Age-related Ability to Synthesise Vitamin D in the Skin on Exposure to Sunlight

  • Oktawia Borecka

Student thesis: Phd


Thesis Abstract Vitamin D and its metabolites are produced following ultraviolet radiation (UVR) exposure of skin precursor 7-dehydrocholesterol (7DHC). The downstream pathway includes classical derivatives 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH)2D), and 24,25-dihydroxyvitamin D (24,25(OH)2D) produced by an alternative pathway. Vitamin D is also sourced through diet. A previous study reported that lower skin 7DHC occurs with age, but there were limitations of the research, and little is also known about the behaviours influencing vitamin D in older age. This project is designed to test the hypothesis that older people have decreased capacity to produce vitamin D due to a lower concentration of 7DHC in their skin compared to younger individuals. The first aim was to develop and validate a high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) method for quantification of 7DHC in human skin. Human skin punch biopsies were obtained through the Manchester Skin Health Biobank. 7DHC was extracted with ethyl acetate:methanol 1:1 (v/v) and derivatised using 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), to allow for improved ionisation through electrospray ionisation mass spectrometry with inclusion of solid supported liquid extraction. This modern assay satisfied research standards for method validation, allowing for detection and quantification of 7DHC in small samples of human skin (0.2 cm2 surface area). The second aim was to evaluate if skin 7DHC concentration differs between younger and older adults, and examine the impact of solar simulated UVR (SSR) on skin 7DHC and serum vitamin D3. 11 healthy younger (18-40 years) and 10 older (65-89 years) phototype I-III volunteers received a single sub-erythemal dose of SSR (95% UVA, 5% UVB; 1.3 standard erythemal dose) during winter, to ~35% body surface area. Six 5mm buttock skin biopsies were taken: two from unexposed skin, two immediately post-UVR, and two at 24h post-UVR: from these 7DHC was quantified using the assay developed in aim 1. Blood was sampled at baseline, 24h and 7d post-UVR for vitamin D3. Skin baseline 7DHC concentration in younger adults was 0.22 ± 0.07 µg/mg and this did not significantly change post-UVR. Similarly the baseline level in older adults was 0.25 ± 0.08 µg/mg, with no significant change post-UVR. Serum vitamin D3 in younger adults was 1.5 ± 1.5 nmol/L, 3.1 ± 2.0 nmol/L and 2.0 ± 2.1 nmol/L at baseline, 24h and 7d post-UVR, and in older adults 1.5 ± 1.7 nmol/L, 2.5 ± 2.0 nmol/L and 1.7 ± 1.2 nmol/L, respectively. No significant between-group difference in 7DHC or vitamin D3 was seen. Thus, skin 7DHC concentration does not limit vitamin D3 synthesis in healthy older adults. Thirdly, the aim was to assess how a single UVR dose influences the production of 25(OH)D3, 24,25(OH)2D3 and the 24,25(OH)2D3:25(OH)D3 ratio, with comparison between young and older adults. The study involved the volunteers, UVR doses and blood sampling time-points described above. There was a significant increase in 25(OH)D3 from baseline (44.2 ± 22.9 nmoL/L) to 24h post-UVR (47.7 ± 22.3 nmoL/L) in the combined age-group (P=0.0445), with no differences found in 24,25(OH)2D3 in the combined group, or between young vs older volunteers. The 24,25(OH)2D3:25(OH)D3 ratio fell between baseline (0.088 ± 0.029) and 24h post-UVR (0.075 ± 0.021) in the combined group (P=0.0026). The data suggest that a low dose UVR challenge does not influence 24,25(OH)2D3 concentration, as has previously been described for an oral vitamin D source, or show any difference between young and older adults, with the significant difference seen in 24,25(OH)2D3:25(OH)D3 ratio between baseline and 24h post-UVR attributable to the increase in 25(OH)D3 concentration post-UVR. The final aim was to compare sun exposure behaviours and dietary vitamin D intake of young and older adults, and their impact on vitamin D status. The above 13 yo
Date of Award1 Aug 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorAnn Webb (Supervisor) & Lesley Rhodes (Supervisor)


  • analytical chemistry
  • dermatology
  • skin photobiology
  • vitamin D
  • 7-Dehydrocholesterol

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