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False certitude on salt and blood pressure
Table : Hypothyrold Infants identified by newborn screening
hypothyroidism distinguished by a low T4 and delayed TSH increase seems to be temporally related to the implementation of successful support measures for very-low-birthweight infants. Such infants, who had no chance of survival a decade ago, now have increasing opportunity to thrive. But with their survival, this cohort presents a set of issues and problems rarely associated with the typical hypothyroid child diagnosed by newborn screening. For example, will these very-lowbirthweight infants prove to have permanent or transient hypothyroidism? Will the delay in treatment further lessen their chances of a normal developmental outcome? What is the underlying cause responsible for the delayed TSH elevation? Is there any connection between iodine contained in cleansing solutions used in neonatal intensive care nurseries and thyroid failure? Answers to these and other questions will have to await the collection of more data and the careful follow-up of the children who comprise this unique group. In the meantime, it is essential that those involved with newborn screening programmes, especially programmes dependent on TSH as the primary marker, be aware of the potential pitfalls in diagnosis of hypothyroidism in such low birthweight infants. M L Mitchell, C Walraven, D A Rojas, K F McIntosh, R J Hermos New England Regional Newborn Screening Program, State Laboratory Institute, Jamaica Plain, MA 02130, USA
1
Mitchell ML, Potischman N, Larsen PR, Klein RZ. Atypical cases in a screening program for congenital hypothyroidism. In: Naruse H, Irie M, eds. Neonatal Screening. Amsterdam: Excerpta Medica, 1983: 95-100.
False certitude
on
salt and blood pressure
SIR-A consensus conference on sodium and hypertension was held on Oct 30,1993, in Freiburg. The intention was to find out what should be the recommended maximum salt intake in Germany. Scientists (mostly nutritionists) from the UK, Sweden, Canada, and the USA were invited to give lectures on recent epidemiological and intervention studies relating dietary sodium intake and high blood pressure. On the assumption that daily sodium intake averages 250 mmol there was amazing unanimity-this really is consensus-that salt restriction would lower blood pressure. Not only would most hypertensive patients benefit but also the whole population might gain advantage in terms of primary prevention of hypertension and its consequences. The number of lives saved via reduced mortality due to myocardial infarction and stroke would be in the thousands, according to an estimate based on epidemiological calculations, which has not yet been validated by any prospective clinical trial. I was surprised that the lecturers were all on one side of the controversy. The expression of more balanced views or of adverse evidence was carefully avoided. Even though a reduction of dietary salt intake by 100 mmol of Na and Cl,
corresponding to roughly 6 g of NaCl, is associated with a fall of merely 2 mm Hg in systolic and 1 mm Hg in diastolic blood pressure, and even though such a reduction cannot be achieved in the general population in the long-term, as shown by most intervention studies, the speakers remained undisturbed in their claim that salt intake should be reduced. Salt intake averages 8-9 g per day in western Europe, as demonstrated by INTERSALT five years ago,’ so a reduction to, say, 6 g is unlikely to achieve a decrease of more than 0-4 mm Hg systolic and 0 -2 mm Hg diastolic, and that reduction would be very hard to achieve. Even so, committed advocates of heavy salt restriction continue to try to change everybody’s dietary habits and charge the food industry with an irresponsible attitude to the entire population. The last part of this meeting was reserved for selected German-speaking participants. (Although I am of German origin and German-speaking my presence was clearly unwelcome. Presumably my presence threatened the consensus. Eventually I was allowed in but my interventions were not appreciated.) A previously prepared "consensus paper" was handed out and discussed. Its authors stated that the average salt consumption in Germany was 10-15 g, admittedly based on data gathered 15 years ago. INTERSALT showed that the populations of the three German centres that participated in this study had an average intake not exceeding 9 g (based on urinary Na), but it was difficult to get these data introduced into the consensus paper. The reason seems obvious. The goal was a decrease in salt intake to below 6 g. INTERSALT findings suggest that this would mean a further reduction by 3 g, which would probably not change blood pressure, yet be very hard to achieve.2 Other non-pharmacological approaches were ignored. So was overweight. The US body mass index in INTERSALT was as high as 29, and that of German participants was about 26. Body mass index and heavy alcohol intake were strongly and independently related to systolic and diastolic blood pressure in this study and in many others. Should salt really be top
priority? The result of the consensus debate-with not much discussion about the real issue, which is the feasibility and the potential benefits of such a severe salt restriction-was the authoritarian advice to the whole German population that salt intake must be reduced to less than 6 g per day. Instead, why not advise Germans to eat less and to drink less alcohol? There is no dispute about these two measures leading to better control of high blood pressure. Tilman B Drüeke INSERM Unit 90 and Department of France
1
2
Nephrology, Hôpital Necker, 75743 Paris,
Intersalt Cooperative Research Group. INTERSALT: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. BMJ 1988; 297: 319-28. Muntzel M, Drüeke T. A comprehensive review of the salt and blood pressure relationship (review). Am J Hypertens 1992; 5: 1S-42S.
61
hypothyroidism distinguished by a low T4 and delayed TSH increase seems to be temporally related to the implementation of successful support measures for very-low-birthweight infants. Such infants, who had no chance of survival a decade ago, now have increasing opportunity to thrive. But with their survival, this cohort presents a set of issues and problems rarely associated with the typical hypothyroid child diagnosed by newborn screening. For example, will these very-lowbirthweight infants prove to have permanent or transient hypothyroidism? Will the delay in treatment further lessen their chances of a normal developmental outcome? What is the underlying cause responsible for the delayed TSH elevation? Is there any connection between iodine contained in cleansing solutions used in neonatal intensive care nurseries and thyroid failure? Answers to these and other questions will have to await the collection of more data and the careful follow-up of the children who comprise this unique group. In the meantime, it is essential that those involved with newborn screening programmes, especially programmes dependent on TSH as the primary marker, be aware of the potential pitfalls in diagnosis of hypothyroidism in such low birthweight infants. M L Mitchell, C Walraven, D A Rojas, K F McIntosh, R J Hermos New England Regional Newborn Screening Program, State Laboratory Institute, Jamaica Plain, MA 02130, USA
1
Mitchell ML, Potischman N, Larsen PR, Klein RZ. Atypical cases in a screening program for congenital hypothyroidism. In: Naruse H, Irie M, eds. Neonatal Screening. Amsterdam: Excerpta Medica, 1983: 95-100.
False certitude
on
salt and blood pressure
SIR-A consensus conference on sodium and hypertension was held on Oct 30,1993, in Freiburg. The intention was to find out what should be the recommended maximum salt intake in Germany. Scientists (mostly nutritionists) from the UK, Sweden, Canada, and the USA were invited to give lectures on recent epidemiological and intervention studies relating dietary sodium intake and high blood pressure. On the assumption that daily sodium intake averages 250 mmol there was amazing unanimity-this really is consensus-that salt restriction would lower blood pressure. Not only would most hypertensive patients benefit but also the whole population might gain advantage in terms of primary prevention of hypertension and its consequences. The number of lives saved via reduced mortality due to myocardial infarction and stroke would be in the thousands, according to an estimate based on epidemiological calculations, which has not yet been validated by any prospective clinical trial. I was surprised that the lecturers were all on one side of the controversy. The expression of more balanced views or of adverse evidence was carefully avoided. Even though a reduction of dietary salt intake by 100 mmol of Na and Cl,
corresponding to roughly 6 g of NaCl, is associated with a fall of merely 2 mm Hg in systolic and 1 mm Hg in diastolic blood pressure, and even though such a reduction cannot be achieved in the general population in the long-term, as shown by most intervention studies, the speakers remained undisturbed in their claim that salt intake should be reduced. Salt intake averages 8-9 g per day in western Europe, as demonstrated by INTERSALT five years ago,’ so a reduction to, say, 6 g is unlikely to achieve a decrease of more than 0-4 mm Hg systolic and 0 -2 mm Hg diastolic, and that reduction would be very hard to achieve. Even so, committed advocates of heavy salt restriction continue to try to change everybody’s dietary habits and charge the food industry with an irresponsible attitude to the entire population. The last part of this meeting was reserved for selected German-speaking participants. (Although I am of German origin and German-speaking my presence was clearly unwelcome. Presumably my presence threatened the consensus. Eventually I was allowed in but my interventions were not appreciated.) A previously prepared "consensus paper" was handed out and discussed. Its authors stated that the average salt consumption in Germany was 10-15 g, admittedly based on data gathered 15 years ago. INTERSALT showed that the populations of the three German centres that participated in this study had an average intake not exceeding 9 g (based on urinary Na), but it was difficult to get these data introduced into the consensus paper. The reason seems obvious. The goal was a decrease in salt intake to below 6 g. INTERSALT findings suggest that this would mean a further reduction by 3 g, which would probably not change blood pressure, yet be very hard to achieve.2 Other non-pharmacological approaches were ignored. So was overweight. The US body mass index in INTERSALT was as high as 29, and that of German participants was about 26. Body mass index and heavy alcohol intake were strongly and independently related to systolic and diastolic blood pressure in this study and in many others. Should salt really be top
priority? The result of the consensus debate-with not much discussion about the real issue, which is the feasibility and the potential benefits of such a severe salt restriction-was the authoritarian advice to the whole German population that salt intake must be reduced to less than 6 g per day. Instead, why not advise Germans to eat less and to drink less alcohol? There is no dispute about these two measures leading to better control of high blood pressure. Tilman B Drüeke INSERM Unit 90 and Department of France
1
2
Nephrology, Hôpital Necker, 75743 Paris,
Intersalt Cooperative Research Group. INTERSALT: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. BMJ 1988; 297: 319-28. Muntzel M, Drüeke T. A comprehensive review of the salt and blood pressure relationship (review). Am J Hypertens 1992; 5: 1S-42S.
61