india too , is no exception . according to a projection from various studies on thyroid disease
, it has been estimated that about 42 million people in india suffer from thyroid diseases .
thyroid diseases are different from other diseases in terms of their ease of diagnosis , accessibility of medical treatment , and the relative visibility that even a small swelling of the thyroid offers to the treating physician .
this article will focus on five selected thyroid diseases ( hypothyroidism , hyperthyroidism , goiter / iodine deficiency disorders , hashimoto 's thyroiditis , and thyroid cancer ) and will offer an insight into studies on their prevalence . this review will also briefly cover the exciting work that is in progress to ascertain the normal reference range of thyroid hormones in india , especially in pregnancy and children . rather than being an exhaustive , in - depth review , this article will discuss selected studies from across the country and the implications and perspectives these studies bring forth , from an indian context .
among the various varieties of hypothyroidism , congenital hypothyroidism is probably the most important , as it is requires an early diagnosis , which is usually followed by appropriate therapy that can prevent the onset of brain damage .
studies from mumbai have suggested that congenital hypothyroidism is common in india , the disease occurring in 1 out of 2640 neonates , when compared with the worldwide average value of 1 in 3800 subjects .
this delay is attributable to the lack of awareness about the illness , as well as the lack of facilities available or screening program in place to comprehensively screen and test newborns for this illness . in childhood too , hypothyroidism can occur . in a clinic - based study from mumbai , out of 800 children with thyroid disease ,
common causes of hypothyroidism in these children were thyroid dysgenesis , dyshormonogenesis , and thyroiditis . among adult people in india , the prevalence of hypothyroidism has been recently studied . in this population - based study done in cochin on 971 adult subjects ,
the prevalence of subclinical hypothyroidism was also high in this study , the value being 9.4% . in women ,
the prevalence was higher , at 11.4% , when compared with men , in whom the prevalence was 6.2% .
the prevalence of subclinical hypothyroidism increased with age . about 53% of subjects with subclinical hypothyroidism were positive for anti - tpo antibodies .
this was a population - based study , which used cluster sampling strategy . in this study
, urinary iodine status was studied in 954 subjects from the same population sampled , and the median value was 211 g / l ; this suggested that this population was iodine sufficient .
the prevalence of hyperthyroidism has been studied in several studies . in an epidemiological study from cochin ,
subclinical and overt hyperthyroidism were present in 1.6% and 1.3% of subjects participating in a community survey . in a hospital - based study of women from pondicherry ,
more than a third of community - detected hyperthyroid cases have positive anti - tpo antibodies , and about 39% of these subjects have a goiter [ figure 1 ] .
prevalence of thyroid function abnormalities found in 971 adult subjects form a community study from kerala , south india .
autoimmune thyroid disease is probably commoner than iodine deficiency as a cause of goiter in areas that are now iodine sufficient .
however , given that iodine deficiency is a problem in india , the importance of iodine deficiency can not be underestimated in the indian context .
the link between endemic goiter and iodine deficiency has been researched in india by several eminent researchers , and this has led to the publication of several important reports.[57 ] critical research has resulted in endemic goiter being reported from all over the country and not just from the himalayan and sub - himalayan regions .
researchers from new delhi had shown that this was linked to iodine deficiency and that this resulted in decompensated hypothyroidism in many cases .
this led to landmark studies which showed that iodine deficiency was associated with hypothyroidism in neonates , setting the scene for the now legendary salt iodization program supported by the government of india .
subsequent to this program , it was shown that in selected regions of uttar pradesh , the prevalence of congenital hypothyroidism had come down from 100/1000 to 18/1000 .
several landmark studies have been carried out in the area of iodine deficiency disorders in the country.[57 ] in the postiodization phase , what happens to the prevalence of goiter ?
about 14,762 children from all over india were studied for the following characteristics : goiter prevalence , urinary iodine and thiocyanate excretion , functional status of the thyroid , as well as serological and cytopathological markers for thyroid autoimmunity .
about 23% of subjects had a goiter . a significantly higher level of median urinary thiocyanate ( uscn ) excretion was noted in goitrous subjects ( 0.75 mg / dl ) when compared with controls ( 0.64 mg / dl ; p < 0.001 ) .
the authors suggested that despite iodization , the prevalence of goiter has not dramatically declined .
the researchers noted that thyroid autoimmunity could only partly explain the goiter and concluded that the role of goitrogens is an area that deserves further study .
population studies have suggested that about 16.7% of adult subjects have anti - thyroid peroxidase ( tpo ) antibodies and about 12.1% have anti - thyroglobulin ( tg ) antibodies . in this same study of 971 subjects ,
when subjects with abnormal thyroid function were excluded , the prevalence of anti - tpo and anti - tg antibodies was 9.5% and 8.5% . in a landmark study of hashimoto 's thyroiditis in india ,
6283 schoolgirls from all over the country were screened . among them , 1810 schoolgirls had a goiter . among them 764 subjects underwent a fine needle aspiration cytology , and of these subjects , 58 ( 7.5% ) had evidence of juvenile autoimmune thyroiditis ( the term included both hashimoto 's thyroiditis and focal lymphocytic thyroiditis ) . among fine needle aspiration
cytology - confirmed cases of juvenile autoimmune thyroiditis , subclinical and overt hypothyroidism were seen in 15% and 6.5% , respectively .
the indian council of medical research established the national cancer registry program , and the ncrp has collected the data of more than 3,00,000 cancer patients between the periods 1984 and 1993 . among these patients ,
the ncrp noted 5614 cases of thyroid cancer , and this included 3617 females and 2007 males .
the six centers involved in the studies were at mumbai , delhi , thiruvananthapuram , dibrugarh , chandigarh , and chennai . among them , thiruvananthapuram had the highest relative frequency of cases of thyroid cancer among all cancer cases enrolled in the hospital registry , 1.99% among males and 5.71% among females .
the age - adjusted incidence rates of thyroid cancer per 100,000 are about 1 for males and 1.8 for females as per the mumbai cancer registry , which covered a population of 9.81 million subjects .
the histological types of thyroid cancer were studied in a hospital cancer registry of 1185  new cases  of thyroid cancer .
the commonest cancer type was papillary , followed by follicular cancer , and the results are summarized in figure 2 .
anaplastic , cancer not - otherwise specified and no histology proof - cases , together , accounted for 223 cases in this survey
in the past 2 years , exciting work has been carried out to understand the thyroid in pregnancy and childhood in india.[1214 ] in the first article , marwaha et al indicate the normal reference ranges of ft4 , ft3 , and tsh in pregnant women , and used the 5 and 85 percentile to define the reference ranges in the disease - free subjects .
the authors report that the trimester - wise values in the first , second , and third trimesters were ft(3 ) ( 1.925.86 , 3.25.73 , and 3.35.18 pm / l ) , ft(4 ) ( 1219.45 , 9.4819.58 , and 11.3217.7 pm / l ) , and tsh ( 0.65.0 , 0.445.78 , and 0.745.7 iu / ml ) , respectively . with regard to iodine deficiency during pregnancy ,
a hospital - based study from kolkata has suggested that pregnant women from their center were iodine sufficient . in a large epidemiological study of 24,685 students from all over india published in 2010 ,
the authors attempted to define normative data on thyroid hormone levels in healthy school children . among them
, the authors calculated the reference ranges from the 5343 subjects . in a separate publication in 2008 , the same authors studied normative thyroid hormone ranges in 5122 school children , after excluding children who had a personal or family history of thyroid disease , used thyroid medications , had a goiter , and had hypoechogenicity / nodularity on ultrasound or positivity for serum anti - tpo antibodies .
the authors reported that for tsh , the 97th percentile was in the range 6.018.4 miu / l for boys and 5.288.04 miu / l for girls .
this , as the authors themselves suggest , offers a compelling argument against lowering the reference range of tsh in this population .
interesting work is in progress to ascertain the predictors of thyroid gland size in an indian population . in a study of 1002 children from gujarat ,
the authors note that the prevalence of goiter was very high ( 80% ) when assessed by ultrasound .
this was also a population with a high prevalence of malnutrition ( 82% subjects were underweight ) . in this population , the authors note that thyroid size was related to several anthropometric parameters .
however , it is not clear whether these results are applicable to the general indian population . in the state of gujarat , the same group had reported that iodine deficiency continues to be a problem , as more than 20% of the population had a very low median urinary iodine of < 50 g / l . in the same population , the prevalence of hypothyroidism has been reported to be about 7% .
the use of ultrasound in population studies of thyroid gland size is an exciting new area for research in the field of thyroid epidemiology.[1820 ]
 thyroid diseases are common worldwide . in india too , there is a significant burden of thyroid diseases . according to a projection from various studies on thyroid disease 
 , it has been estimated that about 42 million people in india suffer from thyroid diseases . 
 this review will focus on the epidemiology of five common thyroid diseases in india : ( 1 ) hypothyroidism , ( 2 ) hyperthyroidism , ( 3 ) goiter and iodine deficiency disorders , ( 4 ) hashimoto 's thyroiditis , and ( 5 ) thyroid cancer . 
 this review will also briefly cover the exciting work that is in progress to ascertain the normal reference range of thyroid hormones in india , especially in pregnancy and children . 
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