Vitamin D and Cancer

An exploration of some of the ways vitamin D may support the prevention and treatment of prostate cancer and other cancers

By Keith I. Block, MD

Some of you may have noticed that this posting was briefly removed from ourblog this morning.  We realized we'd made an error in the way we described the Vitamin D and Taxotere study.  That information has since been corrected.  We apologize for any inconvenience.

Vitamin D is widely known as a bone-building nutrient, mainly because of its ability to enhance the absorption of calcium and bolster overall bone integrity.  But the biological benefits of vitamin D extend far beyond the bone.  Recent research suggests that the so-called “sunshine vitamin” may play a role in helping combat cancer, depression, diabetes, heart disease, hypertension, multiple sclerosis, muscle weakness, and osteoarthritis.  For most of these D-disease links, however, the data are still rather weak and additional research is needed.

The cancer connection arose initially from the observation that populations in northern latitudes experienced more bone thinning with age and also had higher rates of various cancers.  People in colder climates spend more time indoors and therefore get less sunshine – the essential stimulus for vitamin D production in the skin (most cases of vitamin D deficiency are, in essence, a sunshine deficiency).  Eventually, laboratory studies found that high-dose vitamin D helped block the growth of cancers of the breast, colon, rectum, prostate, lung and head/neck region, as well as lymphoma, leukemia and multiple myeloma.

Now, it’s tempting to believe that simply taking vitamin D in high doses could offer a way to treat these cancers.  Alas, few things in cancer care are that clear-cut.  One reason high-dose vitamin D is not a simple solution is that the vitamin D you get from sunshine or from your diet does not act directly:  Your body must first convert the basic form of the vitamin (cholecalciferol) into its active form (calcitriol), and this ability can be hampered in certain disease and treatment situations—as when kidney functioning becomes compromised.

Oncologists are now studying vitamin D – mainly in the form of calcitriol – as part of standard therapy for various cancers.  In the case of prostate cancer, for example, vitamin D appears to slow the growth of prostate tumors.  In 2005, Dr. Reinhold Vieth and his colleagues at the Toronto-Sunnybrook Regional Cancer Centre in Toronto, Canada, investigated the impact of a vitamin D supplement on the levels of prostate-specific antigen (PSA), a marker for the progression of prostate cancer.

The study focused on fifteen men who had relapsed following surgery or radiation treatment for prostate cancer.  Typically, when these “local treatment” strategies fall short, the PSA level begins to rise steadily.  In the absence of overt symptoms of cancer, there is no consensus among oncologists as to what the best course of treatment should be.  However, the research on vitamin D suggests great promise and an intervention that should be considered.

In the Toronto study, all of the prostate cancer patients took 2,000 IU of vitamin D in its natural form (cholecalciferol).  This dose is five times greater than the current RDA, but it’s also the dose that many scientists now believe is optimal for adults.  Dr. Vieth chose cholecalciferol, the basic form of vitamin D, even though calcitriol already had been shown to delay the increase in PSA levels in this context.  The problem with calcitriol, however, is that near-toxic doses are required to reach therapeutic levels.  Calcitriol must be taken daily to have an effect, whereas vitamin D has more drawn-out effects and need not be taken daily.  Also whereas vitamin D is very cheap, calcitriol is quite expensive – and generally not covered by insurance.

Here’s what the Toronto researchers reported in the June 2005 issue of Nutrition and Cancer.  In nine of the fifteen patients, PSA levels either dropped or stayed the same after starting the vitamin D.  This was sustained for as long as 21 months.  The PSA doubling time, an indicator of the rate of tumor growth, went from 14 months before vitamin D to 25 months after starting the vitamin D supplement.  What’s more, all but one of the patients showed an increase in the PSA doubling time after going on the high-dose vitamin D, and no side effects were reported.

This is just one of a number of exciting examples of the potential for vitamin D to improve cancer treatment outcomes.  Other studies suggest that the vitamin may also curb the deadly processes of tumor invasion, angiogenesis, and metastasis – all of which tend to make prostate cancer and other solid tumor malignancies more aggressive and less amenable to treatment.

Most of the treatment-related focus has been on calcitriol (remember, your body must convert the basic form – cholecalciferol – into the active form, calcitriol) rather than vitamin D per se.  Perhaps the most exciting example is calcitriol’s impact on the use of Taxotere (generic name: docetaxel) in the treatment of prostate cancer.  Adding high-dose calcitriol one day prior to taxotere led to a statistically significant improvement in survival compared to patients receiving taxotere plus a placebo.  Patients in the calcitriol group saw their risk of death lowered by about a third, according to the principal investigator, oncologist Tomasz Beer of Oregon Health Sciences University.  Dr. Beer and his colleagues are now studying this regimen in a second clinical trial involving androgen-independent prostate cancer.

We now know that calcitriol acts in a synergistic way with dexamethasone and several kinds of chemotherapy drugs, including doxorubicin, paclitaxel (Taxol), platinum compounds (e.g., cisplatin), and mitoxantrone.  But the benefits may go even further than that.  We know that dexamethasone enhances the tumor-inhibiting effects of calcitriol.  The combination of tamoxifen and calcitriol results in enhanced killing of breast cancer cells.  Soy isoflavones, too, seem to synergize with calcitriol as well as with normal vitamin D.

Finally, in cases of advanced metastatic prostate cancer, there is evidence that vitamin D or calcitriol can be very effective in slowing down the breakdown of bone and lessening bone pain.  This is important, because many men with prostate cancer have damaged kidneys and therefore probably require calcitriol rather than the precursor form of the vitamin.  Our own clinical data with advanced prostate cancer strongly support this: even with highly metastatic disease, we have seen good results when combining high vitamin D supplementation and other synergists with standard therapy.  Knowing how to combine the proper doses of vitamin D with synergists such as soy genistein, could turn out to play a vital role in the treatment and management of these diseases.

Comments

[Natalie]

I feel like we are at the tip of the iceberg with research on vitamin D and cancer. I can't wait to see what future studies reveal, especially for other hormonally involved cancers such as breast ca. Could you shed some light on what optimal serum levels of vit D should be?

[rhinoplasty cost]

Most people get the vitamin D they need through sun exposure. Can also be obtained through the diet, but very few foods naturally contain vitamin D. Vitamin D fortification is permitted in milk and dairy products, cereal flours and related products, margarine, food products, soy and fruit juices and fruit juices.

[stage iv lung cancer]

It would be a big help for everyone for all cancer sufferers if this will be given more attention. Yeah, further studies needs to be done first for this to be recognized and to be used as treatment for the killer disease, cancer.

[clinical oncology]

In most of the cases of bone cancer, it is secondary cancer of bone that means the cancer from other parts of the body is spread to the bone. When cancer is caused in various parts of the body such as lungs, breast, kidneys or prostrate glands and it is in the advanced stage then it get metastasized to the bone causing specific symptoms.