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Dear Dr Cannell: Sunlight, vitamin D and the prevention of cancer

Posted on: November 5, 2012   by  John Cannell, MD


Dear Dr. Cannell:

Making vitamin D through sun exposure is the natural way to maintain D levels as shown through hundreds of thousands of years of human history. I analyzed a paper on about 50 studies of various internal cancers and their relationship to vitamin D, latitude, and sun exposure. Most of the analysis was focused on four cancer types: breast, colon, prostate and lymphoma. Overall van der Rhee concluded that while vitamin D levels/supplementation was only consistently associated with a decrease in colon cancer, sun exposure was consistently associated with a decrease in all four cancers.

van der Rhee H, Coebergh JW, de Vries E. Sunlight, vitamin D and the prevention of cancer: a systematic review of epidemiological studies. Eur J Cancer Prev. 2009 Nov;18(6):458-75

I took it a step further by quantifying the percentage of studies that found a significant decrease in cancer as reported by van der Rhee.

  • Sunlight and latitude studies: 77.1% show significant correlation
  • Vitamin D level studies: 63.4% show significant correlation
  • Diet or supplementation studies: 47.4% show significant correlation

I do acknowledge that many vitamin D supplementation studies are flawed in that the amount given are not high enough to show D’s full potential. However, let’s face it, the present results of vitamin D studies, particularly those dealing with supplementation, show that people are not getting enough sun to maintain optimal levels.

I can’t tell you how many times articles about studies finding significant association between sun exposure and decreased risk of a serious condition ends with a call to study vitamin D supplementation rather than studying UV exposure, including sunbeds. Something obvious is being missed or deliberately avoided due to the politically incorrectness of advocating intentional UV exposure due to the potential risk of skin cancer, one of the conditions least likely to kill you.

Dr. Cannell, I know you have an incredible drive to get to and report the truth. I hope you will take a good look at this issue and, if you concur, help focus attention on the advantages of making vitamin D over taking vitamin D.


John, New York

Dear John:

I couldn’t agree more, virtually every epidemiological study of vitamin D levels, latitude, sunlight hours, temperature, or outdoor activity, and there are thousands, is actually studying the benefits of sun exposure. As van der Rhee says, “It might therefore be more appropriate to speak of the ‘sunlight hypothesis’ instead of the ‘vitamin D hypothesis.’”

We know that sensible sunlight is good for humans. As I have blogged on before, those who avoid the sun are putting themselves at risk. In addition, the use of low-pressure sunbeds in the winter is a practice I endorse and one that I use myself. In fact, the increase of skin cancer incidence has coincided during the thirty years of the sun scare.

However, for the health of the millions of Americans who bought into the sun and sunbed scare, I can only wait for upcoming randomized controlled trials of significant amounts of daily vitamin D. I doubt many studies of daily doses of 5,000 IU will be negative, depending on what disease is being studied, but sunshine (and sunbeds that replicate sunlight) should be immediately studied for their apparent additional health benefits. Avoiding sunshine is a form of hubris, excessive pride and arrogance, and those who do it should proceed at their peril.

John Cannell, MD

2 Responses to Dear Dr Cannell: Sunlight, vitamin D and the prevention of cancer

  1. [email protected]

    Dear Dr. Cannell,

    1. Is it true that taking a hot shower after sun/tanning bed exposure will wash away a valuable portion of the Vit. D precursors that have been created in the skin? If so, how long should one wait.

    2. Does supplementary Vit. D need to be taken with food for maximum absorption.


  2. clubtan

    Hubris! there “is” a word that explains the insanity! thanks!

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