it seems that complications of vitamin d deficiency have been completely removed by having enriched food by vitamin d , but rachitism is the top of iceberg of vitamin d deficiency .
vitamin d deficiency can also causes osteopenia , osteoporosis , and muscle weakness and increases risk of hip fracture in adults .
the most important effect of vitamin d is on parathyroid and bone and also plays a key role on the calcium absorption from the gut .
the discovery of vitamin d receptor in most tissues and organs has developed a new perception from effects of vitamin d. for instance , vitamin d can decrease risk of many chronic diseases , cancers , autoimmune disease , infectious , and cardiovascular disease .
it has been estimated that one billion people are vitamin d deficient in the world .
this deficiency is common in all different cities with the same level of the sea or cities with lower geographic latitude .
20 ng / ml is the level of vitamin d deficiency and 20 < 25 ( oh ) d < 30 ng / ml is recognized as a vitamin d insufficiency . there are different ways to detect cut - off points for vitamin d deficiency .
for instance , based on inverse relation between 25 ( oh ) d and pth , a direct relation between 25 ( oh ) d and 1 , 25 ( oh ) d and effect of vitamin d on fracture risk .
the level of 25 ( oh ) d that would be enough for pth suppression , probably , is a suitable criterion for bone health and cut - off point for vitamin d deficiency .
the aim of this study was detection of prevalence of vitamin d deficiency in secondary students in arak , a centrally located city in iran , and also detection of cut - off points for vitamin d deficiency .
in a cross - sectional study in november 2010 , 420 students including 220 girls and 200 boys from secondary students from 10 to 16 years old were selected by a multistage sampling .
first , all of the secondary schools were divided into two areas and then 21 schools including 11 girls schools and 10 boys , schools were selected by a cluster sampling .
finally , the samples were picked up by a systematic random procedure based on the student 's initials .
all the students and their parents were informed about the study and signed off the consent form .
inclusion criteria were lack of hepatic , renal , bone disease and cancer , no history of intake of anticonvulsant drugs , calcium , vitamin d , and antineoplastic drugs .
laboratory tests including hepatic , renal , calcium , phosphoros , alp ( alkaline phosphatase ) , albumin , pth , 25 ( oh ) d. 25 ( oh ) d levels by ria and pth by irma were measured ( made by bio source europe sa , belgium ) and its intensity categorized into three levels . 

mild deficiency : 15  25 ( oh ) d < 20 ng / ml.moderate deficiency : 8  25 ( oh ) < 15 ng / ml.severe deficiency : 25 ( oh ) < 8 ng / ml . 
  mild deficiency : 15  25 ( oh ) d < 20 ng / ml . moderate deficiency : 8  25 ( oh ) < 15 ng / ml . severe deficiency : 25 ( oh ) <
8 ng / ml . the relation between vitamin d and pth was assessed by the scatter chart . the level of vitamin d that pth was increasing , defined as cut - off points for vitamin d deficiency .
the prevalence of vitamin d deficiency in different intensities was assessed by spss 15 and variables compared between girls and boys , and also between deficient and sufficient vitamin d groups by student 's test or mann -- whitney u based on normal distribution based on k -- s ( kolmogrov -- smirnov ) test .
the pearson test was used to identify the relation between 25 ( oh ) d and age , weight , and bmi .
a total of 420 students including 46.9% boys and 53.1% girls participated in this study . mean age for boys and girls was 12.5  1 and 12.7  1 years old respectively p = 0.1 [ table 1 ] . mean characteristic of students ( mean  sd ) mean age of vitamin d - deficient and nondeficient groups based on cut - off 25 ( oh ) d
< 20 ng / ml were 12.6  1 and 12.6  2 years old respectively ( p = 0.5 ) . but mean bmi in two groups were 20  3.5 and 19  2.1 respectively ( p = 0.02 ) .
there was no meaningful relation between 25 ( oh ) d and age ( p = 0.5 ) but there was an inverse relation between 25 ( oh ) d level and bmi ( r = -0.17 ) ( p = 0.01 ) , weight ( r = -0.14 ) ( p = 0.05 ) , pth ( r = -0.262 ) ( p = 0.001 ) .
there was also a meaningful relation between vitamin d deficiency and sex ( p = 0.001 ) .
based on the logistic regression analysis , the girls have 54.4 times more chance than boys for vitamin d deficiency ( or 54.4 ) ( p < 0.001 ) . totally 84% of the students had vitamin d deficiency [ table 2 ] .
three cut - off points 33 , 21 , and 13 ng / ml were defined for mild , moderate , and severe vitamin d deficiency [ figure 1 ] using the scatter chart .
the prevalence of vitamin d deficiency based on different intensities was evaluated in both genders [ table 3 ] .
prevalence of vitamin d deficiency in students ( number/% ) mean of pth of different cut - off points for vitamin d deficiency prevalence of vitamin d deficiency based on local cut - off points ( % )
our findings in arak , a centrally located city of iran , showed a high prevalence of vitamin d deficiency of 84% among the students .
the results showed that females were more likely to be vitamin d - deficient than males .
the present study suggests three local cut - off points for vitamin d deficiency based on 25 ( oh ) d < 13 , 21 , and 33 ng / ml . vitamin d deficiency is a common medical problem throughout the world .
it has been predicted that one billion people throughout the world are vitamin d deficient .
prevalence of vitamin d deficiency in the countries where food is enriched by vitamin d ( scandinavian countries ) is 1.614.8% . in other european countries , among middle - aged and elderly people , 14 - -59.6 in tunessia 47.6% and finally among teenagers in boston was 24.1% .
a total of 30 - -50% of people in india , lebanon , and turkey and also 45.2% of females in china were vitamin d deficient .
several studies in different parts of iran and among different age groups have shown a high prevalence of vitamin d deficiency.[1114 ] prevalence of vitamin d deficiency in tehran ( the capital city of iran ) was 60% in males and 91% in females .
the prevalence of vitamin d deficiency in isfahan , another central city of iran , was 46.2% among students including 72.1% girls and 18.3% boys and is similar to our findings in tabriz , another city in the north west of iran , which was 64.2% among females ( mild 33.7% , moderate 15.5% , severe 15.1% ) that in comparison with the present study is lower .
another study in different cities of iran , with different climate , showed that 27.2% of females and 37.25% of males had a mild vitamin d deficiency , and also 47.85% of females and 34.75% of males had moderate to severe vitamin d deficiency that confirms the present study .
different etiologies , such as insufficient sun exposure , clothing habits , and insufficient intake of vitamin d , may explain high prevalence of vitamin d deficiency .
it has been shown that 2-years intake of calcium and vitamin d , increased serum 25 ( oh ) d level up to 28% .
serum 25 ( oh ) d levels were lowest in blacks and highest in white people .
although some studies found that sun expose and clothing habits were not different between sufficient and deficient groups .
decreased calcium intake lead to increased serum pth level and increased catabolism of 25 ( oh ) d. awumey et al
. showed higher activity of 24-hydroxylase in fibroblasts that lead to increased catabolism of 25 ( oh ) d of indian americans .
the darker skin of the asian immigrants to european countries is another risk for vitamin d deficiency .
found that 61% of the turkish group ( in turkey ) and 55% of the turkish immigrant group in germany had bone and muscle pain , while it was 15% within the german group with higher serum 25 ( oh ) d levels .
our findings showed that the prevalence of vitamin d deficiency is much more in girls than boys ( girls 99.1% , 66.5% boys ) ( p < 0.001 ) .
another study in iran , isfahan , also found that the prevalence of vitamin d deficiency was four times more in girls than boys and severe vitamin d deficiency in girls and boys were 14.5% and 0.6% respectively .
another study in iran also found that moderate - to - severe vitamin d deficiency was much more in females than males .
differences according to gender and age group maybe because of biological differences but might also due to behavioral differences
. there might be gender - specific clothing differences ( necessarily not based on a culture religious ) .
there also might be that females spend less time outside , resulting in less exposure to the sun .
another study in the united states among female soldiers found that vitamin d levels decrease during military training in the summer due to the type of clothing worn during training , coupled with inadequate vitamin d intake .
our study found that vitamin d deficiency was not associated with the age , while most studies found higher prevalence of vitamin d deficiency among elderly , probably due to lower capacity of the skin to produce vitamin d after sun exposure or less vitamin d intake in elderly , although a few studies reported higher prevalence of vitamin d deficiency in young people .
our study shows a significant inverse association between bmi ( body mass index ) and weight in one hand with vitamin d deficiency in another hand , same as the tabriz study and against the isfahan study .
considering the role of fat tissue as a depot of vitamin d , obese have increased storage capacity of 25 ( oh ) d , that leads to lower serum vitamin d levels .
we determined three cut - off points for vitamin d deficiency based on 25 ( oh ) d < 33 , 21 , and 13 ng / ml for mild , moderate , and severe vitamin d deficiency , using scatter chart , versus 12.5 , 25 , and 40 ng / ml in another study in iran and 32 ng / ml in isfahan .
high prevalence of vitamin d deficiency probably could be the result of above - mentioned combination .
we recommend that some efforts could be made to encourage people to intake vitamin d and calcium supplements and also have more exposure to the sunlight .
 introduction : vitamin d has a basic role in bone growth and metabolism and has been noticed for its important role in many diseases , such as diabetes , depression , hypertension , and cardiovascular disease . regarding some studies , 
 detection of vitamin d deficiency in different places has important implication for health . 
 this study determined prevalence of vitamin d deficiency in arak , a centrally located city in iran.materials and methods : based upon a cross - sectional study in 2010 , 420 students 10 - -16 years old including 220 girls and 200 boys , studied at arak secondary schools , were selected by a multistage sampling . 
 the level of 25 ( oh ) d and pth ( parathormone ) was measured and also the prevalence of vitamin d deficiency in different intensities was evaluated and compared between girls and boys by the student t - test . 
 vitamin d deficiency for the students was categorized into three intensities based on three levels of 25 ( oh ) d : mild deficiency - 15  25 ( oh ) d < 20 ng / ml , moderate deficiency -- 8  25 ( oh ) < 15 ng / ml , severe deficiency - 25 ( oh ) < 8 ng / ml . the relationship between the 25 ( oh ) d and pth was assessed by scatter chart to define cut - off points for vitamin d deficiency.results:based on 25 ( oh ) d < 20 ng / ml , 84% of the students had vitamin d deficiency including 60.7% mild , 22.4% moderate , and 0.7% severe . 
 three local cut - off points including 13 , 21 , and 33 ng / ml were defined in the scatter chart . 
 the results showed that the deficiency of vitamin d in girls is much more than that in boys ( p = 0.05).conclusion : the high prevalence of vitamin d deficiency could be probably a result of different etiologies . 
 we recommended that people should be encouraged to take vitamin d and calcium supplements and also they should have more exposure to the sunlight . 
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