La Vitamina D, una nueva luz
to maintain good health. The human body cannot make these essential
bio-molecules. They must be supplied in the diet or by bacteria in the
intestine, except for vitamin D. Skin makes vitamin D when exposed to
ultraviolet B (UVB) radiation from the sun. A light-skinned person
will synthesize 20,000 IU(international units) of vitamin D in 20
minutes sunbathing on a Caribbean beach.
Vitamin D is also unique in another way. It is the only vitamin that
is a hormone, a type of steroid hormone known as a secosteroid, with
three carbon rings.
Steroid hormones such as cortisone, estrogen, and testosterone have
four carbon rings. Ultraviolet B radiation in sunlight breaks open one
of the rings in a steroid alcohol present in the skin,
7-dehydrocholesterol, to form vitamin D (cholecalciferol). The liver
changes this molecule into its circulating form, 25-hydroxyvitamin D
(calcidiol, 25[OH]D), the "vitamin D" blood tests measure. Cells
throughout the body absorb 25-hydroxyvitamin D and change it into
1,25-dihydroxyvitamin D (calcitriol), the active form of vitamin D
that attaches directly to receptors on the DNA of genes in the cell's
nucleus.
The vitamin D hormone system controls the expression of more than 200
genes and the proteins they produce. In addition to its well-known
role in calcium metabolism, vitamin D activates genes that control
cell growth and programmed cell death (apoptosis), express mediators
that regulate the immune system, and release neurotransmitters (e.g.,
serotonin) that influence one's mental state.
Severe deficiencies of some vitamins cause vitamin-specific diseases,
such as beriberi (from a lack of vitamin B1, thiamine), pellagra (B3,
niacin), pernicious anemia (B12), and scurvy, (vitamin C). A
deficiency in iodine produces a goiter, mental retardation, and, when
severe, cretinism.
Rickets, a softening and bending of bones in children, first described
in 1651, is another nutritionally-specific disease. It reached
epidemic proportions following the industrial revolution, which began
in the 1750s. In the 19th century, before the importance of exposing
children to sunlight was recognized, the majority of children that
lived in cities with sunless, narrow alleyways and pollution developed
rickets. An autopsy study done in Boston in the late 1800s showed that
more than 80 percent of children had rickets.
Early in the 20th century an investigator found that cod liver oil
could prevent rickets in puppies. The nutritional factor in the oil
that promotes skeletal calcium deposition was named "vitamin D,"
alphabetically after already-named vitamins A, B, and C. Rickets was
thought to be another vitamin-deficiency disease, and the curative
agent, a steroid hormone, was mislabeled a "vitamin."
Now, a century later, a wealth of evidence suggests that rickets, its
most florid manifestation, is the tip of a vitamin D
insufficiency/deficiency iceberg. A lack of Vitamin D can also trigger
infections (influenza and tuberculosis), autoimmune diseases (multiple
sclerosis, Type 1 diabetes, rheumatoid arthritis, and inflammatory
bowel disease), cardiovascular disease, and cancer. Practitioners of
conventional medicine (i.e., most MDs) are just beginning to
appreciate the true impact of vitamin D deficiency. In 1990, medical
journals published less than 20 reviews and editorials on vitamin D.
Last year they published more than 300 reviews and editorials on this
vitamin/hormone. This year, on July 19, 2007, even the New England
Journal of Medicine, the bellwether of pharmaceutically-oriented
conventional medicine in the U.S., published a review on vitamin D
that addresses its role in autoimmune diseases, infections,
cardiovascular disease, and cancer (N Engl J Med 2007;357:266-281).
Up until 1980, doctors thought that vitamin D was only involved in
calcium, phosphorus, and bone metabolism. Then two investigators
proposed that vitamin D and sunlight could reduce the risk of colon
cancer. A growing body of evidence indicates that they were right and
that vitamin D can prevent a whole host of cancers - colon, breast,
lung, pancreatic, ovarian, and prostate cancer among them. Colon
cancer rates are 4 to 6 times higher in North America and Europe,
where solar radiation is less intense, particularly during the winter
months, compared to the incidence of colon cancer near the equator.
People with low blood levels of vitamin D and those who live at higher
latitudes are at increased risk for acquiring various kinds of cancer.
Many epidemiological, cohort, and case control studies prove, at least
on a more likely than not basis, that vitamin D supplements and
adequate exposure to sunlight play an important role in cancer
prevention (Am J Public Health 2006;96:252-261).
There is now strong scientific evidence that vitamin D does indeed
reduce the risk of cancer. Evidence from a well-conducted, randomized,
placebo-controlled, double-blind trial proves beyond a reasonable
doubt that this is the case, at least with regard to breast cancer. A
Creighton University study has shown that women over the age of 55 who
took a 1,100 IU/day vitamin D supplement, with calcium, and were
followed for 4 years had a highly statistically significant (P <0.005)
75% reduction in breast cancer (diagnosed after the first 12 months)
compared with women who took a placebo (Am J Clin Nutr
2007;85:1568-1591).
Some of the genes vitamin D activates make proteins that halt cancer
by inducing apoptosis (programmed cell death), which destroys aberrant
cells before they become cancerous, like adenoma cells in the colon
and rectum. Others promote cell differentiation and reining in of
out-of-control growth of cancer cells (like prostate cancer cells).
Vitamin D-expressed genes inhibit angiogenesis, the formation of new
blood vessels that malignant tumors need to grow, as studies on lung
and breast cancers show. Other genes inhibit metastases, preventing
cancer that arises in one organ from spreading its cells to other
parts of the body, as studied in breast and prostate cancers.
Vitamin D also expresses genes that curb cardiovascular disease. One
gene controls the renin-angiotensin system, which when overactive
causes hypertension (high blood pressure). Others stifle the immune
system-mediated inflammatory response that propagates atherosclerosis
and congestive heart failure (Curr Opin Lipidol 2007;18:41-46).
Multiple sclerosis (MS) is a neurologically devastating disease that
afflicts people with low vitamin D levels. Its victims include the
cellist Jacqueline Du Pré, whose first symptom was loss of sensation
in her fingers, and some 500,000 Americans who currently suffer from
this malady. MS is an autoimmune disease, where the body's immune
system attacks and destroys its own cells. With multiple sclerosis, T
cells in the adaptive immune system, Th1 cells (CD4 T helper type 1
cells), attack the myelin sheath (insulation) of the axons (nerve
fibers) that neurons (brain cells) use to transmit electrical signals.
The Vitamin D hormone system regulates and tones down the potentially
self-destructive actions of Th1 cells. These cells make their own
1,25-dihydroxyvitamin D if there is a sufficient amount of vitamin D
(25-hydroxyvitamin D) circulating in the blood. Researchers have shown
that the risk of MS decreases as the level of vitamin D in the blood
increases (JAMA 2006;296:2832-2838). People living at higher latitudes
have an increased risk of MS and other autoimmune diseases. Studies
show that people who live below latitude 35° (e.g., Atlanta) until the
age of 10 reduce the risk of MS by 50% (Toxicology 2002;181-182:71-78
and Eur J Clin Nutr 2004;58:1095-1109).
In a study published earlier this year, researchers evaluated 79 pairs
of identical twins where only one twin in each pair had MS, despite
having the same genetic susceptibility. They found that the MS-free
twin had spent more time outdoors in the sun - during hot days, sun
tanning, and at the beach. The authors conclude that sunshine is
protective against MS (Neurology 2007;69:381-388).
New research suggests that influenza is also a disease triggered by
vitamin D deficiency. Influenza virus exists in the population
year-round, but influenza epidemics are seasonal and occur only in the
winter (in northern latitudes), when vitamin D blood levels are at
their nadir. Vitamin D-expressed genes instruct macrophages, the
front-line defenders in the innate immune system, to make
antimicrobial peptides, which are like antibiotics (Science
2006;311:1770-1773). These peptides attack and destroy influenza virus
particles, and in human carriers keep it at bay. (Neutrophils and
natural killer cells in the innate immune system and epithelial cells
lining the respiratory tract also synthesize these virucidal
peptides.) Other vitamin D-expressed genes rein in macrophages
fighting an infection to keep them from overreacting and releasing too
many inflammatory agents (cytokines) that can damage infected tissue.
In the 1918 Spanish flu pandemic, which killed 50 million people, of
which 500,000 were Americans, young healthy adults (as happened to my
22-year-old grandmother) would wake up in the morning feeling well,
start drowning in their own inflammation as the day wore on, and be
dead by midnight. Autopsies showed complete destruction of the
epithelial cells lining the respiratory tract due, as researchers now
know, to a macrophage-induced overly severe inflammatory reaction to
the virus. These flu victims were attacked and killed by their own
immune system, something researchers have found vitamin D can prevent
(Epidemiol Infect 2006;134:1129-1140).
Randomized clinical trials need to be done to test the vitamin D
theory of influenza. With what we know now, however, perhaps an annual
shot of 600,000 IU of vitamin D (Med J Aust 2005;183:10-12) would be
more effective in preventing influenza than a jab of flu vaccine.
Our species evolved in equatorial Africa where the sun, shining
directly overhead, supplies its inhabitants with year-round
ultraviolet B photons for making vitamin D. Our African ancestors
absorbed much higher doses of vitamin D living exposed in that
environment compared to the amount most humans obtain today. A single
mutation that occurred around 50,000 years ago is responsible for the
appearance of white skin in humans. It turns out that a difference in
one rung, or base pair, in the 3 billion-rung DNA ladder that
constitutes the human genome determines the color of one's skin
(Science 2005;310:1782-1786). White skin, with less melanin,
synthesizes vitamin D in sunlight six times faster than dark skin.
People possessing this mutation were able to migrate to higher
latitudes, populate Europe, Asia, and North America, and be able to
make enough vitamin D to survive.
The majority of the world's population now lives above latitude 35° N
and is unable to synthesize vitamin D from sunlight for a period of
time in winter owing to the angle of the sun. At a large solar zenith
angle, ozone in the upper atmosphere will completely block UVB
radiation. In Seattle (47° N) and London (52° N), from October to
April UVB photons are blocked by the atmosphere so one's skin cannot
make vitamin D. (The half-life of circulating vitamin D is
approximately one month.) Making matters worse, even when UVB
radiation is available in sunlight, health authorities, led by the
American Academy of Dermatology, warn people to shield themselves from
the sun to avoid getting skin cancer.
Except for oily fish like (wild-only) salmon, mackerel, and sardines
and cod liver oil - and also sun-dried mushrooms - very little vitamin
D is naturally present in our food. Milk, orange juice, butter, and
breakfast cereal are fortified with vitamin D, but with only 100 IU
per serving. One would have to drink 200 8-oz. glasses of milk to
obtain as much vitamin D as skin makes fully exposed to the noonday
sun.
The U.S. Food and Nutrition Board in the Institute of Medicine puts
the Recommended Dietary Allowance (RDA) for vitamin D at 200 IU for
children and adults less than 50 years old, 400 IU for adults age
50-70, and 800 IU for adults over the age of 70. Most multivitamin
preparations contain 400 IU of vitamin D. These guidelines are
directed towards maintaining bone health and are sufficient to prevent
rickets - but not cancer, cardiovascular disease, multiple sclerosis,
or influenza. Without evidence to support it, the board arbitrarily
set the safe upper limit for vitamin D consumption at 2,000 IU/day.
Vitamin D (25-hydroxyvitamin D) blood levels, the barometer for
vitamin D status, are measured in nanograms per milliliter (ng/ml) or
nanomoles per liter (nmol/l), where ng/ml = 0.4 nmol/l. Children and
adults need a vitamin D blood level >8 ng/ml to prevent rickets and
osteomalacia (demineralization and softening of bones) respectively.
It takes a concentration >20 ng/ml to keep parathyroid hormone levels
in a normal range. A level >34 ng/ml is required to ensure peak
intestinal calcium absorption. Finally,
neuromuscular performance steadily improves in elderly people as
vitamin D levels rise up to 50 ng/ml. Accordingly, a vitamin D blood
level <8 ng/ml is regarded as severely deficient; 8-19, deficient; and
20-29, insufficient, i.e., too low for good health. A level >30 ng/ml
is sufficient, but experts now consider 50-99 ng/ml to be the optimal
level of vitamin D. Levels 100-150 ng/ml are excessive and >150 ng/ml,
potentially toxic.
A majority of Americans have insufficient or deficient vitamin D blood
levels. In veterans undergoing heart surgery at the Seattle VA
hospital, I found that 78% had a low vitamin D level: 12% were
insufficient; 56%, deficient; and 10% were severely deficient.
In order to enjoy optimal health, we should maintain a vitamin D blood
level of ≥50-99 ng/ml. Without sun exposure, to reach a level of 50
ng/ml requires taking a 5,000 IU/day vitamin D supplement. There are
two kinds of vitamin D supplements: vitamin D3 (cholecalciferol), the
kind our skin makes, and vitamin D2 (ergocalciferol), a synthetic
variant made by irradiating plants. Vitamin D2 is only 10-30% as
effective in raising 25-hydroxyvitamin D blood levels compared to
vitamin D3, leading the authors of a recent study conclude, "Vitamin
D2 should not be regarded as a nutrient suitable for supplementation
or fortification" (Am J Clin Nutr 2006;84:694-697).
Concerns about vitamin D toxicity are overblown, along with those
about sun exposure. As one researcher in the field puts it, "Worrying
about vitamin D toxicity is like worrying about drowning when you're
dying of thirst." The LD50 of vitamin D in dogs (the dose that will
kill half the animals) is 3,520,000 IU/kilogram. One can take a 10,000
IU vitamin D supplement every day, month after month safely, with no
evidence of adverse effect. (Am J Clin Nutr 1999;69:842-856). A person
must consume 50,000 IU a day for several months before hypercalcemia
(an elevated calcium level in the blood, which is the initial
manifestation of vitamin D toxicity) might occur. Vitamin D in a
physiologic dose (5,000 IU/day) prevents the build up of calcium in
blood vessels. (Circulation 1997;96:1755-1760). If one takes 10,000 IU
of vitamin D a day and spends a lot of time in the sun, it would be
prudent to check vitamin D blood level to ensure that it does not
exceed 100 ng/ml.
Sensible sun exposure should be encouraged, not maligned. If one
avoids sunburn, the sun's health-giving benefits far outweigh its
detrimental effects. A large body of evidence indicates that sunlight
does not cause the most lethal form of skin cancer, malignant
melanoma. A U.S. Navy study found that melanoma occurred more
frequently in sailors who worked indoors all the time. Those who
worked outdoors had the lowest incidence of melanoma. Also, most
melanomas appear on parts of the body that are seldom exposed to
sunlight (Arch Environ Health 1990;45:261-267). Sun exposure is
associated with increased survival from melanoma (J Natl Cancer Inst
2005;97:195-199). Another study showed that people who had longer
lifetime exposure to the sun without burning were less likely to get
melanomas than those with less exposure (J Invest Dermatol
2003;120:1087-1093.)
The rise in skin cancers over the last 25 years parallels the rise in
use of sunscreen lotions, which block vitamin D-producing UVB
radiation but not cancer-causing ultraviolet A radiation (UVA). (Newer
sunscreen lotions also block out UVA.) Each year there are 8,000
deaths from melanoma and 1,500 deaths from nonmelanoma (squamous and
basal cell) skin cancer. Surgical excision of nonmelanoma skin cancers
cures them, except in rare cases where the growth has been allowed to
linger for a long time and metastasize. Dr. John Cannell, Executive
Director of the Vitamin D Council, makes this point: 1,500 deaths
occur each year from non-melanoma skin cancer, but 1,500 deaths occur
each day from other cancers that vitamin D in optimal doses might well
prevent. (The Vitamin D Council website is an excellent source of
information on vitamin D.)
The U.S. government and its citizens currently spend $2,000 billion
dollars ($2 trillion) on "health care," i.e., sickness care, each
year. The cost of taking a 5,000 IU supplement of vitamin D every day
for a year is $22.00. The cost for 300 million Americans taking this
supplement would be $6.6 billion dollars. The number and variety of
diseases that vitamin D at this dose could prevent, starting with a 50
percent reduction in cancer, is mind-boggling. If everyone took 5,000
IU/day of vitamin D, the U.S. "health care" industry would shrink. It
would no longer account for 16 percent of the gross domestic product.
La VITAMINA D, la tenemos disponible en varias presentaciones:
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