Family Practice Vol. 16, No. 3, 316
© Oxford University Press 1999
Book Reviews |
Salt, diet & health: Neptune's poisoned chalice: the origins of high blood pressure.
Reader in Epidemiology, Department of Environmental and Preventive Medicine, Wolfson Institute of Preventive Medicine, St Bartholomew's and The Royal London School of Medicine and Dentistry
GA MacGregor, HE de Wardener. (241 pages, £14.95 paperback, £40.00 hardback.) Cambridge University Press, 1998. ISBN 0-521-63545-4 paperback, 0-521-58352-7 hardback.
This book will be intelligible to a lay readership, so should have wider appeal than the nutritional or physiological interests its title might suggest. For those interested in social history, salt has touched on a wide range of human activities. Stone-age man ate little salt—less than a tenth of the present Western average of intake 10 grams (2 teaspoons) per day—and ancient languages had no word for salt. The book traces the substantial increase in salt consumption some five to ten thousand years ago, arising from the need to preserve meat over winter when human populations ceased nomadic existence and took up farming. The accidental discovery that soaking meat in brine preserved it over the winter months had a profound effect on human history.
Salt became essential to survival and developed important symbolic associations—it was "especially dear to the gods" (Plato), the apostles were "the salt of the earth". It was a symbol for purity, which in turn may have led to its early positive associations with health; the Latin word for salt (salsas) derives from the word for health (salus). Associations with wealth (salary) developed and industrial salt production led to the development of entire cities (Chester in England). The wealth of such cities led variably to notoriety (Sodom and Gomorrah) or artistic beauty (Venice). Salt was heavily taxed (at a level that makes the present tax on cigarettes look paltry), and Gandhi complained of the British in India that "they even tax our salt—a necessity of life only less necessary than water and air".
The history of the measurement of blood pressure is presented: from Reverend Stephen Hale's measurement of blood pressure by cannulating an artery in a mare in the 1730s, the earliest conventional mercury sphygmomanometer by Rocci in 1896, the sounds described by Korotkoff (a Russian army surgeon, who despite later uncertainty described clearly that diastolic pressure corresponded to the point when the sounds cease), to the development of recent 24-hour ambulatory monitoring. Important animal experiments are outlined, from Dahl's rats in the 1950s to Denton's recent work with chimpanzees. A few chapters cover the important relationship between salt, blood pressure and cardiovascular disease, while a further chapter covers the less familiar relationship of salt to other diseases including asthma, stomach cancer, osteoporosis and kidney stones, as well as heart failure and other conditions related to fluid retention. (The high salt diet in Western populations means that we are all waterlogged to the extent of at least a litre.)
Further chapters discuss the addiction (not too strong a word) that developed to the large amounts of salt added to food, with historical examples of the lengths people have gone to obtain it. Man's resourcefulness in extracting salt from the earth is considered with many examples. The final chapter covers the activities of the food industry (and especially the salt industry) in opposing moves to reduce the high salt content of processed food. An appendix presents practical information on the interpretation of food labels and methods of reducing dietary salt. Overall this is a valuable reference on the wide-ranging implications of our use of salt.
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