[Background and Purpose] Salt reduction is effective for preventing and improving hypertension, but the actual reductions in the salt intake among those on reduced-salt diets are not well known. We compared the amount of salt intake, nutrients and food composition among two groups-those reporting that they were on a reduced-salt diet (RSD) and those reporting that they were on a normal diet (ND). [Methods] A total of 1, 145 Japanese men and women aged 40-59 years old completed the self-administered questionnaires. Salt intake was assessed through two 24 hour urine collections and four dietary surveys based on 24 hour recall. [Results] Thirty-six subjects reported that they were on a reduced-salt diet. The estimated mean salt intakes after adjusting for sex, age, and BMI derived from sodium excretion into urine were 10.5 ± 0.5 grams and 11.5 ± 0.1 grams (means ± standard errors) for subjects on RSD and ND respectively (p=0.04). The salt intakes estimated from 24 hour recall were 10.0 ±0.5 grams and 11.9 ± 0.1 grams (means± standard errors) for RSD and ND respectively (p<0.001). Additional adjusting for energy-intake also showed the same trends. Subjects on RSD consumed 200kcal less total energy, but the energy composition did not differ significantly between the two groups. Those on a reduced salt diet ate significantly less amounts of grains and processed foods. [Conclusion] We confirmed that those who regarded themselves on the reduced-salt diet actually did take significantly less amounts of salt than those on a normal diet. However, the average salt intake for subjects on RSD did not reach the nationally recommended level of less than 10 grams of salt per day, with only 41.6% of the subjects on RSD achieving it.

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For prevention and management of hypertension, decreasing salt intake and increasing potassium intake are very important. To attain this objective, there is a need to be able to measure daily salt and potassium intake easily at home.
As most of these electrolytes are excreted in urine, we used overnight urine for 250 subjects. Regression analyses were performed to estimate 24-h urinary salt (NaCl₂₄) and potassium (K₂₄) from overnight (about 8 hour) urinary NaCl (NaCl_n) and potassium excretion (K_n) which was measured using an ion electrode method. The correlation coefficient between the NaCl₂₄ and NaCl_n, K₂₄ and K_n was 0.75 (p<0.001, n=250) and 0.71 (p<0.001, n=250) respectively. The formula of NaCl₂₄=1.95NaCl_n +4.54 (g/day) and K₂₄ =2.32Kn+1.03 (g/day) were derived.
The new salimeter utilized in this study consists of a conductivity meter for measuring overnight urinary NaCl concentration, electrical resistance for measuring overnight urinary volume in a 1L urine cup, a central processor unit in which the above formula was installed and a display panel showing the predicted NaCl₂₄ as a digital value. The correlation coefficient between the true NaCl₂₄ and NaCl₂₄ estimated by the new salimeter was 0.71 (n=159, p<0.001). The new salimeter could roughly estimate NaCl₂₄ with ease and would be useful for self- monitoring of daily salt intake.
Concentrations of NaCl and potassium of overnight urine were effectively measured using the compact salimeter C-121 and compact potassium ion meter (HORIBA) using a flat type ion electrode, although it was necessary to incorporate a correction formula when using undiluted urine.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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