Successes and drawbacks in the caries-preventive use of fluorides--lessons to be learnt from history.

Water fluoridation was the first breakthrough in the practice of preventive cariology on a community level and has remained one of the cornerstones of prevention in dentistry. The concepts regarding the mechanisms of the caries-inhibitory effect, however, have changed in several respects. Today there is general agreement that topical effects on the erupted enamel are most important. The contention that there is no pre-eruptive effect whatsoever has created confusion; there is in fact evidence for a minor pre-eruptive protective effect. Around 1980 many experts believed that fluorides should not be used in high concentrations, for instance above those in dentifrices, because this could block remineralisation in the body of pre-cavity lesions. However, it is now known that such undesirable effects are negligible or non-existent. In the fifties and sixties, fluoride tablets were widely used in Europe and helped to make the concept of caries prevention popular. From 1980 onwards, fluoride dentifrices were found to have a much greater impact and were recognized as being able to lead to a decline of caries prevalence in entire countries, and fluoride tablets gradually lost their importance. Antifluoridationists were unable to delay or hinder the widespread use of fluoride toothpastes but in many cases have successfully opposed public health measures such as fluoridation of water or of salt. The spread of these methods, beneficial for all social strata, might have been more rapid if some of the experts had not propounded the erroneous supposition that fluoride dentifrice will be sufficient for caries prevention. Sale of fluoridated salt has been authorized in several countries on a nationwide scale. However, only Latin American countries have introduced salt fluoridation for entire populations. In Central and Eastern Europe where caries prevalence continues to be high and where the level of usage of topical fluorides including dentifrices will presumably remain at a low level for many years, salt fluoridation would be beneficial.

[Sodium and hypertension]. / Sodium et hypertension.

Over several million years the human race was programmed to eat a diet which contained about 15 mmol of sodium (1 g of sodium chloride) per day. It is only five to ten thousand years ago that we became addicted to salt. Today we eat about 150 mmol of sodium (9-12 g of salt) per day. It is now apparent that this sudden rise in sodium intake (in evolutionary terms) is the most likely cause for the rise in blood pressure with age that occurs in the majority of the world's population. Those which consume less than 60 mmol/day do not develop hypertension. The reason for the rise in sodium intake is not known but it is probable that an important stimulus was the discovery that meat could be preserved by immersion into a concentrated salt solution. This seemingly miraculous power endowed salt with such magical and medicinal qualities that it became a symbol of goodness and health. It was not until 1904 Ambard and Beaujard suggested that on the contrary dietary salt could be harmful and raise the blood pressure. At first the idea did not prosper and it continues to be opposed by a diminishing band. The accumulated evidence that sodium intake is related to the blood pressure in normal man and animals and in inherited forms of hypertension has been obtained from experimental manipulations and studies of human populations. The following observation links sodium and hypertension. An increase in sodium intakes raises the blood pressure of the normal rat, dog, rabbit, baboon, chimpanzee and man. Population studies have demonstrated a significant correlation between sodium intake and the customary rise in blood pressure with age. The development of hypertensive strains of rats has revealed that the primary genetic lesion which gives rise to hypertension resides in the kidney where it impairs the urinary excretion of sodium. There is similar but less convincing evidence in essential hypertension. The kidney in both essential hypertension and hypertensive strains of rats share a number of functional abnormalities most of which are capable of impairing sodium excretion. Essential hypertension would appear to be as much a renal disturbance related to the intake of sodium as hypertension secondary to renal disease.

A history of salt.

The medical history of salt begins in ancient times and is closely related to different aspects of human history. Salt may be extracted from sea water, mineral deposits, surface encrustations, saline lakes and brine springs. In many inland areas, wood was used as a fuel source for evaporation of brine and this practice led to major deafforestation in central Europe. Salt played a central role in the economies of many regions, and is often reflected in place names. Salt was also used as a basis for population censuses and taxation, and salt monopolies were practised in many states. Salt was sometimes implicated in the outbreak of conflict, e.g. the French Revolution and the Indian War of Independence. Salt has also been invested with many cultural and religious meanings, from the ancient Egyptians to the Middle Ages. Man's innate appetite for salt may be related to his evolution from predominantly vegetarian anthropoids, and it is noteworthy that those people who live mainly on protein and milk or who drink salty water do not generally salt their food, whereas those who live mainly on vegetables, rice and cereals use much more salt. Medicinal use tended to emphasize the positive aspects of salt, e.g. prevention of putrefaction, reduction of tissue swelling, treatment of diarrhea. Evidence was also available to ancient peoples of its relationship to fertility, particularly in domestic animals. The history of salt thus represents a unique example for studying the impact of a widely used dietary substance on different important aspects of man's life, including medical philosophy.