Vol.:(0123456789) 1 3 Photochemical & Photobiological Sciences https://doi.org/10.1007/s43630-021-00115-w ORIGINAL PAPERS Low vitamin D in dark‑skinned immigrants is mainly due to clothing habits and low UVR exposure: a Danish observational study Pameli Datta 1  · Peter Alshede Philipsen 1  · Luise Winkel Idorn 1  · Hans Christian Wulf 1 Received: 1 May 2021 / Accepted: 11 October 2021 © The Author(s), under exclusive licence to European Photochemistry Association, European Society for Photobiology 2021 Abstract Low 25-hydroxyvitamin D 3 (25(OH)D) among dark-pigmented persons has been observed. To elucidate the reason for this we examined sun behaviour, sun-exposed body area, solar UVR exposure and 25(OH)D levels in immigrants with dark pigmented skin and Danes with light pigmented skin. Clothing, sun behaviour, and diet were recorded daily during a Danish summer season (93 analysed days). Erythema-weighted UVR doses were measured by personal electronic UVR dosimeters (with erythema response, measurement every 5th second) and 25(OH)D was measured in 72 participants (33 dark-skinned and 39 light-skinned). The immigrants exposed 28% less skin area, received 70% less UVR dose, and had 71% less 25(OH) D increase during the summer. The UVR reactivity (Δ25(OH)D per joule accumulated UVR dose) was similar (P = 0.62) among the immigrants (0.53 nmol l −1  J −1 ) and the Danes (0.63 nmol l −1  J −1 ). In the groups combined, 25(OH)D levels after summer were mainly infuenced by UVR dose to exposed skin (28.8%) and 25(OH)D start level (27.9%). Height and measured constitutive skin pigmentation were of minor infuence: 3.5% and 3.2%, respectively. Sun exposure and clothing habits were the main reasons for lower 25(OH)D level after summer in the darker immigrants, as both groups had similar UVR reactivity. Graphical abstract 0 50 100 150 All days Work- days Days off work Days with body exposure UVR (SED) UVR, sun exposed BSA, 25(OH)D 3 increase and UVR reactivity UVR reactivity nmol l -1 J -1 10 20 30 40 25(OH)D increase nmol l -1 Sun exposed BSA m 2 0 0 0 1.0 0.8 0.6 0.4 0.2 1.0 0.5 Immigrants Danes - - 1 Introduction When human skin is exposed to UVR from terrestrial sun- light, cutaneous 7-dehydrocholesterol (7-DHC) is converted into previtamin D 3 ultimately leading to the formation of the bioactive vitamin D, 1,25(OH)2D3 [1]. Melanin (pigment) in skin absorbs UVR [2–4] and can ofer more than 20-fold protection against skin cancer [5–7]. The melanin protection factor is 8–10 for erythema and around 60 for DNA photo- damage in the basal layer of the skin [6]. Individuals with relatively darkly pigmented skin display insufcient (< 50 nmol l −1 ) serum 25-hydroxyvitamin D 3 (25(OH)D) levels much more frequently than individuals with more lightly pigmented skin. This is particularly com- mon when persons with dark skin immigrate to higher lati- tudes with less ambient UVB, but is generally present irre- spective of their place of residence [8]. This phenomenon is * Pameli Datta pameli@outlook.dk 1 Department of Dermatology D92, Bispebjerg Hospital, University of Copenhagen, Nielsine Nielsens Vej 17, 2400 Copenhagen NV, Denmark