International Journal of Preventive Medicine (Int J Prev Med)2008-78023520110712233233ENIsfahan Eye Research Center (IERC), Department of Neurology, Medical School, Isfahan University of Medical Sciences, Isfahan, IranIsfahan Eye Research Center (IERC), Ophthalmology Ward, Feiz Hospital, Isfahan University of Medical Sciences, Isfahan, IranIsfahan Eye Research Center (IERC), Ophthalmology Ward, Feiz Hospital, Isfahan University of Medical Sciences, Isfahan, IranIsfahan Eye Research Center (IERC), Ophthalmology Ward, Feiz Hospital, Isfahan University of Medical Sciences, Isfahan, IranIsfahan Eye Research Center (IERC), Ophthalmology Ward, Feiz Hospital, Isfahan University of Medical Sciences, Isfahan, IranIsfahan Eye Research Center (IERC), Department of Neurology, Medical School, Isfahan University of Medical Sciences, Isfahan, IranIsfahan Eye Research Center (IERC), Neuroimmunology Unit, Center for Neuroscience and Trauma, Blizard Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London, UKIsfahan Eye Research Center (IERC), Isfahan University of Medical Sciences, Isfahan, Iran201106272011070820110706<p><strong>Objectives: </strong>The onset of multiple sclerosis in the majority of the cases occurs as a clinically isolated syndrome (CIS). We sought to assess serum levels of 25-hydroxyvitamin D (25-OHD) in CIS patients and healthy controls.</p> <p><strong>Methods: </strong>In this cross-sectional study 40 patients (36 women and 4 men) with CIS manifesting as a single isolated optic neuritis and 40 Age- and sex-matched healthy controls (35 women and 5 men) were enrolled between late October 2010 and early March 2011. General vitamin D deficiency was defined as serum 25-OHD levels of lower than 20 ng/ml and was classified as mild (15 &lt; 25-OHD &lt;20 ng/ml), moderate (8 &lt; 25-OHD &lt;15 ng/ml), and severe (25- OHD &lt;8 ng/ml).</p> <p><strong>Results: </strong>We found no difference in the median interquartile range [IQR] between CIS patients and controls (17.95 [10.40- 29.13] vs. 17.00 [12.25-31.00]; <em>P</em>=0.57). However, when stratified by the levels of deficiency, among CIS patients a significantly higher proportion had severe vitamin D deficiency in comparison to healthy controls (20% vs. 2.5%; <em>P</em>=0.034). Nevertheless, the frequency of general (62.5% vs. 60%, <em>P</em>=0.82), mild (25% vs. 30%, <em>P</em>=0.80), and moderate (17.5% vs. 27.5%, <em>P</em>=0.42) vitamin D deficiency were not different between the two groups.</p> <p><strong>Conclusions: </strong>Our findings do not indicate any significant difference of serum 25-OHD between CIS patients and healthy controls. However, in our series severe vitamin D deficiency was more frequent among CIS patients.</p> <strong>Keywords: </strong>25-Hydroxyvitamin D, Vitamin D deficiency, optic neuritis, multiple sclerosis, risk factor, prevention, Isfahan, Iranhttp://ijpm.mui.ac.ir/index.php/ijpm/article/view/233http://ijpm.mui.ac.ir/index.php/ijpm/article/download/233/518