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
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
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
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
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
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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the $6 processing fee per article.
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.
2 Which of these has NOT been implicated in vitamin D deficiency?
B. Coronary artery disease
C. Digestive disorders
D. Multiple sclerosis
3 Ultraviolet A is needed for the proper use of vitamin D.
4 Vitamin D is a group of polypeptide hormones.
5 Vitamin D may increase the risk of coronary artery disease.
6 Data do not indicate that vitamin D can reduce the risk of
7 Risk of colorectal cancer is reduced by supplements of vitamin D.
8 Data suggest that there is a connection between low levels of
vitamin D and multiple sclerosis.
9 Which of these has not been used to measure vitamin D?
C. Enzyme immunoassay assay
10 Which of these is the consensus amount of Vitamin D per day?
D. None of the above
(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.
(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.
(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
30 - 50 1000 200
51 - 70 1200 400
71+ 1200 600
Magnesium: Females ~ 300; Males 400 mg/d.