A report in the current issue of the American Journal of Clinical Nutrition is certain to raise once again the role of vitamin D in preventing cancer.
The researchers, from the
However, when they decided to look at the same study group to determine whether calcium with or without additional vitamin D supplementation had an impact on the incidence of cancer, they found a stunning 78% decrease in the risk of developing cancer in those women who took both calcium and 1000 units of vitamin D3 daily for four years.
This is essentially the first study that has provided any evidence from a forward looking, randomized controlled trial which randomly assigned study participants into various treatment groups.
One third of the 1179 post-menopausal women—who lived in Nebraska—received a placebo (or dummy pill), one third received 1400-1500 mg of calcium supplements daily, and one third received the calcium with the addition of 1000 IU of vitamin D3 (on further chemical analysis, the researchers found that the actual amount of vitamin D3 in the pills was 1100 IU).
The women were all post-menopausal, with an average age of 66.7 at the time they entered the study. As a group, they were overweight, bordering on obesity with an average BMI of 29 (a BMI of 25 to 29.9 is considered overweight; greater than 30 is obese).
The researchers determined how many women in each group developed non-skin cancer AFTER having participated in the study for one year. The researchers made that arbitrary cutoff in order to eliminate cancers that, in their opinion, may have already been present at the time the study began.
As I mentioned, the results were stunning: the risk of developing cancer over the four year time-frame in the women who took both the calcium and vitamin D was 78% compared to the placebo group.
For women who took only calcium, there was a decrease of about 41% in the risk of developing cancer.
The numbers of cancers diagnosed from year 2 to 4 of the study were actually small (as would be expected in a study of this size): there were 18 cancers diagnosed in the placebo-treated arm of the study; 15 cancers in the calcium arm, and 8 cancers in the calcium/vitamin D treatment group.
The numbers of cancers for any particular tumor type were also small, and included cancers of the breast, colon, lung, lymphoma/leukemia, uterine cancer and “other” cancers.
Because of these small numbers, it was not possible to determine whether any particular cancer type was especially affected by treatment with vitamin D.
What was apparent from the study was that taking vitamin D tablets did increase the blood levels of vitamin D, and that there was a direct correlation between these levels and the reduction of cancer incidence.
So where does this study fit into the bigger picture of vitamin D in relation to cancer prevention?
First, it is certainly a very intriguing and provocative report.
There have been many studies reported over the past couple of years suggesting that vitamin D can reduce cancer risk, and that more vitamin D in the body is correlated with a lower risk of several cancers. In fact, in a previous blog, I mentioned that although I had initially been a skeptic of that relationship, I had been converted into a “believer” that in fact there may be such a relationship.
This study adds to that body of evidence.
Unfortunately, this study is simply too small to make an absolute conclusion that the relationship does in fact exist. It is not sufficient in my opinion to make a major recommendation that everyone should start taking 1000 IU of vitamin D3 every day.
Why am I not convinced?
Bottom line, as I have written and commented previously, we need more research in this country to understand the basics of vitamin D in our
We need to understand the impact of geography, ethnicity, personal habits and many other factors on vitamin D levels.
We need to determine whether we should in fact be measuring vitamin D levels routinely as part of preventive medical care.
We need our major national research organizations who monitor this literature to get on with the process of reviewing the data and making evidence based recommendations on what the correct amount of vitamin D supplementation—whether in our diets or through pills—should be for our daily intake.
Perhaps most important is, in my opinion, the need for a well-designed, prospective trial to determine whether or not vitamin D actually reduces cancer risk.
There are too many other instances where the data has appeared compelling that a particular vitamin or drug that might prevent cancer. This evidence is frequently based on what I will call indirect evidence. Once the appropriate prospective trial was conducted, we too frequently find that the results were negative or worse.
The research into beta-carotene comes to mind. A “harmless” vitamin, beta-carotene was thought to reduce the risk of lung cancer. When it was put into a randomized, controlled prospective trial, however, it was found to actually INCREASE the rate of lung cancer.
In regards to the present vitamin D study, 4 years to me seems an awfully short time to demonstrate a true preventive effect of vitamin D.
We know that many cancers take years to develop. In fact, in my personal opinion, many of the cancers that this study concludes were “prevented” in fact were present at the time the study was started.
I suspect there is something else going on here, and it is not prevention. It is more likely a direct effect on the pre-existing cancer, a slowing of growth, or some other phenomenon, but not prevention. It is also possible that the effect may be due to some other, unrecognized factor (I want to be clear that this is not a criticism of the researchers, who are considered to be excellent clinical scientists by their colleagues).
Four years is simply too short a time to have this dramatic effect if prevention was the primary effect of vitamin D supplementation.
Finally, what we definitely do NOT recommend is that people start seeking the sun or use tanning beds as a source of vitamin D with the intent to decrease their risk of cancer.
Small amounts of sun exposure for this purpose are OK for most people, but each person has their own vitamin D and skin “personalities” that dictate their risk of skin cancer, and dictate how much sun exposure they need to get an adequate amount of vitamin D. Where you live also has an impact on skin cancer risk, as well as the amount of vitamin D you might produce from a particular amount of exposure to the sun.
Ultraviolet rays have their own harms and are not a good way to get vitamin D. That doesn’t mean you should be a hermit, but when you go outside—particularly when the UV index is 3 or greater—you should engage in sun-safe behaviors, such as wearing a shirt, wearing a hat, using plenty of sunscreen, and wear UV-protective sunglasses.
In the interests of full disclosure, my Canadian colleagues (and friends) at the Canadian Cancer Society have come out with an advisory today that suggests all Canadians take a daily supplement of 1000 IU of vitamin D.
The Canadians decided to move forward because of the fact that sun exposure in
My colleagues here at the American Cancer Society have decided not to make such a recommendation, pending additional research discussed above.
We need our governmental agencies that review the evidence and determine the recommendations for dietary guidelines to start taking a careful look at their current vitamin D recommendations, so we can have clear guidance–based on currently available evidence on the role of vitamin D in cancer and other diseases—as to whether or not we should make a nationwide effort to increase vitamin D intake.
In the meantime, what should you do?
I can’t make a recommendation outside of the current guidelines, which are age and dose dependent. It is up to you and your health clinician to determine whether or not you should be taking more vitamin D, based on your own personal risk profile.
You should be aware that the current study used 1000 IU a day of vitamin D3. Other studies have shown lower doses of 400 IU daily did not decrease the risk of colon cancer in post-menopausal women (there were some issues with the design of that study), while another study looked at pancreatic cancer risk in men and found that 400 IU a day significantly reduced their risk of that disease.
In my opinion, it is time to make the investment in getting the definitive answers to these questions.
As I mentioned, the results of the study discussed here were impressive, but they are limited in their practical impact in my opinion.
We need to expand our understanding of the role of vitamin D in our health, and get solid answers to our questions so that we can find out once and for all whether or not this vitamin is truly the miracle that some claim it to be.