Thyroid disorders in India: An epidemiological perspective

Abstract

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.

Full text

Indian Journal of Endocrinology and Metabolism / 2011 / Vol 15 / Supplement 2
S78
Thyroid disorders in India: An epidemiological
perspective
Ambika Gopalakrishnan Unnikrishnan, Usha V. Menon
Department of Endocrinology, Amrita Institute of Medical Sciences, Cochin, Kerala, India
ABSTRACT
Thyroid diseases are common worldwide. In India too, there is a signicant 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 ve common thyroid diseases in India: (1) hypothyroidism, (2) hyperthyroidism, (3) goiter and iodine
deciency disorders, (4) Hashimoto’s thyroiditis, and (5) thyroid cancer. This review will also briey cover the exciting work that is in
progress to ascertain the normal reference range of thyroid hormones in India, especially in pregnancy and children.
Key words: Hypothyroidism, India, thyroid
Review Article
Corresponding Author: Dr. A. G. Unnikrishnan, Department of Endocrinology, Amrita Institute of Medical Sciences, Cochin, Kerala, India.
E-mail: unnikrishnanag@gmail.com
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DOI:
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IntRoductIon
Thyroid diseases are, arguably, among the commonest
endocrine disorders worldwide. 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.[1] 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. Early diagnosis and treatment remain
the cornerstone of management.
This article will focus on ve selected thyroid diseases
(hypothyroidism, hyperthyroidism, goiter/iodine deciency
disorders, Hashimoto’s thyroiditis, and thyroid cancer) and
will offer an insight into studies on their prevalence. This
review will also briey 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.
HypotHyRoIdIsm
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.[2] There is
often a delay in the diagnosis of congenital hypothyroidism
in the country. 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, 79% had hypothyroidism. Common causes of
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Indian Journal of Endocrinology and Metabolism / 2011 / Vol 15 / Supplement 2 S79
hypothyroidism in these children were thyroid dysgenesis,
dyshormonogenesis, and thyroiditis.[2]
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 hypothyroidism was 3.9%.[3] 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.[3] In this study, Urinary Iodine
Status was studied in 954 subjects from the same population
sampled, and the median value was 211 µg/l; this suggested
that this population was iodine sufcient.
HypeRtHyRoIdIsm
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.[3] In a hospital-based study of women from
Pondicherry, subclinical and overt hyperthyroidism were
present in 0.6% and 1.2% of subjects.[4] More than a third
of community-detected hyperthyroid cases have positive
anti-TPO antibodies, and about 39% of these subjects have
a goiter[3] [Figure 1].
GoIteR and IodIne defIcIency
Recent population studies have shown that about 12% of
adults have a palpable goiter.[3] Autoimmune thyroid disease
is probably commoner than iodine deciency as a cause
of goiter in areas that are now iodine sufcient. However,
given that iodine deciency is a problem in India, the
importance of iodine deciency cannot be underestimated
in the Indian context.
The link between endemic goiter and iodine deciency has
been researched in India by several eminent researchers,
and this has led to the publication of several important
reports.[5-7] Critical research has resulted in endemic goiter
being reported from all over the country and not just from
the Himalayan and Sub-Himalayan regions.[1] Researchers
from New Delhi had shown that this was linked to
iodine deciency and that this resulted in decompensated
hypothyroidism in many cases.[1] This led to landmark
studies which showed that iodine deciency was associated
with hypothyroidism in neonates, setting the scene for the
now legendary salt iodization program supported by the
Government of India.[1] 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.[1] Several landmark studies have
been carried out in the area of iodine deciency disorders
in the country.[5-7]
In the postiodization phase, what happens to the prevalence
of goiter? This very important question was answered in
an elegantly conducted study.[8] 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 signicantly 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.[8] 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.
autoImmune tHyRoIdItIs In IndIa
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%.[3]
In a landmark study of Hashimoto’s thyroiditis in
India, 6283 schoolgirls from all over the country were
Unnikrishnan and Menon: Thyroid disorders in India
Figure 1: Prevalence of thyroid function abnormalities found in 971 adult
subjects form a community study from Kerala, South India.[3]
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Indian Journal of Endocrinology and Metabolism / 2011 / Vol 15 / Supplement 2
S80
screened.[9] Among them, 1810 schoolgirls had a goiter.
Among them 764 subjects underwent a ne 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 ne needle aspiration cytology-conrmed cases
of juvenile autoimmune thyroiditis, subclinical and overt
hypothyroidism were seen in 15% and 6.5%, respectively.[9]
tHyRoId canceR and IndIa
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.[10] 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 nationwide
relative frequency of thyroid cancer among all the cancer
cases was 0.1%–0.2%. 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.[11] The
commonest cancer type was papillary, followed by follicular
cancer, and the results are summarized in Figure 2.
RefeRence RanGes of tHyRoId functIon
In pReGnancy and cHIldRen
In the past 2 years, exciting work has been carried out
to understand the thyroid in pregnancy and childhood
in India.[12-14] In the rst article, Marwaha et al indicate
the normal reference ranges of FT4, FT3, and TSH in
pregnant women, and used the 5th and 85th percentile to
dene the reference ranges in the disease-free subjects.
The authors report that the trimester-wise values in the
rst, second, and third trimesters were FT(3) (1.92–5.86,
3.2–5.73, and 3.3–5.18 pM/l), FT(4) (12–19.45, 9.48–19.58,
and 11.32–17.7 pM/l), and TSH (0.6–5.0, 0.44–5.78, and
0.74–5.7 IU/ml), respectively.[12] With regard to iodine
deciency during pregnancy, a hospital-based study from
Kolkata has suggested that pregnant women from their
center were iodine sufcient.[13]
In a large epidemiological study of 24,685 students from
all over India published in 2010, the authors attempted to
dene normative data on thyroid hormone levels in healthy
school children.[14] 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.[15] The authors
reported that for TSH, the 97th percentile was in the range
6.01–8.4 mIU/l for boys and 5.28–8.04 mIU/l for girls.[15]
This, as the authors themselves suggest, offers a compelling
argument against lowering the reference range of TSH in
this population.
communIty-Based ultRasound studIes
In IndIa
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.[16] In the state of Gujarat, the same group had
reported that iodine deciency continues to be a problem,
as more than 20% of the population had a very low median
urinary iodine of <50 µg/l.[17] In the same population, the
Figure 2: Histological type distribution of 1185 “new cases” of thyroid cancer.
Figure based on a table published by Gangadharan et al.[11] Anaplastic,
Cancer Not-Otherwise Specied and No histology proof-cases, together,
accounted for 223 cases in this survey
Unnikrishnan and Menon: Thyroid disorders in India
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Indian Journal of Endocrinology and Metabolism / 2011 / Vol 15 / Supplement 2 S81
prevalence of hypothyroidism has been reported to be
about 7%.[17] The use of ultrasound in population studies
of thyroid gland size is an exciting new area for research
in the eld of thyroid epidemiology.[18-20]
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Cite this article as: Unnikrishnan AG, Menon UV. Thyroid disorders in India:
An epidemiological perspective. Indian J Endocr Metab 2011;15:S78-81.
Source of Support: Nil, Conict of Interest: None declared.
Unnikrishnan and Menon: Thyroid disorders in India
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