamin [D.sub.3], the biologically active form of vitamin D. This occurs in either the kidneys or by monocyte-macrophages in the immune system. When synthesized by monocyte-macrophages, calcitriol acts locally as a defense against microbial invaders. When synthesized in the kidneys, vitamin [D.sub.3] circulates as a hormone. Vitamin D also modulates neuromuscular function, reduces inflammation, and influences the action of many genes that regulate the proliferation, differentiation and apoptosis of cells. Calcium and phosphorus are also needed for healthy teeth.

Occasionally, drugs used to treat seizures, particularly phenytoin (Dilantin), can interfere with the production of 25-hydroxyvitamin D in the liver.

Vitamin D and Bones

Vitamin D aids in regulating, among other things, the concentration of calcium and phosphate in the bloodstream, promoting the healthy mineralization, growth and remodeling of bone, and the prevention of hypocalcemic tetany. Vitamin D insufficiency can result in thin, brittle, or misshapen bones, while sufficiency prevents rickets in children and osteomalacia in adults, and, together with calcium, helps to protect older adults from osteoporosis. Cranney (1) prepared a meta-analysis of the literature on the value of vitamin D supplements. "The results highlight the need for additional high quality studies in infants, children, premenopausal women, and diverse racial or ethnic groups." Cranney and his team found "fair evidence from studies of an association between circulating vitamin D concentrations with some bone health outcomes (established rickets, falls, and bone mass density [BMD]). In most trials, the effects of vitamin D and calcium could not be separated. Vitamin [D.sub.3] (>700 IU/day) with calcium supplementation compared to placebo has a small beneficial effect on BMD, and reduces the risk of fractures and falls, although benefit may be confined to specific subgroups. Vitamin D intake above current dietary reference intakes has not always been reported to be associated with an increased risk of adverse events.

However, most trials of higher doses of vitamin D were not adequately designed to assess long-term harms."1 As you will see, there is some disagreement regarding this last statement. For example, "Vitamin D toxicity is an issue for people with health problems such as liver or kidney conditions, or if one takes thiazide-type diuretics." (2)

Vitamin D and Coronary Artery Disease

Pilz et al. (3) found that severe vitamin D deficiency was strongly associated with sudden cardiac death, cardiovascular events, and mortality, and there were borderline associations with stroke and fatal infection. In agreeing with this, Kulie stated that "low vitamin D levels are associated with increased overall and cardiovascular mortality." (4) However, Frazer stated that "calcium supplements (without co-administered vitamin D) are associated with an increased risk of myocardial infarction. As calcium supplements are widely used, these modest increases in the risk of cardiovascular disease might translate into a larger burden of disease in the population." (5)

Vitamin D and Cancer

Chung reviewed the literature on vitamin D and cancer and found that "the data were inconsistent across studies for colorectal and prostate cancer. For prostate cancer, some studies reported that high calcium intakes were associated with an increased risk. For breast cancer, calcium intake in premenopausal women was associated with a decreased risk." (6)

Zhou, Stoltsfus and Swam (7) also reviewed data and found three themes: 1) raising the vitamin D levels to sufficient state (32-100 ng/ml) achieved colorectal cancer risk reduction; 2) increasing the intake of vitamin D reduced colorectal cancer risk; and 3) increasing vitamin D intake to 1,000 IU daily is safe and likely sufficient to raise serum vitamin D levels above the 32 ng/ml suggested to achieve colorectal cancer risk reduction.

Vitamin D and Multiple Sclerosis

Pierrot-Deseilligny claimed that "it can no longer be ignored that many multiple sclerosis (MS) patients have a lack of vitamin D, which could be detected and corrected using an appropriate vitamin D supplementation in order to restore their serum level to within the normal range. From a purely medical point of view, vitamin D supplementation appears to be unavoidable in order to improve the general state of these patients. It has been suggested that a reduction in the number of cases of MS could be reduced through vitamin D supplements. Furthermore, it cannot currently be ruled out that this supplementation could also be neurologically beneficial." (8)

[FIGURE 1 OMITTED]

Assays and Standards for Vitamin D

As mentioned earlier, there are two forms of vitamin D that are important to humans: vitamin [D.sub.3] and vitamin [D.sub.2]. Vitamin [D.sub.3] is obtained from foods of animal origin and from ultraviolet light-stimulated conversion in the skin; small amounts of vitamin [D.sub.2] are obtained from foods of plant origin. Both forms of the vitamin are used to fortify various foods and in over-the-counter supplements. Thus, analytical methods that can accurately quantify both forms are often essential for diagnosis and monitoring patients with vitamin D disorders.

The liquid chromatography, tandem mass spectrometry (LC/MS/MS) method has certain advantages--it does not use radioisotopes and is sensitive and equally specific for both forms of Vitamin D. Concentrations of each form are measured and reported independently. However, it is technically more difficult than other methods, is quite expensive and not available in most clinical laboratories. Concentrations of each form are measured and reported independently.

Two other methods are more common in the clinical laboratory. HPLC also differentiates and quantifies the two forms; currently, this is the most common method. Chemiluminescence is offered on chemistry analyzers but reports the amount of both forms as a single value. Whether this is clinically significant is debated.

In part due to differences in the results of the methods, a universal reference range is difficult to establish. Additionally, there is currently no consensus on the level which indicates deficiency. However, Holick states that "although most laboratories report the normal range to be 20 to 100 ng/mL [50 to 250 nmol/L], the preferred range is 30 to 60 ng/mL [75 to 150 nmol/L]." (9)

There is now a NIST material now available for vendors to use to prepare their calibrators.

Requirements for Vitamin D, Calcium and Magnesium

At this time, there is no agreement on how much of these should be taken. Here is one set of recommendations from the Canadian Government (Health Canada).

Conclusions

As a vitamin that we cannot make within ourselves in physiologically needed amounts, it is important to be aware of the possibilities of a vitamin D deficiency. This is especially important in the northern states (above 40[degrees] latitude) in the northern hemisphere and below 40[degrees] in the southern hemisphere.

A number of diseases besides rickets and bone fractures have been shown to be related to vitamin D deficiencies including Coronary Artery Disease (CAD), some internal cancers and multiple sclerosis.

Assays now exist that allow nearly any laboratory with sufficient test volume to perform the test in house. There are strong arguments for screening some segments of the population including older persons with a history of fractures.

Questions for STEP Participants

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In the following, choose the one best answer for each question.

1 Rickets, like small pox, has been eradicated due to supplementary vitamin D in foods.

A. True

B. False

2 Which of these has NOT been implicated in vitamin D deficiency?

A. Asthma

B. Coronary artery disease

C. Digestive disorders

D. Multiple sclerosis

3 Ultraviolet A is needed for the proper use of vitamin D.

A. True

B. False

4 Vitamin D is a group of polypeptide hormones.

A. True

B. False

5 Vitamin D may increase the risk of coronary artery disease.

A. True

B. False

6 Data do not indicate that vitamin D can reduce the risk of prostate cancer.

A. True

B. False

7 Risk of colorectal cancer is reduced by supplements of vitamin D.

A. True

B. False

8 Data suggest that there is a connection between low levels of vitamin D and multiple sclerosis.

A. True

B. False

9 Which of these has not been used to measure vitamin D?

A. RIA

B. GC/MS

C. Enzyme immunoassay assay

D. HPLC

10 Which of these is the consensus amount of Vitamin D per day?

A. 500

B. 1000

C. 1200

D. None of the above

References

(1.) Craney, A. Effectiveness and Safety of Vitamin D in Relation to Bone Health Evidence Reports/Technology Assessments, No. 158, Agency for Healthcare Research and Quality (US); August 2007. Publication No. 07-E013

(2.) Jones G. Pharmacokinetics of vitamin D toxicity. Am J Clin Nutr. 88:582S-586S, 2008

(3.) Pilz S, et al. Vitamin D supplementation: a promising approach for the prevention and treatment of strokes. Curr Drug Targets. 1;12(1):88-96, 2011. See also Pilz S, Tomaschitz A, Marz W Vitamin D deficiency and stroke: time to act! Am J Cardiol. 106:1674, 2010, and Grandi ,NC., et al. Serum vitamin D and risk of secondary cardiovascular disease events in patients with stable coronary heart disease. Am Heart J. 159:1044-5, 2010.

(4.) Kulie T,et al. Vitamin D: an evidence-based review. J Am BoardFam Med. 22:698-706, 2009

(5.) Potera C., Calcium supplements may increase heart disease risk. Am JNurs.110:18, 2010

(6.) Chung M,et al Vitamin D and calcium: a systematic review of health outcomes. Evid Rep Technol Assess (Full Rep). 183:1420. 2009.

(7.) Zhou G, Stoitzfus J, Swan BA. Optimizing vitamin D status to reduce colorectal cancer risk: an evidentiary review. Clin J OncolNurs. 13:E3-E17, 2009.

(8.) Pierrot-Deseilligny C. Clinical implications of a possible role of vitamin D in multiple sclerosis. J Neurol. 256(9):1468-79, 2009.

(9.) Holick MF. Vitamin D: evolutionary, physiological and health perspectives. Curr Drug Targets.12(1):4-18, 2011. See also Dong Y, et al. A 16-week randomized clinical trial of 2000 international units daily vitamin [D.sub.3] supplementation in black youth: 25-hydroxyvitamin D, adiposity, and arterial stiffness. J Clin EndocrinolMetab. 95:584-91, 2010.

David Plaut, Plano, TX, Consultant, AMT's Book Reviewer, and frequent speaker at AMT regional meetings and national conventions; William McLellan, MS(R), Clinical Chemist, Hollywood, FL
Age     Calcium   Vit. D
           mg/d     U/day

30 - 50    1000      200
51 - 70    1200      400
  71+      1200      600

Magnesium: Females ~ 300; Males 400 mg/d.
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