Effect of latitude on seasonal variations of vitamin d and some cardiometabolic risk factors: National food and nutrition surveillance

Abstract

Background: Despite a remarkable reduction in the occurrence of many micronutrient deficiencies in most countries, vitamin D deficiency has remained a global problem. Age-adjusted disability-adjusted life years lost due to cardiovascular disease in the Eastern Mediterranean Region, including in the Islamic Republic of Iran, are higher than the global average. Aims: To assess the effects of latitude and season on vitamin D status in the Iranian population and the association be­tween vitamin D status and certain cardiometabolic risk factors. Methods: A sample of 1111 participants aged 19-65 years was randomly selected from 6 regions with latitudes ranging from 29º.0 N to 37.5º N. All anthropometric and biochemical assessments were performed twice a year, summer and winter during 2013 to 2014. Results: Overall mean 25(OH)D concentration was 26.9 [standard deviation (SD) 17.8] nmol/L in winter and 43.4 (SD 32.9 nmol/L in summer (P < 0.001). Poor vitamin D status was noticeable in both seasons (90.1% and 69.2%, respectively). Be­ing male (B, 7.6; 95% CI: 4.3 to 10.8; P < 0.001) and living at a latitude higher than 33 ° were positive predictors, and serum 25(OH)D concentration in winter (B, -0.2; 95% CI: -2.9 to -0.11; P < 0.001) was a negative predictor of changes of 25(OH)D concentrations. Conclusion: We found a high prevalence of suboptimal vitamin D status in Iranian adults throughout the year, irrespec­tive of latitude and season. Improvement of mean circulating 25(OH)D concentrations in the community to 50+ nmol/L through a fortification programme is likely to engender healthy cardiometabolic changes.