Comprehensive Analysis of Seasonal and Geographical Variation in UVB Radiation Relevant for Vitamin D Production in Europe

Abstract

Dermal synthesis, following sun exposure, is the main source of vitamin D. This study characterizes ambient UVB radiation relevant for vitamin D production in Europe. A biological weighing function was applied to data from the Tropospheric Emissions Monitoring Internet Service (TEMIS) for 46 capital cities over an 18-year period (2004–2021) to isolate wavelengths relevant for vitamin D production (D-UVB). Cumulative and weighted D-UVB (CW-D-UVB) were calculated to approximate seasonal vitamin D accumulation and diminution. Monthly 25(OH)D concentration measurements were extracted from published reports. All data were analyzed by location and time. Despite a moderate latitudinal range (35–64° N), we observed large—up to five-fold—regional differences: the highest mean diurnal D-UVB dose of 5.57 kJ/m2 (SD = 3.55 kJ/m2) was observed in Nicosia (Cyprus) and the lowest in Reykjavik (Iceland, 1.16 ± 1.29 kJ/m2). Seasonal differences in diurnal D-UVB dose were even more pronounced, with a median 36-fold difference between annual peak and trough depending on a location (range: 10- to 525-fold). The mean duration of “vitamin D winter” was 126 days but varied widely (4 to 215 days). Monthly CW-D-UVB and 25(OH)D changes were very strongly correlated: the changes in 25(OH)D concentration increased by 12.6 nmol/L for every 100 kJ/m2 increment of CW-D-UVB in population-based studies (r2 = 0.79, p-value = 1.16 × 10−37). Understanding the differences in D-UVB radiation can help understand determinants of vitamin D status and guide region- and season-specific safe and effective sunlight exposure recommendations and vitamin D supplementation guidelines.

Influence of Strict Lockdown on Vitamin D Deficiency in Pregnant Women: A Word of Caution

“…The TEMIS project generates datasets of several key information items, and provides access to them free of charge via the internet (www.temis.nl/uvradiation/UVdose.html (accessed on 10 February 2023); version 2.0) [27]. D-UVB is the effective UV irradiance (expressed in kJ/m 2 ) reaching the Earth's surface integrated over the course of the day, and was calculated by considering the UVB radiation dose at the wavelengths that can induce cutaneous vitamin D production (290-315 nm) [7]. This database has been already used in the past and is described in detail elsewhere [28,29].…”

“…There was a decrease in the D-UVB dose by the end of the year, with the lowest point being reached in the second fortnight of December 2019, followed by a progressive increase in the D-UVB dose, reaching a peak by July 2020. "Vitamin D winter" has been defined as the threshold of D-UVB dose below which (<1 kJ/m 2 ) vitamin D synthesis is negligible [7,30]. In the area of our study, this would correspond to the period from December to mid-January (lasting <2 months).…”

“…Recently, it has been described that there are significant seasonal and regional differences in UVB radiation across Europe, which can have an impact on vitamin D production in the human body. Furthermore, monthly differences in cumulative and weighted UVB radiation, which take into account factors such as latitude, altitude, and cloud cover, are significantly correlated with changes in mean 25(OH)D levels in different populations [7].…”

“…This circumstance gave us the opportunity to describe how this enforced confinement influenced VDD prevalence. To adjust for 25(OH)D levels by sunlight irradiation in our study participants, we gathered the data of the vitamin D-specific UVB (D-UVB) dose received in the geographical area during the same period as the study [7].…”

More Than Bones: Aside Jobs of Vitamin D

“…Currently, it is well-accepted that vitamin D can be initially acquired from the diet (Hribar et al, 2022) or synthesized from cholesterol or ergosterol in the skin upon solar UV-B light exposure (Khanna et al, 2022). This vitamin D, or cholecalciferol or vitamin D 3 , is then transferred to the liver where it is converted to calcifediol or 25-hydroxycholecalciferol by hydroxylation of vitamin D 3 by the enzyme vitamin D 25-hydroxylase in the endoplasmic reticulum (Sulimovici et al, 1979).…”