Optimal Sunscreen Use, During a Sun Holiday With a Very High Ultraviolet Index, Allows Vitamin D Synthesis Without Sunburn

A.R. Young; J. Narbutt; G.I. Harrison; K.P. Lawrence; M. Bell; C. O'Connor; P. Olsen; K. Grys; K.A. Baczynska; M. Rogowski-Tylman; H.C. Wulf; A. Lesiak; P.A. Philipsen

Disclosures

The British Journal of Dermatology. 2019;181(5):1052-1062. 

In This Article

Abstract and Introduction

Abstract

Background: Sunlight contains ultraviolet (UV)A and UVB radiation. UVB is essential for vitamin D synthesis but is the main cause of sunburn and skin cancer. Sunscreen use is advocated to reduce the sun's adverse effects but may compromise vitamin D status.

Objectives: To assess the ability of two intervention sunscreens to inhibit vitamin D synthesis during a week-long sun holiday.

Methods: The impact of sunscreens on vitamin D status was studied during a 1-week sun holiday in Tenerife (28° N). Comparisons were made between two formulations, each with a sun protection factor (SPF) of 15. The UVA-protection factor (PF) was low in one case and high in the other. Healthy Polish volunteers (n = 20 per group) were given the sunscreens and advised on the correct application. Comparisons were also made with discretionary sunscreen use (n = 22) and nonholiday groups (51·8° N, n = 17). Sunscreen use in the intervention groups was measured. Behaviour, UV radiation exposure, clothing cover and sunburn were monitored. Serum 25-hydroxyvitamin D3 [25(OH)D3] was assessed by high-performance liquid chromatography–tandem mass spectrometry.

Results: Use of intervention sunscreens was the same (P = 0·60), and both equally inhibited sunburn, which was present in the discretionary use group. There was an increase (P < 0·001) in mean ± SD 25(OH)D3 (28·0 ± 16·5 nmol L−1) in the discretionary use group. The high and low UVA-PF sunscreen groups showed statistically significant increases (P < 0·001) of 19·0 ± 14·2 and 13·0 ± 11·4 nmol L−1 25(OH)D3, respectively with P = 0·022 for difference between the intervention sunscreens. The nonholiday group showed a fall (P = 0·08) of 2·5 ± 5·6 nmol L−1 25(OH)D3.

Conclusions: Sunscreens may be used to prevent sunburn yet allow vitamin D synthesis. A high UVA-PF sunscreen enables significantly higher vitamin D synthesis than a low UVA-PF sunscreen because the former, by default, transmits more UVB than the latter.

Introduction

Terrestrial solar ultraviolet radiation (UVR ~295–400 nm) contains UVB (280–315 nm) and UVA (315–400 nm). The maximal UVB content is ~5% but this region is three to four orders of magnitude more damaging than UVA per unit dose (J m−2) for sunburn,[1] potentially mutagenic epidermal DNA lesions, such as cyclobutane pyrimidine dimers (CPDs),[1] and keratinocyte cancers.[2]

However, UVB initiates cutaneous vitamin D3 synthesis. Indeed, most vitamin D (about 80%) is acquired from solar exposure,[3] resulting in seasonal variations in temperate climates.[3,4] Vitamin D is essential for skeletal integrity and has been associated with many other health benefits, although these remain controversial[5] or disputed.[6] It also enhances the repair of epidermal DNA photolesions.[7]

Solar UVR is responsible for an increasing incidence of melanoma, basal cell carcinoma and squamous cell carcinoma (SCC), particularly in white-skinned populations,[8–10] for whom sunburn is a risk factor.[11,12] Much public health effort has been spent advising those at risk to minimize solar UVR exposure. The use of sunscreens is one approach, and there is evidence from randomized trials that sunscreens inhibit SCC,[13] actinic keratosis (a surrogate risk marker for SCC)[14] and melanoma.[15] The role of sunscreens in melanoma prevention has also been supported by large population-based studies.[16,17] However, sunscreen use may impact vitamin D status. Reviews report that different studies reach different conclusions.[18,19] There is a consensus that typical suboptimal sunscreen use probably has a limited effect on vitamin D production.

The sun protection factor (SPF) of a sunscreen is a quantitative measure of its ability to inhibit erythema. Regulatory authorities specify many requirements for SPF determination, one of which is an application thickness of 2 mg cm−2.[20] However, people typically apply much less, for example 0·8 mg cm−2, with a commensurate reduction in SPF.[21,22] Furthermore, application is often patchy with, for example, missing facial coverage.[23] Additionally, people use sunscreens to prolong their intentional solar exposure time.[24,25]

The SPF primarily quantifies protection from UVB, because this waveband is much more erythemogenic than UVA.[1] However, regulatory bodies require UVA protection, the definition of which varies with regional domain.[20] This UVA protection factor (PF) is typically a qualitative index that describes the spectral profile of the sunscreen. One de facto consequence of increased UVA protection is a decrease in UVB protection for a given SPF. This would be expected to have a beneficial effect on vitamin D synthesis.

Holidays result in a highly significant enhancement of vitamin D3 status in adults[26] and children.[27] However, this was accompanied with a high level of sunburn in adults in Tenerife.[28] In both adults and children there were also very high levels of epidermal CPDs, which are a determining event for skin cancer. Sunscreen use can inhibit CPDs,[29] even with very high UVR doses when applied at a typical user application thickness (e.g. 0·75 mg cm−2).[30] It is therefore important to determine conditions of sun exposure that maximize benefit and minimize risk.

The primary aim of this investigation was to assess the ability of two sunscreens to inhibit 25-hydroxyvitamin D3 [25(OH)D3] synthesis during a week-long sun holiday in Tenerife. The study was designed to compare these sunscreens (intervention groups) under optimal use with typical sunscreen use (discretionary group). The secondary aim was to determine whether the different optical properties of the intervention sunscreen would affect 25(OH)D3 synthesis. This was done by formulating two SPF 15 sunscreens with different levels of UVA protection. The hypothesis under test was that the sunscreen with high UVA-PF (by default more UVB transmission) would enable better 25(OH)D3 synthesis than the product with low UVA-PF. We have previously reported that sunscreen intervention in the same participants inhibited erythema. In contrast, there was marked erythema with discretionary sunscreen use.[31]

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