Defining cooking salt intakes for patient counselling and policy making

The role of salt (NaCl) in the development of high blood pressure has been a matter of debate, however, the Intersalt Study showed that sodium (Na) intake in various areas of the World is related to the slope of blood pressure with age. Accurate amounts of the total salt intake or that coming from a particular source are needed, both, for physicians who need to consider the salt intake of their patients and for public health workers who are in charge of the implementation of public health programs where salt is used as a carrier of other nutrients. An analysis of the literature suggests that exaggerated values for total salt intakes have often been obtained from indirect estimates; discretionary salt use, i.e. home-cooking salt has invariably been overestimated. A method is described for measuring the contribution of cooking salt to total salt intake since it is a confusing area where inappropriate methods have been used to assess its contribution. The method described is based on the use of small amounts of lithium carbonate fused with NaCl. Validation experiments were undertaken to determine the naturally occurring lithium (Li) in a number of foods including fresh, frozen and tinned vegetables, and the use of Li tagged salt for cooking vegetables and for direct use in cooked foods. We also assessed whether Li was taken up proportionally with Na into foods during cooking. In general vegetables contained variable but only small amounts of Li except aubergine and spinach, and Li was taken up proportionally with Na in a variety of vegetables. Results showed that 36, 35 and 21% of the salt added during cooking was recovered in carrots, runner beans and potatoes respectively, the rest being discarded in the cooking water. This suggest that about a third of salt added during the cooking of vegetables will be ingested by the household. Attempts to rely simply on the total use of household salt supplies will clearly exaggerate, markedly, the true intake of individuals.