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Vitamin D in blood is higher in winter than summer – in Middle-East Sept 2011

A Counterintuitive Seasonal Effect in Vitamin D Levels in Adult, Overweight and Obese Middle-eastern Residents

Al-Daghri NM, Al-Attas OS, Alokail MS, Alkharfy KM, El-Kholie E, Yousef M, Al-Othman A, Al-Saleh Y, Sabico S, Kumar S, Chrousos GP.
Biomarkers Research Program, Biochemistry Department, College of Science, King Saud University, Riyadh 11451, Kingdom of Saudi Arabia (KSA)
Center of Excellence in Biotechnology Research Center, King Saud University, Riyadh 11451, Saudi Arabaia
Prince Mutaib Chair for Biomarkers of Osteoporosis, King Saud University, Riyadh 11451, KSA
Clinical Pharmacy Department, College of Pharmacy, King Saud University, Riyadh 11451, KSA
Health Affairs for Riyadh Region, Ministry of Health, Riyadh 11175, KSA
College of Applied Medical Sciences, King Saud University, Riyadh 11451, KSA
King Abdulaziz Medical City, Riyadh 11426, KSA
Clinical Sciences Research Institute, Diabetes and Metabolism Unit, Coventry CV47AL, UK
First Department of Pediatrics, Athens University Medical School, Athens 11527, Greece.
75 Issue 4, Clinical Endocrinology
PMID: 21906116

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 in order 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:? 121 adult, overweight and obese, consenting Saudis aged 18-70 years were randomly recruited from 4 Primary Health Care Centers (PHCCs) 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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See also VitaminDWiki