Vitamin D is necessary for calcium homeostasis, and thus a healthy musculoskeletal system. It is also implicated in contributing to defences against a range of other ailments including autoimmune diseases, respiratory tract infections and cancers. It is not entirely clear how all these benefits are achieved, but not being deficient in vitamin D has a range of health benefits, including observations of less severe outcomes of covid-19 infection.
The body has two sources of vitamin D, by ingestion of food or supplements, and through exposure of unprotected skin to the UVB radiation in sunlight. Sun exposure is the main source for most people as the modern diet does not contain very much vitamin D. However, the availability of sunlight depends very much on location, predominantly latitude, and becomes a limiting factor in vitamin D synthesis as latitude increases. Personal behaviour then influences exposure within a given climate and environment, while personal characteristics, predominantly skin pigmentation, determine the efficiency of that exposure in establishing and maintaining a suitable vitamin D status. At higher latitudes there is a period in the winter part of the year when there is insufficient sunlight duration and intensity to provide any appreciable vitamin D synthesis through normal activities. This so-called vitamin D winter gets longer as latitude increases – in the UK it lasts about 5 months. During the winter vitamin D status declines, and sun exposure in the rest of the year has to rebuild vitamin D status and provide sufficient stores to last through the next winter. We see this seasonal cycle in vitamin D status in the white-skinned population of Manchester, with some people becoming vitamin D deficient in winter. In a skin type V population the seasonal cycle is around a very much lower mean vitamin D status, and the amplitude of the cycle is much smaller with a lot of deficiency observed. This is partly due to the increased pigmentation in type V (brown) skin, but we also found this population spent less time in the sun and exposed less skin for cultural reasons.
The aim of this project is to undertake a similar study in black-skinned (skin type VI) people in the Manchester region. A cohort of volunteers will provide seasonal information on their sun exposure (through UV dosimetry and exposure diaries), dietary intake (food questionnaire), and vitamin D status (blood sample analysed for 25-hydroxyvitamin D), for a period of one year (4 seasonal sampling weeks). The results can be directly compared with data from the previous work in other skin types, providing a better understanding of vitamin D status, and its annual cycle, in this element of the population. It will determine the level of vitamin D deficiency in the black-skinned population, provide indications of the dominant reasons for any deficiency and thus indicate mitigating measures that can best be taken to avoid deficiency.
This will inform more nuanced public health policies on sun protection/sun exposure, accounting for skin pigmentation in addressing the opposing risks of skin cancer and vitamin D deficiency on the overall health of the population. In turn this can help address health inequalities and lead to an improvement in several aspects of health across all skin types, as each has tailored advice appropriate to their skin pigmentation.
To be sent to Professor Ann Webb: email@example.com
To apply please make an application online here - https://www.manchester.ac.uk/study/postgraduate-research/admissions/how-to-apply/
Please search and select 'PhD Environmental Science' for programme and ' PhD Environmental Science' for plan.