The Salt Sub-group of Scientific Advisory Committee on Nutrition (SACN) met in January 2002 to begin a review of COMA's 1994 recommendation that salt intake should not exceed 6 g/day, reports Reading Scientific Services.
The review involves the scrutiny of new evidence and the consideration of recommended salt intakes for children. Medline literature searches covered salt/sodium deprivation, adaptation to low sodium/salt intakes, salt/sodium conservation (for example during exercise or heat acclimation), salt/sodium restriction, sodium balance and salt sensitivity. The effects of chloride and the renal handling of salt/sodium in children were also searched.
The RSSL reports that the draft minutes of the meeting held on 18 April are of interest in that they deal with the matter of salt or sodium intakes in a manner far removed from the highly charged debate over dietary salt between pressure groups and representatives of the food industry. Apparently, more information is needed on the physiological requirement for sodium and low sodium intakes. This is because much of the work on sodium homeostasis has related to higher salt intakes. It was noted that the older scientific literature might give guidance on minimum safe intakes. Data is also sparse on physiological ranges of sodium required by infants, with much of the literature in the area being focussed on neonates and pre-term infants.
The relative importance of the chloride ion was also discussed with reference to work by Kotchen et al. which suggested that the chloride ion did not exert an independent effect on blood pressure, and in practice is always consumed as sodium chloride. Salt sensitivity is related to the kidney's ability to handle a sodium load, but the influence of age and genotype on this needs further research.
The RSSL reports that more data is needed on the relationship between dietary exposure to salt/sodium and different patterns of consumption of processed or fast foods, or of salt added during cooking and at the meal table. Apparently both the Food and Drink Federation and Verner Wheelock Associates have some information on this topic, to which the subgroup planned to ask for access.
Although morbidity and mortality studies have focussed on hypertension as an outcome of sodium intake, salt sensitivity is another possible outcome. It is noted that there is very little data on the relationship between salt and mortality or altered physiology. Work on early life experiences suggested that smaller babies had higher blood pressure in later life and exposure to sodium in early life might also increase the risk of developing high blood pressure in later life. However, these were just associations rather than evidence of cause and effect.
Overweight and obesity, inactivity and activity, glucose and insulin homeostasis, are all factors which affect blood pressure. Alcohol and smoking have effects too, as do potassium, calcium and magnesium. The relationship between these factors and sodium homeostasis in the development of hypertension also needs better evaluation. The RSSL concluded that SACN Salt subgroup is to meet again on 21 May 2002 after which it plans to put together a report on its findings.