Background and Objectives: The National Food and Nutrition Surveillance (FNS), with the aim of providing information for policy makers, was established in Iran since 2014. For the first couple of years, it focused on the problem of vitamin D deficiency. The scope of this paper is to translate information about the vitamin D status to policy. Materials and Methods: In total, 667 apparently healthy children aged 5-18 years were randomly selected from six regions of Iran (West Azerbaijan, Semnan, Lorestan , South Khorasan, Khozestan, and Fars). Blood samples were obtained after an overnight fasting in two seasons (winter and summer). Results: About 93% and 72% of the children had undesirable vitamin D status (25(OH)D<50 nmol/L) in winter and summer, respectively. In all provinces, the mean serum 25(OH)D increased in summer significantly, with the highest rise in West Azerbaijan. Conclusions: Repeatedly reported high prevalence of hypovitaminosis D has made the policy makers to urgently implement a high-dose supplementation program (50’000 IU/mo) in schools. By this means, it can be expected that calcidiol concentrations increase about 42 to 50 nmol/L, and then during summer, the prevalence of deficiency would return to the baseline (~72%). Based on our findings, in summer, the highest concentrations of 25(OH)D will reach to the range of 85-103 nmol/L that even with 2SD, the peak concentration will still be far from toxic levels. Continuation of vitamin D supplementation for children during summer is, therefore, recommended. Keywords: Vitamin D Deficiency, Children, Seasonal change, Supplementation