Title: Modelling approach to determine the duration and intensity of sunlight exposure required to maintain and achieve adequate vitamin D status in winter in ‘at risk’ population groups.
Funder: Department of Health (England)

Abstract: Background – the UK’s current nutritional guidelines assume that from school age to retirement, vitamin D requirements are met by skin exposure to UVB in sunlight. It is well documented that at latitudes such as the UK there is insufficient sunlight in winter to synthesise appreciable vitamin D, and vitamin D levels fall from autumn to early spring. To maintain year-round adequate supply of vitamin D through sun exposure alone therefore requires a sufficiently high vitamin D status to be reached in summer to last throughout the winter months. The main determinants of quantity of vitamin D synthesis in skin are: available UVB, exposure time and pattern, skin area exposed, skin pigment and age. Given the diversity of the UK population, the latitudinal gradient, and modern lifestyles, is it valid to assume vitamin D requirements can be met by sun exposure? Moreover, with suggestions that vitamin D requirements are higher than previously supposed, can enough vitamin D be synthesised without risking the negative health impacts of over-exposure? Aims – i) Use a modelling approach to determine the duration and intensity of sunlight exposure required to maintain and achieve adequate vitamin D status in winter in ‘at risk’ population groups; ii) Determine if there is a minimal risk sunlight exposure with respect to skin damage that enables vitamin D production. Research plan and methods of investigation – this is a modelling study with empirically defined inputs based on climatological measurements and a series of previous and ongoing prospective cohort studies. We will use a well-established radiative transfer model to map the available UVB across the UK throughout the year, first for clear skies (best case scenario) and then modified by climate indicators and solar UV measurements. In earlier work we identified behavioural norms and exposures of white Caucasian/South Asian, teenage/adult and photosensitive cohorts to available sunlight, and can therefore model expected exposures across the UK. We also know from our controlled exposure studies how much vitamin D is synthesised per dose of UVB in adults of white Caucasian/South Asian/Black Afro-Caribbean skin types. This enables us to calculate the expected end result of exposures in terms of circulating 25-hydroxyvitamin D (25(OH)D; the measure of vitamin D status) for diverse population sectors, across the UK. Thus, we can estimate whether achieved summer vitamin D status is enough to maintain sufficient vitamin D levels through the winter – based on evidence from our prior work. Our data also permits evaluation of relationships between UVB threshold dose for induction of epidermal DNA damage and vitamin D production, in different skin types. We will consider whether the necessary exposure for adequate vitamin D synthesis is achievable (availability of sunlight), viable (in a modern society) and safe (risks from UVB exposure) for different sectors of the population. Research team – successful group of internationally respected experts from atmospheric sciences (Dr Webb), dermatology-photobiology (Rhodes), endocrinology-biochemistry (Berry), UV-induced mutagenesis (Cooke) with expert statistical support (Vail), and public engagement experience (Rhodes, Farrar). The Manchester team have proven ability to produce pragmatic, application-driven results on sun exposure and vitamin D synthesis, and have ongoing funded collaboration with Cooke, Leicester, quantitatively assessing UV-induced DNA damage alongside vitamin D production. Potential impact/influence on the relevant policy field, users and wider stakeholders – this research is specifically designed to inform the SACN’s risk assessment on Vitamin D and Health to inform dietary reference values for the population, and will provide all necessary information with the requisite speed. It has wider implications in that the methods and model will be adapatable and can be applied to any location, giving the tools developed a global application.


Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING;3.1 PRIMARY PREVENTION INTERVENTIONS TO MODIFY BEHAVIOURS OR PROMOTE WELL-BEING
Health categories: MUSCULOSKELETAL;INFLAMMATORY AND IMMUNE SYSTEM;METABOLIC AND ENDOCRINE;SKIN