Advice vs Real Life: How Do Sun-Safe Practices Affect Vitamin D Levels?
Vitamin D is one of those confusing nutrients. It is hard to consume adequate vitamin D from the diet, and sun exposure can make up for this shortfall. Yet, sun exposure increases risk of skin cancer. Advice to reduce exposure to the sun could therefore concurrently decrease risk of skin cancer while increasing the likelihood of vitamin D deficiency. To make matters more confusing, studies show that behaviors such as wearing sunscreen do not necessarily result in lower sun exposure (Linos). Following sun-safe behaviors may actually increase risk of skin cancer, as they help people avoid particularly nasty short-term consequence of sun exposure (sunburn), and encourage them be outside in the sun for longer. The net effect of sun-safe behaviors on both vitamin D levels and risk of skin cancer depends on whether changes in behavior lead to an increase in time spent in the sun, and the effectiveness of the measures.
To investigate this relationship further, Hansen and co-workers looked at whether particular sun-safe measures affected the circulating vitamin D levels of Danish residents. This was part of the StatusD study: measurements were conducted on 3194 adults and children aged between 2 and 69 years of age living in three areas of Denmark.
The four sun exposure guidelines were: seek shade, wear a sunhat, wear protective clothing, and use sunscreen. Blood samples were taken in both Spring and Autumn, representing the nadir and peak of vitamin D levels in the blood. Subjects completed various questionnaires that asked about general demographics and health-related behaviors such as smoking and levels of physical activity.
The authors found that the behaviors “seek shade” and “wear protective clothing” were significantly associated with lower vitamin D concentrations in adults, and the number of guidelines followed was associated with reduced vitamin D concentrations. Wearing either sunscreen or a sunhat was not associated with vitamin D concentrations. In addition, the greater the number of sun-safe guidelines followed, the greater the risk of deficiency (<25 nmol/l vitamin D) or insufficiency (<50 nmol/l vitamin D).
This study shows that some sun-safe behaviors result in lower circulating vitamin D levels, but others do not. Although all four sun-safe behaviors will in theory reduce the amount of sun exposure to the skin, the fact that both sunscreen and sunhats are intended to protect people while in the sun may mean that these two behaviors may encourage people to spend more time in the sun that they would otherwise be able to tolerate. On the other hand, sitting in the shade on a sunny day rather than in the sun is likely to reduce overall sun exposure. Wearing long-sleeved clothing on a hot, sunny day may seems counter-intuitive to many people who prefer to strip off when the mercury climbs, and this is reflected in a low proportion of the study population reporting that they follow this guideline, however wearing more clothing may actually encourage people to seek shade or go indoors when it is hot.
This study confirms that some sun-safe behaviors reduce circulating vitamin D levels. But is it a good idea to relax recommendations to keep out of the sun to prevent vitamin D deficiency? Lin and colleagues point to increases in population mortality when UV exposure increases. It would be interesting to see a study modelling the effect of sun-safe behaviors, vitamin D concentrations and mortality. There is, however, another way to maintain adequate vitamin D that does not carry a risk of skin cancer or skin aging: dietary supplements. With supplements, it is possible to get enough vitamin D without sun exposure.
Hansen, L.; Tjønneland, A.; Køster, B.; Brot, C.; Andersen, R.; Lundqvist, M.; Christensen, J.; Olsen, A. Sun Exposure Guidelines and Serum Vitamin D Status in Denmark: The StatusD Study. Nutrients 2016, 8, 266. http://www.mdpi.com/2072-6643/8/5/266
Hughes MC, Williams GM, Baker P, Green AC. Sunscreen and prevention of skin aging: a randomized trial. Ann Intern Med. 2013 Jun 4;158(11):781-90. doi: 10.7326/0003-4819-158-11-201306040-00002. http://www.ncbi.nlm.nih.gov/pubmed/23732711
Lin SW, Wheeler DC, Park Y, Spriggs M, Hollenbeck AR, Freedman DM, Abnet CC. Prospective study of ultraviolet radiation exposure and mortality risk in the United States. Am J Epidemiol. 2013 Aug 15;178(4):521-33. doi: 10.1093/aje/kws589. Epub 2013 Jul 17. http://www.ncbi.nlm.nih.gov/pubmed/23863757
Linos E, Keiser E, Kanzler M, Sainani KL, Lee W, Vittinghoff E, Chren MM, Tang JY. 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. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3718293/
Victor L. Fulgoni III, Debra R. Keast, Regan L. Bailey, and Johanna Dwyer. Foods, Fortificants, and Supplements: Where Do Americans Get Their Nutrients? J. Nutr. 2011 jn.111.142257; first published online August 24, 2011. doi:10.3945/jn.111.142257 http://jn.nutrition.org/content/early/2011/08/26/jn.111.142257.full.pdf+html