The connection between vitamin D and reduced cancer risk is certainly one of
the most controversial chapters in his book.

There is certainly ample reason to suspect that vitamin D reduces the risk of
cancer. But perhaps to best understand the rationale of that statement I should
start by reviewing how cancer develops.

During embryogenesis the embryonic cells differentiate into the distinctive cells
of each tissue in the body. Then they adhere together to form the organs of our
body and stop dividing.

We can think of cancer as the reverse process. A cancer cell de-differentiates,
starts dividing in an uncontrolled manner and loses the ability to adhere to
the other cells of the organ from which it originated.

And vitamin D is one of the master hormones that prevents that from occurring.
It binds to receptors on the cell surface and activates cellular pathways that
put the brakes on cell division, maintains the cell in the differentiated state
and causes them to adhere to other cells.

And this is apparently true of cancer cells as well as normal cells. Dr. Holick
and his colleagues have shown that when vitamin D is added to the culture medium of
prostate cancer cells they stop growing and return to prostate cells.

But that is a cell culture experiment. What is the evidence that vitamin D reduces cancer
risk in people?

There is a lot of evidence, but most of it is indirect.

For example, there are studies that show:

- Men with high sun exposure are 3 times less likely to
develop prostate cancer than men with minimal sun
exposure.

- Women who are deficient in vitamin D at the time they
are diagnosed with breast cancer are 75% more likely to
die from the disease than women who had adequate levels
of vitamin D in their bloodstream at the time of
diagnosis.

- A 2 year intervention study showed that supplementing
with 2,000 IU of vitamin D/day in men with prostate
cancer reduced the rate at which their PSA levels
increased by 50%.

- a 2007 study showed that postmenopausal women who
supplemented with 1,400-1,500 mg of calcium and 1,000
IU/day of vitamin D for four years reduced the risk of
developing cancer of all causes by 60% compared to the
placebo group.

Based on these and many other studies, Dr. Holick
estimates that if people in this country just took an
extra 1,000 IU/day of vitamin D it would reduce the
risk of developing colorectal, breast, prostate and
ovarian cancer by 50%.

What is the bottom line for you?

Not all experts are convinced that vitamin D will reduce the risk of cancer. And I
would agree that we don’t yet have enough double blind. placebo controlled
intervention studies to definitively prove that a little extra vitamin D will prevent
cancer or slow its progression.

However, as I have said previously an extra 1,000 to 2,000 IU of vitamin D is cheap,
safe and will help strengthen our bones. Cancer prevention, if it does occur, would
just be a side benefit.

*Dr. Michael Holick’s book, “The Vitamin D Solution