[NOTE: See the remarks about vitamin D's Anti-angiogenic properties below.
This may have relevance to the flap over
angiostatin & endostatin.]
When a Western-style diet that is high in fat but low in calcium and
vitamin D is fed to mice, by the eighth week the animals begin to develop
precancerous growths in their colons. But if the same mice are then given
two sources of calcium these changes are routinely reversed (Richter,
et al., Carcinogenesis 1995;16:2685-2689).
Until now, vitamin D has been considered primarily important as a regulator
of normal bodily levels (or 'homeostasis') of calcium. But, in addition
to its role as a facilitator of calcium absorption, vitamin D now appears
to have other profound effects in the body. Moderate amounts of the vitamin
may help slow the growth not just colon but breast and prostate cancer,
independent of its effect on calcium absorption.
"It's becoming increasingly clear that vitamin D has a host of effects
in the body, especially on the growth of tumor cells," David Feldman,
MD of Stanford University told a seminar sponsored by the American Institute
for Cancer Research in Washington, DC last year.
PROSTATE
For example, intensive work is being done on the link between low vitamin
D levels and prostate cancer. In fact, there is a possibility of even
using the vitamin to treat the disease. The aforementioned 1,25-D form
of the vitamin has induced several important responses in prostate cells,
including growth inhibition.
Dr. Feldman and colleagues recently concluded that "vitamin D is
anti-proliferative and promotes cellular maturation." It seems clear,
they add, "that vitamin D must be viewed as an important cellular
modulator of growth and differentiation....Vitamin D has the potential
to have beneficial actions on various malignancies including prostate
cancer."
1,25-D may prove useful in chemoprevention, they say, and/or in differentiation
therapy. They maintain an "optimistic view on the possible use of
vitamin D to treat prostate cancer in patients," and say that "further
investigation is clearly warranted" (Adv Exp Med Biol 1995;375:53-63).
Recently, new forms (analogs) of vitamin D have been developed that have
much less effect on calcium metabolism, but still retain the vitamins
tumor inhibiting properties. The action of the vitamin seems to be regulated
by a single receptor site, which has the same structure as certain steroid
receptors (Niles, RM. Adv Exp Med Biol 1995;375:1-15).
Canadian scientists have reported that in the test tube cancer cell proliferation
is "strongly inhibited" by both vitamin D and its analogs. In
some systems, they say, the analogs (such as EB1089) were 10 to 100 times
more potent than the original compound. This activity "predicts their
potential usefulness" in animals in inhibiting squamous cancer growth
(Yu. J, et al. Anticancer Drugs 1995;6:101-108)
Prostate cancer is especially prevalent and deadly among African-American
men. What could prevent early prostate cancer from progressing to the
malignant phase? It has been found that higher serum levels of vitamin
D might do this in both Black and white men. This is so especially after
the age of 57.
Scientists have concluded that vitamin D metabolism may indeed impact
the risk of prostate cancer (Corder, EH, et al., Cancer Epidemiol Biomarkers
Prev 1995;4:655-659).
When human prostate cancer cells were implanted into so-called "nude"
mice (which are bred to lack a normal immune systems),Vitamin D slowed
malignant growth. Several other studies lend credence the idea that vitamin
D cancer protect against prostate cancer.
For example, in one study, serum levels of "1,25-D" (the major
circulating form of the vitamin) were significantly lower in 181 men who
had been diagnosed with prostate cancer, compared to their age-matched
controls. The author of that study, Elizabeth Corder, MD, has said that
levels of the vitamin could be used as an important way of predicting
the risks for prostate tumors.
A study from the University of North Carolina found that men living in
northern latitudes are at greater risk of developing prostate cancer.
Such men have less exposure to ultraviolet radiation, the principal source
of vitamin D in the body. This observations further supports the theory
that having lowered levels of vitamin D predisposes men to prostate cancer.
BREAST CANCER
At a meeting of the US President's Cancer Panel Special Commission on
Breast Cancer, convened in Reston, Va. on 9/23/92, British scientists
David Hunter and Dimitrios Trichopoulos reported on a strong inverse correlation
between breast cancer mortality in the US and exposure to ultraviolet
sunlight.
Since vitamin D is created by exposure to sunlight, this suggested that
low levels of vitamin D plays a part in the onset of cancer (Lancet1992;340:905).
In addition, scientists writing in the Cancer Letter analyzed the anticancer
effects of vitamin D and four of its analogs on a human breast cancer
cell line. Growth of such cells was "significantly inhibited"
by all such compounds. These results demonstrate that analogs of vitamin
D are "potent antiproliferative agents on human breast cancer cells"
(Brenner, RV, et al., Cancer Lett, 1995;92:77-82).
The same researchers also showed that levels of the vitamin were lower
in patients with colon cancer than in controls. The mechanism of action
is unclear. However, it is known that both calcium and vitamin D can be
deterrents to colon cancer. Since the vitamin is necessary for the absorption
of the mineral, it seems to be their dual action that halts the proliferation
of colon epithelial cells.
MELANOMA LINK
These latest findings support the theory of Drs. Frank C. and Cedra F.
Garland. Between 1974 and 1984, they studied 176 cases of melanoma among
Navy personnel. After testicular cancer, melanoma is the second most-common
cause of cancer in male US Navy personnel (Archives of Environmental Health
1990;45:261-267).
Melanoma is usually associated with excessive exposure to the sun. However,
it was found that sailors who had indoor jobs (e.g., on engine crews)
actually had an incidence of melanoma that was higher than those who worked
outdoors. Those who spent some time outdoors (but not an excess of time)
seemed to actually benefit by generating vitamin D from the sun.
The Garlands concluded there may be a protective effect from brief but
regular exposure to sunlight. Vitamin D may suppress malignant melanoma.
ANTI-ANGIOGENESIS
Vitamin D and its derivative compounds also have been shown to inhibit
tumor growth in mice with a deadly form of eye cancer called retinoblastoma.
In humans, this is a rare cancer, afflicting about 200 individuals per
year, most of them children. Until now, the mechanism of vitamin Ds action
in this experimental tumor has not been understood. But in 1995, Boston
scientists gave these mice either high or low doses of vitamin D in mineral
oil by injection, five times per week for five weeks.
The control animals were injected with mineral oil alone. At five months
of age, the animals were killed and their eyes processed for analysis
by light microscopy.
Mice receiving high-dose vitamin D had formed the lowest numbers of blood
vessels in the eye. This was followed by the low-dose vitamin D group.
But the control group showed the highest blood vessel countãalmost
double that of the first group. The number of blood vessels in this particular
animal model is indicative of retinoblastoma.
The scientists concluded that vitamin D could definitely exert anticancer
effects through the inhibition of new vessel formation, or angiogenesis
(Shokravi, MT, et al., Invest Ophthalmol Vis Sci, 1995;36:83-87). This
type of tumor inhibition is "hot" right now. It is not only
the basis of the work of some well established scientists (see p. 6) but
is a purported mechanism of action for shark cartilage.
TO SUPPLEMENT OR NOT?
While some scientists in Holland recently concluded that there are "insufficient
reasons to supplement subjects at increased colon cancer risk with calcium
or vitamin D,<especially if they are getting the recommended amounts
in their diets (Kleibeuker et al., Eur J Cancer 1995;31A:1081-1084), many
others would strongly disagree.
How do we know if a person is truly getting enough vitamin D? Because
they drink a lot of milk? It is quite disturbing that the vitamin D content
in milk--the major source of the vitamin in the Western diet--may be serious
misrepresented.
A report by Tai C. Chen, PhD, of Boston University School of Medicine,
and other researchers, found that 80 percent of the milk samples in the
U.S. contained either 20 percent less or 20 percent more vitamin D than
the label claimed. In fact, fourteen percent of the samples had undetectable
amounts of the vitamin (New Engl J Med 1993;329:1507).
Supplements of vitamin D are usually found together with vitamin A. These
typically contain 400 IUs of vitamin D. The cost of each such tablet or
capsule is between three and five cents. This is a harmless amount to
take. It seems to be a very small price indeed to pay for some possibly
significant protection against melanoma, prostate, colon, and breast cancer.
