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Vitamin D May Boost Colon Cancer Survival, Study Finds


5 Star


Vitamin D May Boost Colon Cancer Survival, Study Finds

Our Review Summary

This story reports the results of research presented at a symposium showing that metastatic colon cancer patients who had higher levels of vitamin D in their blood before undergoing chemo- and biological therapies survived substantially longer on average than similar patients with lower levels of the vitamin. Let’s be clear about this story’s many strengths: It duly noted the long and checkered history of research into the benefits of vitamin D, and that no advanced cancer patient should begin self-medicating with high-dose supplements. It was properly cautious in noting that the study had not yet undergone peer review and publication, and in quoting the investigators and outside experts about the study’s limitations.

With those strengths firmly in mind, we think this story could have done a few things better:

  • Despite stating clearly that this study cannot prove cause and effect, the story confused this issue in a couple of areas. The headline wording (which – we understand – is usually not the reporter’s choice) and introduction strongly suggest that vitamin D may cause cancer patients to live longer, something that conflicts with the story’s subsequent contention that the study can’t prove this. The story also suggests that everyone, including cancer patients,  should in effect get their vitamin D levels checked and take a supplement if low. Though this may make intuitive sense, it simply isn’t supported by any convincing data. This study provides no proof that cancer patients with low vitamin D levels can improve their outcomes by supplementing. Such arguments have been used to recommend a host of other vitamins (C, E, beta carotene, B complex, etc) that have subsequently been shown to provide no benefit and possibly cause harm.
  • The second problem, in our opinion, is that these results are simply too good to be true. The difference in outcomes among those with higher and lower vitamin D levels is quite large–on the order of what a blockbuster cancer-killing drug might achieve. There is simply no reason to believe that vitamin D supplementation would be so potent when known anti-cancer drugs have much more modest benefit. Although the story made a commendable effort to speak with experts who might have offered this perspective, this kind of clear bottom-line assessment unfortunately never made it into the piece. Science is complicated, and sometimes even the best efforts will fall short of what we’d ideally like to see in a story.


Why This Matters

For advanced cancer patients, the possibility that going into treatment with higher but still normal vitamin D levels might extend the time to disease progression by a couple of months on average — and on average extend their lives by  7 to 8 month — is an important piece of news. Unfortunately, the study reported on here wasn’t designed to prove this, and readers of this story might take home some mixed messages about what to do.


Does the story adequately discuss the costs of the intervention?

Not Applicable

This story does not discuss cost. However, most people generally understand that vitamin supplements are affordable, so we’ll rate it not applicable.

Does the story adequately quantify the benefits of the treatment/test/product/procedure?


The story offers a good explanation of the survival benefit observed in the study and puts it in appropriate context. It notes that patients in the highest vitamin D category lived an average of average of 32.6 months, compared with 24.5 months for those in the lowest category. That being said, it would be hard for any reader to clearly understand from this story that the vitamin D levels among the better-surviving patients were still well within the normal range. Even those patients in the “higher” level category averaged just  27.5 nonograms/mililliter on a clinical spectrum that considers 25 to 80 optimal and safe.

Does the story adequately explain/quantify the harms of the intervention?


The story makes it clear that patients should not take supplements to increase vitamin levels if they are already normal, thus preventing harms from oversupplementation. However, we wish the story had specifically mentioned potential side effects of high dose vitamin D.

Does the story seem to grasp the quality of the evidence?

Not Satisfactory

The story notes that the results haven’t yet been published in a journal or undergone rigorous peer review. And it is careful to mention that the results represent an association rather than a cause-and-effect relationship, which is crucial for readers to understand. However, this explanation comes several paragraphs into the story and is at odds with the story’s headline, which states, “Vitamin D May Boost Colon Cancer Survival.” The active language of the headline — “boosts” — clearly indicates a cause-and-effect relationship between vitamin D and cancer survival. And since many readers may not get past the headline, we’re going to rate this unsatisfactory. This study simply shows that individuals with higher vitamin D levels had more favorable outcomes. Even though the researchers controlled for other baseline differences, it isn’t clear whether there is a causal relationship or whether vitamin D levels are simply reflecting something else about the patient’s health. Even if there is a causal relationship, only a study that randomly assigned patients with low vitamin D levels to supplementation or not could show benefit. Finally, readers should understand that these results are simply too good to be true. The amount of benefit associated with higher vitamin D levels in terms of colon cancer related survival are of a magnitude you would expect with a blockbuster cancer killing drug. Even if vitamin D offers some benefit, it is highly unlikely to confer such a blockbuster outcome.

Does the story commit disease-mongering?


Metastatic colorectal cancer is life altering and life threatening at the time of diagnosis. It doesn’t get more serious than that. No mongering here.

Does the story use independent sources and identify conflicts of interest?


The story quotes an outside expert offering an important piece of context and caution about the findings. And it includes a statement from a second outside source with expertise in oncology who underscores the important finding about progression-free survival. Yes!

Does the story compare the new approach with existing alternatives?

Not Applicable

The story could have mentioned how the findings compare with other similar factors — diet quality, exercise, stress reduction etc. — that might have an impact. However, since the evidence on these issues is similarly limited, this criterion is not really applicable

Does the story establish the availability of the treatment/test/product/procedure?

Not Applicable

Most people know that vitamin D supplements are widely available. A brief statement to that effect would have earned the story a satisfactory, as opposed to not applicable.

Does the story establish the true novelty of the approach?


The story does a good job of telling readers that vitamin D has long been studied for its anti-cancer role, and that this new study  merely “adds more weight” to “suspicions” that it might be a valuable cancer-fighting factor.

Does the story appear to rely solely or largely on a news release?


There was a news release issued by the researchers’  institution, but the story had different quotes obviously gleaned from interviews. The story clearly went well beyond the news release.

Total Score: 6 of 7 Satisfactory


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