Sunday, July 14, 2013

Sunscreen {protection methods}

Sunscreen is one of many ways we can protect ourselves from the sun, but it's not the only way.  Shade, long sleeves, and hats also work well in protecting us.  I was surprised to learn that people who tend to seek shade and wear long sleeves where more likely to be vitamin D deficient than people who reported regularly using sunscreen (1).  Part of the reason this surprised me is that for years I've thought in the back of my head that sunscreen was greatly contributing to the epidemic of vitamin D deficiency, but inasmuch as my reading has shown me, this is probably not the case.  

The CDC started The National Health and Nutrition Examination Survey (NHANES) in the early 1960's to conduct nation-wide surveys to gather statistics of various population groups and health topics.  In 1999 the program became an ongoing survey that examines about 5,000 people each year regarding emerging health and nutrition topics.   The data NHANES collects is available for researchers to analyse and use, or for agencies to utilize in evaluating and implementing health policy.  One example of NHANES data in use is the growth charts that doctors use to see how well babies and children are growing (2).

Between 2003-2006 NHANES collected data regarding sun protection habits and the levels of vitamin D in participants' blood.  Linos, et al., analysed this data and published a paper examining what they found (1).  Below is a graph from their paper that illustrates part of what they found-- that for all races combined, two factors, staying in the shade and wearing long sleeves, were significantly associated with lower vitamin D levels, while frequency of wearing hats or using sunscreen were not associated with lower vitamin D levels.

The NHANES data is a survey intended to gather information about the population at a specific point in time--this study design is called a cross-sectional study.  Cross-sectional studies are the simplest of all study designs, but also one of the weakest(3).  This type of study is often used to asses prevalence; for example, in this paper the authors measured the prevalence of vitamin D deficiency in different subsets of the population.  The major weakness of this design, however, is that because of the lack of any time dimension (all data is gathered at the same time) it is extremely difficult to establish any semblance of causality (3).  Because of this major design limitation we need to be careful not to make too strong of a conclusion from this study.

I think what they found is interesting-- I wouldn't have guessed that sunscreen was not associated with  vitamin D deficiency, but that shade and long sleeves were associated.  Although we certainly can not say that shade and long sleeves cause deficiency it is instructive to consider this association when thinking about our sun protection options.  We should realize that it's possible that protective clothing may be much more effective at protecting us from the sun than sunscreen-- this may be good or bad depending on what your goals are.

Although causality can't be established by this study, I still think it makes a fairly strong case that sunscreen is not single-handedly causing the epidemic of vitamin D deficiency.  For me, I think this means that I'll worry less about using sunscreen, but also that in certain situations I'll be more likely to seek shade, since that is apparently one good way to protect myself from overexposure to the sun.

Photo Credit: Sanny Hauck


(1)Linos E., et al.. Sun protective behaviors and vitamin D levels in the US population: NHANES 2003-2006. Cancer Causes Control. 2012 Jan;23(1):133-40. doi: 10.1007/s10552-011-9862-0. Epub 2011 Nov 2. Accessed on 7/9/13.  
(2) National Center for Health Statistics.  National Health and Nutrition Examination Survey 2013-2014 Overview: Let's Improve Our Health. Accessed on 7/11/2013
(3) Elwood, M. Critical Appraisal of Epidemiological Studies and Clinical Trials: Third Edition. Oxford: Oxford University Press, 2008.  p. 25-6, 46. 

No comments: