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ABSTRACT
Public health authorities in the United States are recommending that men, women and children reduce their exposure to sunlight, based on concerns that this exposure will promote skin cancer. On the other hand, data show that increasing numbers of Americans suffer from vitamin D deficiencies and serious health problems caused by insufficient sun exposure. The body of science concerning the benefits of moderate sun exposure is growing rapidly, and is causing a different perception of sun/UV as it relates to human health. Melanoma and its relationship to sun exposure and sunburn is not adequately addressed in most of the scientific literature. Reports of favorable health outcomes related to adequate serum 25(OH)D concentration or vitamin D supplementation have been inappropriately merged, so that benefits of sun exposure other than production of vitamin D are not adequately described. This review of recent studies and their analyses consider the risks and benefits of sun exposure which indicate that insufficient sun exposure is an emerging public health problem. This review considers the studies that have shown a wide range health benefits from sun/UV exposure. These benefits include among others various types of cancer, cardiovascular disease, Alzheimer disease/dementia, myopia and macular degeneration, diabetes and multiple sclerosis. The message of sun avoidance must be changed to acceptance of non-burning sun exposure sufficient to achieve serum 25(OH)D concentration of 30 ng/mL or higher in the sunny season and the general benefits of UV exposure beyond those of vitamin D.
Abbreviations
| 5(OH)D | = | 25-hydroxyvitamin D |
| BCC | = | basil cell carcinoma |
| CI | = | confidence interval |
| CVD | = | cardiovascular disease |
| HR | = | hazard ratio |
| IU | = | international units |
| MS | = | multiple sclerosis |
| NMSC | = | non-melanoma skin cancer |
| ng/mL | = | nanograms per milliliter |
| NHL | = | non-Hodgkins lymphoma |
| OR | = | odds ratio |
| RR | = | relative risk |
| SCC | = | squamous cell carcinoma |
| UVR | = | Ultraviolet Radiation (290–400 nm) |
| UVA | = | Ultraviolet-A (316–400 nm) |
| UVB | = | Ultraviolet-B (290–315 nm) |
Disclosure of potential conflicts of interest
No potential conflicts of interest were disclosed.
ORCID
Michael F. Holick http://orcid.org/0000-0001-6023-9062
Notes
a The 2010 Institute of Medicine vitamin D report defined vitamin D deficiency as serum 25(OH)D levels of less than 12ng/mL and vitamin D insufficiency as serum 25(OH)D levels of less than 20 ng/mL.Citation2 NHANES data for 2001–2006 show that 8% of Americans had 25(OH)D below 12 ng/mL and 32% had 25(OH)D below 20 ng/mL.Citation3
b According to the Centers for Disease Control and Prevention, the prevalence of sunburns increased from 32% of all adults in 1999 to 34% in 2004Citation35 and up to 50% in 2012.Citation36 Among adolescents aged 12–18 in 1999, 83% reported at least one sunburn in the previous summer and 36% reported three or more sunburns in the previous summer.Citation37
c Data on temporal trends in vitamin D levels are contained in study by Ginde et al. 2009Citation38 who reported that NHANES data on serum 25(OH)D levels show that the prevalence of 25(OH)D of less than 10 ng/mL increased from 2% in 1988–1994 to 6% in 2001–2004 while over the same time period the prevalence of 25(OH)D of less than 20 ng/mL increased from 22% to 36%, and for 25(OH)D of less than 30 ng/mL increased from 55% to 77%.
d Such an explanation is not new. White et al. 1988Citation39 (published as Garland et al. 1990Citation40) proposed that low levels of vitamin D (either locally available in skin or circulating in plasma) allow melanomas which were previously initiated by sunlight exposure to develop into clinically apparent disease in continually sunlight deprived individuals. This proposal was apparently ignored as precautions against melanoma focused on sun avoidance and liberal use of chemical sunscreens, with inadequate attention paid to the role of sunburns in melanomagenesis and to the role of vitamin D in inhibiting cancer. The first cancer cell line shown in 1980 to be inhibited in growth by 1,25(OH)2D was in fact a melanoma cell line. In 1989 Gallagher et al.Citation41 suggested that part of the increased incidence in melanoma could be attributed to the decline in outdoor workers.
e Sunscreens are intended to prevent sunburn when used in thickness and frequency recommended by manufacturers or used in setting SPFs. However, studies have shown that the incidence of sunburn is higher or the same in people who almost always use sunscreens compared with those who rarely use sunscreens.Citation43-45
f The differences between NHANES III and NHANES 2001- 2004 may be attenuated by approximately 4 ng/mL after adjustment for improvements in the serum 25(OH)D assay performance from NHANES III to NHANES 2001-2004.Citation71
g The Endocrine Society's 2012 review of the nonskeletal effects of vitamin D also found there was insufficient evidence to support a role of vitamin D supplementation in correcting vitamin D insufficiency.Citation66
h There are 6 categories of skin on the Fitzpatrick Scale: Type I Very Fair White - always burns, never tans;Type II Fair White - usually burns, tans minimally; Type III Cream White – sometimes mild burn, gradually tans; Type IV Brown – rarely burns, tans with ease; Type V Dark Brown – very rarely burns, tans very easily; Type VI Black – never burns, tans very easily.