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National Consultation
on “Benefits and Safety of Iodised Salt”
Magnitude of IDD
in
In India, Iodine Deficiency
Disorders (IDD) are present throughout the country. Out of 275 districts surveyed
by Government of India institutions, Indian Council of Medical Research and
Central Goitre Survey Teams in different States and Union Territories, 235 have
been found to be endemic for iodine deficiency disorders (Table I and II) (1,
2).
Deficiency of iodine, which
is among the body’s essential micronutrients, is both easy and inexpensive to
prevent. Iodine is an essential element for normal growth and development in
animals and humans. It is required for synthesis of the thyroid hormones i.e.,
thyroxine (T4) and tri-iodothyronine (T3).
Thyroid hormones bring about a wide variety of vital physiological
processes such as early growth and develop-ment of the brain and body in man.
Scientific studies in India and elsewhere have shown that nutritional iodine
deficiency causes deficiency of thyroid hormones during foetal life and
childhood. A normal healthy thyroid
gland of an adult human contains 8-12 mg iodine. This can be reduced to as low as 1 mg or less in iodine deficient endemic
areas (3).
Iodine deficiency not only
causes goitre; it can also result in impaired brain development in the fetus
and infant, and retarded physical and psychomotor development in the
child. It also affects reproductive
functions and impairs children’s learning ability. The cumulative impact of nutritional iodine
deficiency results in compromised socio- economic development in the affected
communities. Iodine deficiency is the most common cause of preventable mental
retardation in the world today (4).
Use of Iodised
Salt in Prevention of IDD
In the last 50 years, many
countries in North America, Asia, Europe and Oceania have successfully
eliminated IDD, or made substantial progress in their control, largely as a
result of salt iodisation with potassium iodide or potassium iodate and through
dietary diversification. For example, in
In India, keeping in view
the magnitude of the problem and technical, administrative, financial and
operational feasibility on the recommendations of the Central Council of Health, Government of
India in 1984, took a policy decision
for USI i.e. all edible salt in the
country would be fortified with iodine (1).
Substantial progress has been
made in the country in the production of iodised salt from 3 Lakh MT in 1983 to
nearly 40 Lakh MT in 1997. Similarly, recent IDD surveys conducted by the
various institutions have revealed that more than 70% of population is
consuming iodised salt (9). Concurrently, the total goitre prevalence and
incidence of neonatal hypothy-roidism have also reduced (10). Further,
estimation of urinary iodine excretion levels amongst population in different
states indicate adequate iodine intake (10,11,12,13,). All these findings have
been further substantiated by reports on
iodine content of salt samples analysed and received from differentstates through Monitoring Information System (MIS) of Salt
Department and increase in production and supply of Iodised Salt (Table IV).
These findings indicate successful implementation of USI programme in India
(9). Recently, the scientific journal “Nature Medicine” has commended the
Indian salt iodisation programme as one of the most successful preventive
public health programme amongst the developing countries (14).
Recommended
Dietary Allowances of Iodine
Iodine requirements have
been calculated based on (a) average daily loss of iodine in the urine which is
100-200 mcg/day and (b) balance studies to attain a positive balance which is 44-162 mcg/day (3).
Based on scientific studies of iodine balance
over a 24 hour period, a safe daily intake of iodine has been estimated
to be between a minimum of 50 mcg and a maximum of 1000 mcg (15, 16). A
generally accepted desirable adult intake is 100-300 mcg/day. At all intake
levels of iodine, a proportionate amount of iodine is excreted in the urine,
which is the biochemical basis for assessing iodine status (17).
The Recommended Dietary
Allowances (RDA) for various age groups at global level are depicted in the
Table VA and VB. The RDA for iodine as recommended by joint consultation of
WHO/UNICEF/ICCIDD in 1996 has been given in Table VI (18). The RDA for iodine
for Indian population is 150 mcg per day.
Iodine Toxicity
Iodine has relatively wide
margin of safety. Acute andchronic toxicity studies with sodium iodate have been
carried out. Results of these long-term
experiments of administration to man and to animal of doses comparable to those
which are used in prophylaxis have failed to produce toxic signs (19). On the
basis of toxicological studies it has been confirmed that potassium iodate is
very safe at the level used in salt
iodisation (20). This has been confirmed
on the basis of worldwide experience of salt iodisation programme.
Iodine intake in USA and
Canada
In the United States of
America, potassium iodate is used as dough conditioner in bread making. Under
Food and Drug Administration (FDA) Regulation No. 17, potassium iodate
or potassium bromate, calcium iodate and/or calcium peroxide (21) are used in
bakery products at a maximal concentration of 0.0075%, that is, 75 parts per
million by weight of flour alone. The
FDA regulations (FDA : 121.101) also permit the addition of potassium iodide to
table salt for fortification upto a maximum concentration of 0.01%. As both bakery products and table salt are
meant for human consumption, and the maximum permissible limits are 75 parts
per million of potassium iodate and 100 parts per million of potassium iodide,
it can be concluded that within these specified limits of the FDA, the salts
are safe for human consumption (21).
In 1970, the Food and
Nutrition Board of the National Academy of Sciences, estimated that a daily
intake of 1000 mcg of iodine is safe (22). In 1980 American Medical Association
noted that no adverse physiologic reactions were observed with iodine intake up
to 1000 mcg per day in healthy adults (23).
Current
estimates of daily iodine intakes in Canada and the USA are substantially above
physiological need and are in the range of 460 mcg/day among 9-16 years old
children, to greater than 1 mg/day among as many as 10-20% of adults (24). With a level of iodisation that provides
these populations approximately 250 mcg/day of iodine from salt, it is thus
apparent that much of the intake comes from non salt sources (3).
Iodine Intake in Japan
Average daily intake of
iodine in Japan has been reported to be 3000 micrograms which is 20 times more
than the RDA value of 150 mcg in India.
Studies carried out in normal Japanese population have shown that they are
biochemically and clinically eumetabolic in spite of the consumption of large
amounts of iodine. The values for their
thyroid hormone are not different from those in non-endemic areas of other
countries indicating their adaptation to excess iodine intake (24, 25). Existence of this type of adaptation has also
been confirmed by animal experiments. There is little indication that iodine in
the amounts noted influences the prevalence of any of the thyroid diseases
(23).
Normal population and Iodised Salt
The average daily salt
intake in India is 10 g per day.
Consumption levels are within the 5-15 g/day range for children and adults. As
per Government of India recommendations the level of salt iodisation (quantity
of iodine added to salt) should provide
a minimum of 150 mcg of iodine per day at the consumption level (26). This recommendation accounts for the usual climatic factors like
heat and humidity, whichcan affect retention of
iodine in the salt. The use of potassium iodate has been preferred in India since it is more
stable than potassium iodide under our tropical climatic conditions. Moreover because iodate, on ingestion, is
very rapidly reduced to iodide and hence its use in iodised salt is equivalent
to use of potassium iodide.
From the average daily
intake of 10 g iodine fortified salt, the estimated availability of iodine
would be 150 mcg, of which about 30% is lost during cooking. The remaining 105 mcg is ingested and from
this about 70% is absorbed by the body.
This means approximately only 73.5 mcg is absorbed per day from iodine
fortified salt. This quantity when added
to the iodine daily consumed through food will be broadly comparable to the
daily physiological need of the body (3). Indeed urinary iodine excretion studies in the post iodisation phase show
that all over the country, the level achieved following salt iodisation is not
more than 300 mcg per day. Thus, the level of salt iodisation is totally safe
in our country.
Adverse Reactions to Iodised Salt
Including Risk of Iodine Induced Hyperthyroidism
Since iodine, when ingested
in large amounts, is easily excreted in the urine, iodine intake even at very
high levels (milligram amounts) can be safe. It is documented scientifically
that through adaptive mechanisms, normal people exposed to excess iodine remain
euthyroid and free of goitre.
It is not correct to
attribute skin reactions such as rashes
and acne to iodized salt. Physiological levels of iodine intake do not cause
“Iodism”. For example, among 20,000 childrenin the
USA suffering from allergy during the period 1935-1974, not a single case was
reported of allergic hypersensitivity to iodine in food. Following a publication, in Annals of
Allergy, of a request for notification of allergy to iodine, not a single
report was recorded between 1974 and 1980 (27).
However, high intakes of dietary iodine may induce hypothyroidism in
autoimmune thyroid diseases and may inhibit the effects of thionamide drugs
(28).
Iodine-induced
hyperthyroidism is an adverse effect which may occur primarily in older
people when severely iodine deficient populations increase their iodine
intake, even when the total amount is within the usually accepted range of
100-200 mcg/day. Epidemiologically
iodine-induced hyperthyroidism represents a transient increase in the
incidence of hyperthyroidism, which disappears in due course with the correction
of iodine deficiency (29).
Iodine induced hyperthyroidism occurs in some people
who have pre-existing autonomous nodular goitre. It appears likely that some
patient with latent Graves disease are
also at risk. The number of people at risk of iodine-induced hyperthyroidism is
directly proportional to the number of subjects with nodular goitre. The
occurrence of iodine-induced hyperthyroidism is probably related to the
relative increase and rapidity of increase of iodine intake, which occurs when
iodised salt is introduced in populations that have been severely iodine
deficient. There is no level of iodine in salt that offers complete protection
against some increase in the incidence of hyperthyroidism in a previously
iodine-deficient population. From a
public health point of view, the benefits of correcting iodine deficiency
through USI greatly outweigh the risk of iodine-induced hyperthyroidism
(29). A comparativeaccount of various levels of iodine intake to the
functional status of the body as a dose response curve is depicted in figure
1. From this a daily intake in the range
of 150-300 g is absolutely safe (30).
Conclusion
Daily iodine intake of upto
1 mg i.e. 1000 mcg, appear to be
entirely safe. Iodization of salt at a
level that assures an intake of 150-300 mcg/day keeps iodine intakes well
within daily physiological needs for all populations, irrespective of their
iodine status. In
Issues relating to the
safety of Universal Salt Iodization were carefully examined by eminent Scientists, Programme Planners, Managers and
Administrators for preparing national consensus document on Benefits and
Safety of Iodised Salt. Based on hard scientific evidences and data, it was concluded that USI is the most
appropriate and safe public health measure for eliminating IDD in
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APPENDICES
Appendix I
Selected Research Papers/
Studies Conducted in
Click to see details of the TABLES
Click to see details of the RESEARCH STUDY DATA
Click to see details of the RESEARCH STUDIES