RELATIVE ADVANTAGES AND DISADVANTAGES OF PRESCRIPTIVE VERSUS POPULATION BASED PROPHYLAXIC MEASURES

Fernando E. Viteri¹

¹Dr. Fernando E. Viteri is Professor of Nutrition, Department of Nutritional Sciences, College of Natural Resources at the University of California, Berkeley, USA.

Dr. Hetzel's document on global strategy for the eradication of Iodine Deficiency Disorders (IDD) indicates a great variety of effects of iodine deficiency much more extensive than goitre even though this familiar feature is the obvious one. Even mild to moderate iodine deficiency may cause minor but important alterations in mental and sensory functions. Widespread mild to severe disability would not promise a productive life of good quality particularly in the developing world. Iodine supplementation has reduced goitre and cretinism in many parts of the world. Although it also increases survival rate, we should avoid falling into the trap that all that is important is survival per se without further attempts to ensure a productive and full life for those been 'survived'.

The widespread effectiveness of iodized salt (even where iodine deficiency is categorized as severe), if the programme is effectively conducted, is emphasized by Dr. Hetzel in this State-of the-Art-Paper. He has rightly dedicated paragraphs to the effectiveness of salt iodization in the control of IDD in an area of severe deficiency in China. Indeed, in Jixian, salt iodization solved the IDD problem. This proves that even in a population with 11.4% cretins an effective programme can correct very severe IDD. Also, one must not forget the proven efficiency of iodized salt in the control of cretinism in Europe. Yet, in order to control severe to moderate IDD, only iodized oil, orally or intramuscularly has been recommended. I believe that both methods of correcting IDD i.e. iodized salt and iodized oil either orally or intramuscularly, should be promoted and emphasized. Oral oil should be as effective as any other measure in correcting IDD and can be expected to meet the demands of even severe iodine deficiency, if compliance at the population level is good and the programme is not only directed at school children. It should be indicated that with adequate production of oil specifically for oral adminstration the cost would decrease to one tenth of what presented in Table 18 of this document. Also I include in the costs the cost of staff time in all the programmes including staff time for surveillance of the programmes. With regard to dietary diversification, which as Dr. Hetzel clearly indicated, through economic development has been responsible for the disappearance of IDD in Western countries, one should also stress the importance of programmes of iodization and dietary diversification together with other public health programmes. How important a decline in the consumption of goitrogens may be under these circumstances is yet to be defined. While it seems to me that in this document the prescriptive method of IDD correction is emphasized more, i.e. iodized oil, I still think that iodization of salt and other similar measures should be the first method of choice. However, the use of iodized oil by mouth or by injections offers another effective alternative for severe iodine deficiency if the cost of production can be reduced and a system to assure vide coverage can be established and supported. Severe IDD require either an effective and well controlled iodized salt programme or the adminstration of iodized oil either orally or by intramuscular injection to all of the population. Priority groups for initiation of iodized oil by intramuscular injection can be children and women of reproductive age.

The prescriptive approach can have the advantage as well as the limitation that it can be carried out through the health care system and will function only as well as this system can cover the whole population. It may appear that, in contrast to population based measures, i.e. iodized salt, it does not require the cooperation and enforcement of other government departments and private industry. This is not the case. If the population cooperates, if governments and private sectors join efforts in providing universal coverage of prescriptive (mainly iodized oil) methods, these measures are effective. Prescriptive measures are to be given more serious consideration than in the past where the tendency has been to think only of iodized salt and other alternatives have not been heard of. This approach to the eradication of IDD is effective when all of the population can be reached by a team of health workers, therefore it requires excellent population coverage which then becomes extremely expensive because often those in greater need are the hardest to reach and to convince of the benefits of an oil injection. We cannot compare immunization programme coverage to that required to eliminate IDD by iodized oil injection. In the first case 85-90% coverage is more than enough; in the second case it is not adequate. The use of iodized oil by injection to eradicate IDD in large countries, therefore, poses serious logistic and financial problems. Either method of control and prevention demands a concentrated effort for the complete prevention of central nervous system defects. In certain countries more efficient schemes for the production and distribution of iodized salt need to be established, since although guidelines are set, the problem has remained as to how make them appropriate for certain conditions in several countries.

In the section on Central and South America, Dr. Hetzel has provided more up-to-date information on why some of the programmes in Latin America have not been as successful as they should have been, based on the 1983 Lima Conference entitled 'Towards the eradication of endemic goitre, cretinism and iodine deficiency'. So far in Latin America many iodized salt programmes have shown partial but substantial success. In this region there are no grounds by which iodized oil adminstration (intramuscularly or orally) can be judged at the general population level. One thing is to carry out a pilot study as has been the case of Bolivia, Peru and Ecuador with iodized oil, and another one is to convert this programme into a national one.

Although there are still unsolved problems in ensuring adequate quality of iodized salt in sufficient amounts to be produced and distributed to massive iodine deficient population in many countries, these can be overcome. The reasons for a decline in total actual production of iodized salt in India and Nepal together in 1978-79 compared with 1974-75, as shown in Table 14 of Dr. Hetzel's document should be explored and corrected. Surveillance of an iodization programme should include monitoring of salt sales, checks on the iodine content of salt at the production sites and in the retail stores, monitoring of goitre prevalence in school-aged populations and analysis of the urinary iodine excretions. To get iodine into iodine deficient population, by either of these methods, can prove difficult in remote and isolated areas with IDD problem. In Bolivia llama are often used to transport salt and other goods. In the remote part of this country locally produced salt (extracted from large salars) makes the commercialization of iodized salt very difficult. In Sahel camels are used as usual system to transport goods. However, while salt in these areas is to be transported by camels in the programme of salt iodization, similarly people and equipments need to be transported in this way in the case of iodized oil injection.

Another problem associated with salt iodization is loss of iodine from such salts during storage. This depends on the handling and storage conditions. As it can be seen in Table 15 of Dr. Hetzel's document, keeping salt in covered areas, even when only the top is covered effectively prevents iodine loss. The loss of 16.4% in top covered salt which occurred when there were 434 millimeters of rain in 55 days is still acceptable. Note that this has been really heavy rain compared to other figures. In some countries effective life of salt iodization plants might have only been two to three years. However there are many iodization plants in Central and South America which have been working for over ten years without problems. Moreover, as I indicated there are easy solutions to this problem. There are many systems by which salt can be iodized and there are systems which have overcome technical problems.

In terms of iodine availability to the thyroid and the danger for transient thyrotoxicosis among individuals with nodular goitres or presenting single thyroid nodules without goitre, I do not understand the rationale behind administrating only 0.2 ml. of iodized oil since still 95 milligrams of iodine even with a relatively slow release from the site of injection would amply saturate thyroid needs of overproduction of thyroid hormones. I suggest explaining the rationale and the proof for suggesting this specific dosage. The condition of thyrotoxicosis, as stated by Dr. Hetzel, can be readily controlled with drugs like antithyroid or radioiodine ; experience in Costa Rica showed that during the transient thyrotoxicosis that occurred in that country, Reserpine was extremely effective in controlling the temporary problem.

Spontaneous remission is the norm for this type of thyrotoxicosis. Because of the small risk of transient thyrotoxicosis when compared to the general benefits of iodization programmes to the populations as a whole, it may not be necessary to avoid iodization in those over the age of forty years.

The monitoring of neonatal T-4 is ideal and highly desirable, but not necessary for the monitoring and evaluation of IDD programmes. If iodine excretion in the urine is adequate and there is no goitre, neonatal T-4 determinations may not be necessary for surveillance of the programme. I think that T-4 determinations in neonates should ideally be done in every newborn throughout the world but for other reasons. Since they are not only costly but you need good laboratory facilities to have reliable information. The impossibility of doing reliable T-4 determinations should not impair any actions to diagnose and correct IDD.

The more severe the problem, the greater the insurance needed to have a full and continuous coverage of the population in terms of adequate iodine intake or content in their body. The method is immaterial in my mind; however, I suspect that to achieve the universal coverage needed with iodized oil injections will be extremely difficult and expensive.