Does Vitamin D Really Reduce The Risk Of Cancer?

The vitamin D issue has arisen once again.


Back in April, at a major national scientific conference, a Harvard researcher gave a talk on the role of vitamin D in the prevention of cancer.  The lecture, which is available online, was well done and based on scientific data.  (See presentation by Dr. Edward Giovanucci on this webpage.) It didn’t get much notice, however, until an Associated Press reporter did a story on it a couple of weeks later.


That’s when the proverbial “stuff” hit the fan.  Media outlets around the world jumped on the story immediately and fanned the flames that vitamin D was the answer to decreasing the incidence of several forms of cancer that afflict hundreds of thousands of people every year in the United States.


Other scientists were a bit more reserved in their thinking, but still were of the opinion that this is an area that needs further examination and consideration.


One of the major concerns of many, including me, was that the public would read only one half of the story, namely that sun exposure (the major source for the production of Vitamin D in the body) was good for you, and that it was now considered a good thing to go out in the sun, get a tan, but just not get a sunburn.


For example, I was interviewed on the Fox News Channel, and while I was talking in a studio in Washington, the channel apparently was showing pictures of people sunbathing on the beach.  That was a hard visual to overcome with scientific words that most people probably weren’t paying much attention to.


The reason so many folks in the medical community were concerned was that we have spent a good deal of time (and money) trying to educate people about the dangers of sun exposure.  We have an increasing frequency of skin cancers, including melanomas which are the most dangerous form of skin cancer.  There are also other skin related problems, such as premature or extensive aging of the skin, that result from sun exposure.


And we can’t forget the young people, especially young women, who mistakenly believe that a good tan is a sign of good health.  The vitamin D story had the risk of giving them the ammunition they needed to overcome whatever reservations their parents may have had about sun exposure and tanning booths.


Since this story “broke” in the early summer, there was the real possibility that a lot of good work could be undone by people who didn’t understand the entire issue.  And that in no small part is because scientific organizations, including the American Cancer Society, did not feel the science was in place (including detailed, careful discussion of the data) to change our current recommendations and provide guidance that going out in the sun was in fact a good thing for you (see our web page for further information).


How did we get into this predicament in the first place?


It has been clear to many researchers for some time that there is a distribution in the incidence of cancers in this country based on where people live.  There are maps which very nicely demonstrate that where you live may influence your risk of developing certain cancers.


That observation led some to conclude that sun exposure may be a factor in cancer incidence given that more sun at certain latitudes was associated with a lower incidence of these cancers.


This has led some researchers to conclude, based on certain studies, that the reason this effect occurs was due to an increase in vitamin D levels, which occurs with greater exposure to the sun.  That in turn led to the report in April, and the following media frenzy.


What did not get answered by the maps was whether other factors could also play a role, whether that be dietary habits or physical exercise or some other unknown factor.


Research has shown us time and again is that it frequently is not so obvious why we see certain patterns of disease.  It takes a lot of research effort and careful examination of the data to understand biological phenomenon, such as the development of cancer.


In the interval since the events of this past summer, many organizations (including the American Cancer Society) have begun to look more closely at the question, and try to get some consensus on what recommendations we can make to the public. 


Critical to this effort is confirming the science, and making recommendations that take into account the benefits and risks of sun exposure, as well as how to guide people who live in different parts of the country which may have more or fewer sunny days, for example.  And we can’t forget that many of us have different types of skin pigmentation.  Some are very sensitive to the sun, some less so.  Some of us are African American, and sun exposure would not be sufficient to get adequate levels of vitamin D which means we would have to take dietary supplements (more about that later in this discussion) if we are to get the benefit of adequate levels of vitamin D, if the theory proves to be correct.


While I was on vacation these past couple of weeks, two new papers were published in scientific journals once again discussing vitamin D research and promoting the vitamin as a means to reduce cancer incidence.  Both the papers shared many of the same authors.


In The Journal of Steroid Biochemistry and Molecular Biology, the researchers looked at the question of whether there is a “dose-response” relationship between either vitamin D levels in the body or the intake of vitamin D on the incidence of colorectal cancer.  They concluded from their research that either an intake of oral vitamin D of 1000 IU/day or a high level of vitamin D in the blood reduced the incidence of colorectal cancer by 50%.


One of the interesting observations in this paper was the fact that 95% of our vitamin D actually comes from sun exposure.   As a result, many of us are vitamin D deficient, since we spend much of our time indoors.  Also, if you live in Boston, the authors note that there are 2007 hours/year of sunlight, compared to 1400 hours/year in Boston.  Finally, a dose of 1000IU of vitamin D, according to the authors, is safe.  They comment that the National Academy of Sciences has established a “maximum safe level” of vitamin D intake of 2400 IU/day, far more than many of us get and well above the1000 IU level recommended in the research paper.


The other paper, which appeared in the American Journal of Public Health, was more descriptive of the research that has been done on vitamin D in general in relation to cancer.  In this article, the authors mentioned that there is a high prevalence of vitamin D deficiency in the United States.  They also pointed out that some research studies (although not all) have suggested that higher levels of vitamin D can reduce the risk of developing colon, breast, prostate and ovarian cancer.


Prostate cancer studies are an interesting example of how this subject can be confusing.  The authors report of 24 studies of prostate cancer and vitamin D, 13 showed a positive benefit, one suggested a benefit, and 11 showed no association.  In the scientific world, this is not what we would call a “home run.”  Similar inconsistent results were found with other cancers as well.


The authors conclude their report by recommending that we increase our oral vitamin D intake to 800-1000 IU/day.  They also recommend a daily sun exposure of 15 minutes daily in the summer and 20 minutes in the early fall or late spring, “from 11AM to 2PM under clear skies, assuming exposure of arms, shoulders and back.  Blacks require twice as long.  During November to March, north of 37 degrees latitude in the Northeastern and mid-Atlantic regions, no amount of solar exposure is sufficient.”


They also caution that moderation is appropriate, and acknowledge the damage the sun can cause.  They emphasize the need to avoid a sunburn, and that intentional exposure of the face should be minimized.  They go on to say that “oral vitamin D3 supplementation, rather than solar exposure, should be used by fair-skinned or sun-sensitive persons or by individuals taking medicines causing photosensitivity.”


I am not providing all of this information because I agree with the authors, their recommendations, or their conclusions.  Past experience has shown there is much more to be known about whether or not vitamin D really reduces the risk of cancer.  Further research must be done, because there are also risks associated with the type of sun exposures noted above.  Not to mention that it is very, very difficult to make a “one size fits all” recommendation regarding the amount and timing of sun exposure that will achieve the desired effect.


In particular, I do not agree with the statement that we will have 50% fewer colon cancer deaths if everyone starts taking increased amounts of vitamin D and if doctors start routinely measuring vitamin D levels as part of the annual physical, as the authors recommend.


As with any cancer, colon cancer has a complex etiology.  We do know that if we screened more people at average risk age 50 and older we would reduce the incidence and deaths from colon cancer.  I’m not certain, on a personal level, that in the real world increasing vitamin D levels would have the same effect.


That’s not to say that this theory is necessarily incorrect.  That is not my message.  But it is one that requires scrutiny and analysis.


As I mentioned earlier, many of us wish that the real world was only so simple.  Yes, we have seen remarkable advances in health as a result of understanding vitamins (vitamin C and folate come to mind, among others) where bad diseases have had a remarkable reduction in incidence as a result of vitamin supplementation.  Although vitamin D may have a role in cancer prevention, we need to do the research that will demonstrate that conclusively.  Past experience shows us that vitamins which were thought to be beneficial relative to reducing cancer risk actually were harmful.


So there are no easy answers.  I have provided this overview so you can make your own decision.  But bear in mind the jury is still out on this one, no matter how many times the newspapers, radio and TV repeat the message.

4 thoughts on “Does Vitamin D Really Reduce The Risk Of Cancer?

  1. Vitamin D is a great help to prevent cancer. I take sun every day for about 20 to 30 minutes. Problems occur when people have a very bad diet and their body is releasing toxins through the skin. These toxins when exposed to the sun cause oxidation and this can result in skin cancer. People who eat a very clean diet can and should take at least 15 to 30 minutes of sun a day.

  2. I would interested to see how people in sun-drenched Australia compare to sun-starved Canada, given that both groups have extremely similar lifestyles.

  3. I encourage everybody to carefully read all of Lichtenfeld’s comments about Vitamin D, sun exposure, and cancer reduction on this web site. As a whole, the writing just confuses. He doesn’t say “Edward Giovannucci, D.Sc., M.D.”, he says “A Harvard Researcher.” He doesn’t say “physicians Joe Bob and Mary”, he says “the same authors.” He doesn’t say whether or not there are other groups of physicians whose work agrees with the work done by Giovannucci et al (there are). He doesn’t cite any scientific works in opposition to their recommendations. In other articles, he doesn’t discuss their work as balanced and modest, but in an alarmist mode – “stop people from running to the beaches and getting sunburn.” Duh!

    Don’t stop here at this work of obfuscation – do your own research, make up your own mind. A great place to start is your local library – I’m sure you can find several texts in yours that will provide you with significant scientific information about sunshine, vitamin D, and health improvement (and DON’T just focus on cancer reduction!). Use this as an opportunity to expand your horizon – you CAN’T rely on a single approach to resolve your health issues. Health comes from wise living, not just 15 minutes of sunshine per day (though that kind advice is sound, in my opinion). It DEFINATELY won’t come from a pharmaceutical pill you add to your Standard American Diet. Don’t ultimately rely on the medical industry – they are primarily concerned with their jobs and profits. YOU are the one that is primarily concerned with your health, and the health of your family. Listen to what your doctor has to say, and if it passes muster, heed it. But ALWAYS remember its your decision, not theirs.

    We are the most educated nation on earth – so use your educated mind, and come to your own conclusions.

    Were I to pick one book for you to start with, it would be “The China Study” by T. Colin Campbell. Borrow a copy from your library. By the way, evidence from the study supports modest sun exposure as being good for your health.

    – Dan Radke
    Bethany, OK

  4. I wholeheartedly recommend every American read “The China Study” by T. Colin Campbell. Get educated on the latest GOOD research done on diet and its relationship to health. This book literally changed my whole outlook on the situation. Read it and try to put into practice the changes you feel you are ready to make in your lifestyle that will profoundly decrease your probability of getting cancer or heart disease.

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