Comparison of the Average Daily Vitamin D₃ Produced by Sunlight Exposure in Summer and the Winter: Across Sectional Study

Through exposure to the sun’s ultraviolet B (UVB) radiation, the skin produces more than ninety percent of the body’s vitamin D₃ needs. The primary objective of this study was to estimate and compare the mean concentration of vitamin D₃ (IU) produced by daily exposure to UV light during the summer and winter seasons. A cross-sectional study was conducted during the summer of 2022 and the winter of 2023, with male participants recruited exclusively. All participants resided in the Agadir region (30.428° N). A total of 324 men were included in the summer study and 345 in the winter study, with ages ranging from 18 to 100 years. Data were collected through a face-to-face interview questionnaire. The objective was to assess sun exposure variables in order to estimate the amount of vitamin D₃ produced by sunlight. The findings revealed that during the summer, vitamin D synthesis was below the recommended value of 600 IU/day in 0% of participants, between 600 and 1200 IU/day in 44.44% of participants, and ≥ 1200 IU/day in 55.55% of participants. During the winter period, 13.33% of participants exhibited a mean vitamin D synthesis below the recommended value of < 600 IU/day. In contrast, 74.20% exhibited a synthesis between 600 and 1200 IU/day, while 12.46% exhibited a synthesis of ≥ 1200 IU/day. For all groups of Moroccan men, daily vitamin D production by UV solar exposure appears to be sufficient to meet the daily vitamin D requirement in summer but not in winter. The primary predictors of mean daily vitamin D production by UV solar exposure are the fraction of the body exposed, age, and season.