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Newsworthy vitamin D research, accurately and cautiously explained by the American Cancer Society

Large international study links blood vitamin D levels to colorectal cancer risk

Our Review Summary

This news release describes an analysis of data from 17 different studies where blood levels of vitamin D were reported. The main finding: higher circulating vitamin D levels are associated with lower risk of colorectal cancer.

The release provides a careful and appropriately cautious overview that explains why the study is newsworthy. This document should set the stage for balanced and informative coverage from news organizations. A few minor improvements — such as mentioning specific limitations that affect the conclusions that can be drawn from this type of analysis — would’ve improved the message even further.


Why This Matters

This is an important study by some of the nation’s top vitamin D researchers. Its findings have the potential to impact recommendations concerning Vitamin D supplementation.

It’s worth keeping in mind, however, that there is a growing mountain of research on the effects of Vitamin D, some of it positive and some of it negative, and that any recommendation related to what are considered “optimal” concentrations should be made in the context of all that research, not just its apparent effects in one particular organ system.


Does the news release adequately discuss the costs of the intervention?

Not Applicable

This release is not reporting on vitamin D supplementation but about circulating levels of vitamin D in the body. Although some readers may not make this distinction, cost is not strictly applicable here and we won’t penalize the release for not mentioning it.

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

Not Satisfactory

Benefits are only presented in relative terms — not absolute numbers. For example: “those with deficient concentrations of vitamin D had a 31% higher risk of colorectal cancer during follow-up, which averaged 5.5 years (range: 1 – 25 years). Similarly, concentrations above bone health sufficiency were associated with a 22% lower risk.”

While that’s not good enough for a satisfactory rating, we acknowledge that it would probably be quite difficult to provide absolute risk reduction figures based on these data. And the release does provide the lifetime absolute risk of colon cancer in men (4.5%) and women (4.2%) — which helps contextualize the 22% relative reduction associated with higher vitamin D levels.

To meet our standard, however, the release should have attempted to provide some clarity on what that 22% reduction might indicate in terms that are actually meaningful for readers. In other words, if my lifetime risk of colorectal cancer is 1 out of 22 (the rate given for men in the news release), how might a 22% reduction change that risk?

Does the news release adequately explain/quantify the harms of the intervention?


The news release indicates that vitamin D should ideally be obtained from the diet, and that there are no known harms to eating foods with vitamin D (an exception being when a mishap caused over-fortification of a local milk supply a few decades ago). Skin cancer risk associated with sun exposure was covered appropriately.

Does the news release seem to grasp the quality of the evidence?


The evidence is explained with sufficient care for a layperson to understand exactly what was being compared, with the exception of the actual vitamin D levels reported.  More specifics on that would have been very helpful.

The release is also careful not to use cause-and-effect language to describe the results — which would be inappropriate for this kind of study.

Furthermore, the release is appropriately circumspect about the implications of the new results, stating that “health agencies do not recommend vitamin D for the prevention of colorectal cancer,” and that the study “adds new information that agencies can use when reviewing evidence for vitamin D guidance.”

The release would have been improved with a discussion of limitations that affect the conclusions we can draw from this type of study. For example, might people with higher vitamin D levels differ from those with lower levels in important ways (e.g. diet, exercise, socioeconomic status, etc) that impact cancer risk? If so, the effects attributed to vitamin D might actually be the result of some other factor.

Does the news release commit disease-mongering?


There is no obvious disease mongering here. In fact, numbers of incident cases and deaths in the US expected in 2018 are given for accuracy and to anchor the discussion. Well done.

Does the news release identify funding sources & disclose conflicts of interest?


Vitamin D supplement manufacturers appeared to play no role in the analysis, and the funders are from the American Cancer Society, the Harvard T.H. Chan School of Public Health, and the U.S. National Cancer Institute.

Does the news release compare the new approach with existing alternatives?

Not Satisfactory

The release mentions the types of food (and sunlight) where one obtains Vitamin D, which is useful information.

However, the benefit addressed by the release is the prevention of colorectal cancer, and a brief mention of other approaches to reducing risk for this cancer would have been appropriate. The only proven approaches to reducing deaths from colorectal cancer are screening via a stool test or endoscopy.

Does the news release establish the availability of the treatment/test/product/procedure?

Not Applicable

Supplements, vitamin D-containing foods, and sunlight are pretty much available everywhere.

Does the news release establish the true novelty of the approach?


There are no unwarranted claims to novelty here and it is pretty clear that this is a subject that has a fairly long history of research.

The release also makes it clear what was new about the latest study compared to previous research. For example:

A single, widely accepted assay and laboratory was used for new vitamin D measurements and calibration of existing vitamin D measurements. “In the past, substantial differences between assays made it difficult to integrate vitamin D data from different studies,” explained Regina G. Ziegler, PhD, a National Cancer Institute epidemiologist and co-senior author on the article. “This calibration approach enabled us to systematically explore risk over the broad range of vitamin D levels seen internationally.”

Total Score: 6 of 8 Satisfactory

Comments (1)

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Mark McConnell

June 25, 2018 at 11:54 am

I do not find this newsworthy at all. This is simply another report that “healthy people are healthy”. I gives not information on what patients and doctors should do. All the randomized trials of vitamin D supplementation, to my knowledge, are negative to date.