Salt restriction affects the excretions of minerals (Na, K, Ca, Mg, P and Zn) in the second voided fasting early morning urine

The plasma concentrations of mineral (sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), and zinc (Zn)) are kept within narrow ranges to maintain homeostasis; hence, it is difficult to use them as indicators of nutritional status. We selected the excretion of these minerals in the second voided fasting early morning urine (EMU) as potential indicators of nutritional status. We previously reported that Na restriction caused a negative balance of Ca and Mg. Therefore, Na restriction can cause changes in EMU-minerals. This study aimed to examine the relationship between dietary Na restriction and urinary mineral excretion. The study lasted for 21 d, including 16 d of balance period and 3 d of recovery period. The participants (11 healthy young women) were divided into the Na restriction group (n=5) (NaCl: 6 g/d) and control group (n=6) (NaCl: 12 g/d). The Na restriction group changed to the control diet (NaCl: 12 g/d) during only the recovery period. The EMU-Na, Ca, Mg, P and Zn in the Na restriction group significantly decreased compared with that of the control group. The EMU-Na, K, Ca, Mg, and Zn in the group with NaCl intake of 6 g/d significantly decreased compared with that of the group with NaCl intake of 12 g/d (in the Na restriction group). We conclude that the decrease in excretion of Na, Ca, Mg and Zn in the EMU can lead to Na restriction. This result can serve as basis when considering EMU as an indicator of mineral status.