Vitamin D status and sun exposure in the population of Saudi Arabia

Abstract

The primary vitamin D source is cutaneous production following solar ultraviolet radiation (UVR) exposure. Many factors affect this process, both external, related to the atmosphere/climate and internal, related to personal differences and human behaviour. However, this has not been explored in detail in the Saudi Arabian population. The first major aim of this thesis was to examine the climate of the studied region, relating to two cities, Makkah (Mecca) (21.42N), and Jeddah (21.29N). in particular the UVR, quantified by the ultraviolet index (UVI). Data were obtained from ground base measurement by a Biospherical instrument (GUV-2511) and compared with the satellite- derived sources and the radiative transfer model (LibRadtran). It was found that data from all three sources agreed on the same annual trend of a high recorded UVI in the summer reaching +10, and a UVI high enough to produce vitamin D in the winter reaching +6 whilst cooler temperatures enabled outdoor activities during the winter season. The second aim to quantify the dietary intake of the same participants in two seasons, using a one-week diet diary. 37% of the participants reported taking vitamin D supplements in the summer and 33% in the winter. Excluding the intake of supplements, the mean daily intake of vitamin D in the summer was 1.93 μg and 2.19 μg in the winter, which is lower than the recommended intake of 10 μg per day. A portion of the participants were taking very high levels of vitamin D supplements. the second aim was to conduct a two-centre longitudinal cohort study of 20-60 years old healthy Saudi Arabians examining: 25-hydroxyvitamin D (25(OH)D) levels, personal UVR exposure, time spent outdoors, and percentages of body surface exposed, alongside the dietary intake of vitamin D, and lifestyle factors related to sun exposure behaviours. 66 participants completed the study: (14 males and 52 females), the majority skin type IV. Questionnaires were used to recall lifestyle aspects such as: time spent outdoors, clothing, holiday, and sunscreen use. Participants recalled spending more time outdoors in the winter than the summer for the weekdays (p=0.007) and weekends (p=0.0001). This is expected after studying the region's climate, where very high temperatures were reported in summer and cool temperatures in winter. Serum 25(OH)D, the measurement of vitamin D status, showed no variation between summer and winter seasons, with 15%, 45%, and 40% of participants deficient, insufficient, and sufficient in the summer, and 25%, 35%, and 40% in the winter, respectively. Mean 25(OH)D was 45.6 nmol/L in summer and 47.9 nmol/L in winter. Median daily UVR weekday badge dose was higher in winter than summer (p= 0.019), while there was no significant difference in weekend doses. During weekdays, participants spent more time outside in summer and winter than on weekends (p=<0.0001 for both seasons). Overall, males spent more time outside during weekdays than females (summer p=0.0008; winter p=0.006). Most participants wore long sleeves and leg coverings most/all the time, males exposing a greater skin area on summer weekdays (p= <0.0001). The final aim of this thesis was to compare the Saudi population residing in Makkah- Jeddah (MJ) with that residing in Greater Manchester, United Kingdom (GM, 53.3N). 20 participants were recruited and completed the study in GM, where circulating 25(OH)D levels were only measured for the summer season. Participants completed a recall 12 questionnaire exploring lifestyle behaviour related to sun exposure habits. The MJ group had higher levels of 25(OH)D than those in GM (p= 0.0025). In comparison, GM participants recalled spending more hours outdoors during the summer weekdays than the MJ group (p=0.05), with no significant difference between the winter weekdays. The GM group recalled spending more hours outdoors on the summer weekend than the MJ group (p=0.04), with no significant difference between the two groups in the winter weekends. In conclusion, this study determined that 25(OH)D deficiency occurs in the Saudi population despite sufficient ambient UVR levels to produce vitamin D throughout the year. Intake of vitamin D was also low from natural food, with a lack of consumption of vitamin D fortified foods. Hence, it is important to enhance guidance for the Saudi population on vitamin D sources, including safe practices for sun exposure and recommended levels of supplementation to ensure safe dosage.