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The Institute of Medicine did not find the vitamin D–cancer link because it ignored UV-B dose studies

Published online by Cambridge University Press:  01 April 2011

William B. Grant
William B. Grant*
Affiliation:
Sunlight, Nutrition, and Health Research Center (SUNARC), PO Box 641603, San Francisco, CA 94164-1603, USA Email: [email protected]
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Abstract

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Type
Letters to the Editor
Information
Public Health Nutrition , Volume 14 , Issue 4 , April 2011 , pp. 745 - 746
Copyright
Copyright © The Author 2011

Madam

When The Institute of Medicine (IOM) of the National Academies released its new Dietary Reference Intakes for Calcium and Vitamin D report on 30 November 2010(1, Reference Ross, Manson and Abrams2), the vitamin D research community was shocked and dismayed at the findings. The committee found a benefit only for bones, leading to the finding that a 25-hydroxyvitamin D (25(OH)D) level of 20 ng/ml was adequate and a recommended intake of 15 μg/d for most people. These are well below the recommendations of vitamin D experts: intakes of up to 50 μg/d and achieving serum 25(OH)D levels of 40–60 ng/ml(3). Casual solar UV-B irradiance in summer in England raises serum 25(OH)D levels by nearly 40 nmol/l, equivalent to the production of about 37.5 μg/d for those aged 45 years(Reference Hyppönen and Power4), far more than suggested by the IOM(1).

The UV-B–vitamin D–cancer hypothesis was based on an ecological study of the geographical variation of colon cancer mortality rates and sunlight doses in the USA(Reference Garland and Garland5) and has been extended by subsequent ecological studies in Australia, Asia, Europe and the USA to about twenty types of cancer(Reference Grant and Garland6–Reference Grant and Mohr9). While the IOM considered some ecological studies as background information, it noted they have the primary weakness that ‘Outcome measures are not predictable at the individual level’ and, thus, are of low quality for dietary reference intakes(1). This summary dismissal is not warranted: in part because no mechanism other than production of vitamin D has been proposed to explain the ecological study findings, in part since the findings of ecological studies of cancer have been supported by other studies(Reference Grant10), and in part since ecological studies integrate the effect of UV-B and vitamin D over much of the lifetime and include many cases.

A second type of study based on solar UV-B is that of cancer risk with respect to diagnosis or death from non-melanoma skin cancer (NMSC). The primary risk factor for NMSC is UV irradiance, with UV-B the most important risk factor for NMSC death(Reference Grant11). An ecological study for Spain found fifteen types of cancer inversely correlated with NMSC mortality rate after adjusting for smoking(Reference Grant12). A record linkage study found significant inverse correlations between diagnosis of NMSC and incidence of gastric, liver, pancreatic and prostate cancer and non-significant inverse correlations for five other types of cancer(Reference Tuohimaa, Pukkala and Scelo13). A reduced risk of prostate cancer incidence was noted with more early-life UV-B irradiance(Reference John, Koo and Schwartz14).

A third type of study is based on solar UV-B exposure related to occupation. A death certificate-based case–control study of cancer mortality rates in the USA found significant inverse correlations for breast and colon cancer with respect to occupations with high occupational exposure to sunlight(Reference Freedman, Dosemeci and McGlynn15). A study of cancer risk in Rhineland-Palatinate, Germany found significantly reduced risk of nearly a dozen types of internal cancer compared with incidence of NMSC plus melanoma in regions with more land devoted to winegrowing(Reference Seidler, Hammer and Husmann16, Reference Grant17).

A fourth type of study is the case–control study using self-reported personal sun exposure. A pooled study of this nature found a protective effect of recreational sun exposure at 18–40 years of age and in the 10 years before diagnosis for non-Hodgkin's lymphoma(Reference Kricker, Armstrong and Hughes18).

Together with other studies such as case–control studies of vitamin D and breast cancer(Reference Yin, Grandi and Raum19) and improved survival rate after diagnosis of non-Hodgkin's lymphoma and other types of cancer with higher serum 25(OH)D at time of diagnosis(Reference Drake, Maurer and Link20), there is strong support for a causal relationship between vitamin D and reduced risk of cancer(Reference Grant10) which could have permitted the IOM to find a beneficial effect of vitamin D in reducing the risk of cancer.

Disclosure

I receive or have received funding from the UV Foundation (McLean, VA, USA), the Sunlight Research Forum (Veldhoven, The Netherlands), Bio-Tech-Pharmacal (Fayetteville, AR, USA), the Vitamin D Council (San Luis Obispo, CA, USA) and the Danish Sunbed Federation (Middelfart, Denmark).

References

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