Al-Daghri, Nasser M., Al-Attas, Omar S., Alokail, Majed S., Alkharfy, Khalid M., El-Kholie, Emad, Yousef, Mansour, Al-Othman, Abdulaziz, Al-Saleh, Yousef, Sabico, Shaun, Kumar, Sudhesh and Chrousos, George P.. (2012) Increased vitamin D supplementation recommended during summer season in the gulf region : a counterintuitive seasonal effect in vitamin D levels in adult, overweight and obese Middle Eastern residents. Clinical Endocrinology, Vol.76 (No.3). pp. 346-350. ISSN 0300-0664

Abstract

Purpose  Seasonal variations in circulating vitamin D levels provide vital information as to the most appropriate time to either start or increase vitamin D supplementation to maintain optimal vitamin D levels. In this follow-up study, we determined seasonal differences in serum 25(OH)-vitamin D (25(OH)D) levels, as well as parallel changes in metabolic parameters, in a cohort of adult, overweight and obese Saudis. Methods  A total of 121 adult, overweight, obese, and consenting Saudis aged 18–70 years were randomly recruited from four Primary Health Care Centers in Riyadh, Saudi Arabia. They were divided according to the season when baseline measurements were made [74 summer (April–October); 47 winter (November–March)]. Anthropometrics were obtained, and fasting blood samples were taken at baseline and every 3 months for 1 year. Fasting blood glucose, corrected calcium levels, and lipid profiles were measured routinely. Serum 25(OH)-vitamin D was quantified using a specific enzyme-linked immunosorbent assay (ELISA). Results  Age- and BMI-matched mean 25(OH)-vitamin D levels from the winter group were significantly higher than those of the summer group (P < 0·001). In both groups, HDL-C levels improved significantly as 25(OH)-vitamin D levels increased with subsequent follow-ups, even after adjusting for age, gender and BMI (P < 0·001). Conclusion  Seasonal differences in serum 25(OH)-vitamin D levels in Saudi Arabia are counterintuitive, with circulating levels being higher during the winter than the summer season. Increased vitamin D supplementation is thus recommended to maintain optimal serum 25(OH)-vitamin D levels during the summer season.

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