(Patho)physiological implications of chronic dietary sodium restriction during pregnancy; a longitudinal prospective randomized study. Preferred salt levels and salt taste acuity in human subjects after ingestion of untasted salt.
To study the possible pathophysiological implications of long continued dietary sodium restriction in pregnancy.
                Longitudinal prospective randomized study of the effects of a low sodium diet compared with unrestricted sodium intake in pregnancy.
                Academic Department of Obstetrics and Gynaecology at Sint Radboud Hospital, Nijmegen, The Netherlands.
                42 healthy nulliparous women.
                A low sodium diet (20 mmol sodium daily) started in the 14th week of pregnancy and stopped after delivery.
                Maternal weight gain, food intake, blood pressure, cardiac output, systemic vascular resistance, haematocrit and birthweight.
                Total maternal weight gain and dietary energy intake during pregnancy and weight at 1 and 6 weeks postpartum were significantly lower in the low sodium group. Blood pressure during pregnancy did not show major differences. Stroke volume and cardiac output during pregnancy were significantly lower in the low sodium group whereas systemic vascular resistance was significantly higher. Haematocrit values in the low sodium group tended to be lower during pregnancy, but were significantly lower at 1 and 6 weeks postpartum than in the unrestricted group. Placental and birthweights were not significantly different between the two groups.
                Chronic dietary sodium restriction during pregnancy is characterized by a diminished body fat accumulation and a reduction in circulating volume, due to a decrease in both plasma and red cell volume, in combination with a high systemic vascular resistance without major effects on blood pressure and birthweight. We have examined whether salt loading alters the salt preference or salt taste acuity of nine human subjects on continuous low salt diet. Subjects were randomly assigned to either untasted salt tablets (120 mmol/day) or placebo over a 2-week period at the end of which salt preference and salt recognition thresholds were measured. Subjects then received the alternate substance for another 2 weeks and the measurements were repeated. While urinary Na+ and Cl- were significantly increased while on salt tablets, urinary volume, K+, urea and creatinine concentrations, blood pressure, body weight, salivary and plasma electrolyte concentrations were unchanged. Plasma renin and aldosterone levels were reduced while on salt tablets but not significantly. Salt tablets caused a significant increase in sodium recognition threshold but a significant decrease in salt addition to unsalted tomato juice and in ideal salt level assessed by presalted (150 mmol/l) tomato juice. Thus, an increase in untasted dietary salt may reduce salt preference in human subjects, a finding opposite to that with an increased, tasted salt intake over a similar period.
Salt consumption during pregnancy should remain a matter of personal preference.