D Defends Against Colon Cancer
(HealthScoutNews) -- If you eat a high-fat diet and want to avoid
colon cancer, consider washing your food down with low-fat milk
instead of soda.
The vitamin D in milk and other foods can help protect against the
disease by neutralizing a cancer-causing acid the liver produces
to help digest fatty foods, a new study says. A high-fat diet is
a known risk factor for colon cancer.
The research has established the exact mechanism by which vitamin
D acts to prevent colon cancer. A report in tomorrow's issue of
Science by two scientists sponsored by the Howard Hughes
Medical Institute shows just how vitamin D does the job. It also
sets a course toward finding drugs that can do an even better
The background to the work is "a long history of epidemiological
and experimental data, sometimes confusing and controversial,
about the role of the Western high-fat diet in colon cancer and
the protective effects of vitamin D," says David J. Mangelsdorf,
a Howard Hughes researcher who is professor of pharmacology at
the University of Texas Southwestern Medical Center.
Working first in cell cultures and then in mice, Mangelsdorf
and Ronald M. Evans, a Hughes researcher at the Salk Institute,
have outlined just what happens when you eat a hamburger-and-fries
"You increase the metabolism of bile acids, one of which
is lithocholic acid (LCA)," Mangelsdorf says. "LCA is
extremely toxic, one of the more toxic substances in the body.
Most bile acids are made in the liver, go into the intestine where
they help absorb fatty foods, and then go back to the liver, where
they are stored. LCA cannot go back to the liver. It stays in
the colon, where it can damage DNA and induce colon cancer."
It's been known that vitamin D can prevent that genetic damage.
The Hughes researchers find this protective effect is due to the
fact that LCA binds to the same receptor on cell surfaces as does
vitamin D. When vitamin D binds to the receptor, it sets off a
chain of events by which LCA is rendered harmless. However, if
there is not enough vitamin D or too much LCA, "you overwhelm
the system, and so you get colon cancer," Mangelsdorf says.
"This suggests a new therapeutic mechanism that we have
not yet tapped," he says. "We can develop potent drugs
that activate the vitamin D receptor."
Such drugs would be welcome because they could avoid the side
effects of excess vitamin D, which include nausea, weight loss
and weakness. Too much vitamin D also raises blood levels of calcium
excessively, which can cause other adverse effects.
"That is one of the goals of our research," Mangelsdorf
says. "Our next step is to identify compounds that do not
have the side effects of vitamin D but do have its protective
Evans, a professor of gene expression at the Salk Institute,
is involved in the same effort. In addition to the vitamin D receptor,
he says, there are two other receptors for LCA and other bile
acids. "Each of these provides an opportunity for potential
pharmaceutical and therapeutic intervention," he says.
Until such compounds come along, an obvious protective measure
is to get an adequate amount of vitamin D in the diet. Milk has
long been fortified with vitamin D to prevent rickets; one cup
of milk provides a quarter of the daily recommended dietary allowance.
Sunlight makes the body produce vitamin D; rickets was prevalent
in yesterday's crowded, sunless slums. Other dietary sources of
vitamin D are egg yolks, cod liver oil, prepared cereals (which
are fortified with it), margarine (also fortified), and fish such
as salmon, mackerel and sardines.
Guidelines say an adequate intake is 200 international units
(IU) a day for ages 19 to 50, 400 IU daily for ages 51 to 69 and
600 IU daily for 70 and over.
There's an equally effective dietary strategy that carries other
benefits, Mangelsdorf says: eat less fat.
"Our bodies never evolved the ability to sustain a high-fat
diet that is a property of modern society," he says. "Our
bodies were never intended to see that much fat. The pathological
consequences of a high-fat diet include not only colon cancer,
but also diabetes and cardiovascular disease. The best drug is
to modify your diet."
Vitamin D also helps prevent osteoporosis, and studies have
shown it can cut the risk of diabetes in children.
What To Do: You can learn all about the benefits and
risks of vitamin D and how to get enough of it from the National
Institutes of Health. Learn more about colon cancer from the
Reference Source 101