Abstract
The body’s water and sodium balances are tightly regulated and monitored by the brain. Few studies have explored the relationship between water and salt intake, and whether sodium intake with different levels of fluid intake leads to changes in hydration status remains unknown. The aim of the present study was to determine the patterns of water intake and hydration status among young adults with different levels of daily salt intakes. Participants’ total drinking fluids and water from food were determined by a 7-day 24-h fluid intake questionnaire for 7 days (from Day 1 to Day 7) and duplicate portion method (Day 5, Day 6 and Day 7). Urine of 24 h for 3 days (Day 5, Day 6 and Day 7) was collected and tested for the osmolality, the urine-specific gravity (USG), the concentrations of electrolytes, pH, creatinine, uric acid and the urea. The fasting blood samples for 1 day (Day 6) were collected and measured for the osmolality and the concentrations of electrolytes. The salt intakes of the participants were evaluated from the concentrations of Na of 24 h urine of 3 days (Day 5, Day 6 and Day 7). Participants were divided into four groups according to the quartile of salt intake, including the low salt intake (LS1), LS2, high salt intake (HS1) and HS2 groups. In total, 156 participants (including 80 male and 76 female young adults) completed the study. The salt intakes were 7.6, 10.9, 14.7 and 22.4 g among participants in the four groups (LS1, LS2, HS1 and HS2 groups, respectively), which differed significantly in all groups (F = 252.020; all p < 0.05). Compared to the LS1 and LS2 groups, the HS2 group had 310–381, 250–358 and 382–655 mL more amounts of water from the total water intake (TWI), total drinking fluids and water from food (all p < 0.05), respectively. Participants in the HS2 group had 384–403, 129–228 and 81–114 mL more in the water, water from dishes and staple foods, respectively, than those in the groups of LS1 and LS2 (p < 0.05). The HS2 group excreted 386–793 mL more urine than those in the groups of LS1 and LS2 (p < 0.05). However, regarding urine osmolality, the percentage of participants with optimal hydration status decreased from 41.0% in LS1 and LS2 to 25.6% in the HS2 group (p < 0.05). Participants with higher salt intake had higher TWI, total drinking fluids and water from food. Nevertheless, they had inferior hydration status. A reduction in salt intake should be encouraged among young adults to maintain optimal hydration status.
Highlights
The body’s water and sodium balances are tightly regulated and monitored by the brain, including thirst, the regulation of water, electrolyte excretion or retention by the kidneys [1]
The current study showed that participants with different salt intake had different intakes of food, which increased from 1292 g in low salt intake 1 (LS1) group to 1859 g in high salt intake 2 (HS2) group (F = 24.816, p < 0.001)
The findings revealed that young adults with higher salt intake may partake in a greater consumption of water from food; the amounts of the total water intake (TWI) were higher than their counterparts
Summary
The body’s water and sodium balances are tightly regulated and monitored by the brain, including thirst, the regulation of water, electrolyte excretion or retention by the kidneys [1]. Studies have shown that dehydration, which was defined as less water intake than water loss, impeded cognitive performances, attenuating vigilance, attention and working memory [2]. Overhydration, defined as more water intake than water loss, can result in headache, nausea and memory loss [3]. To maintain vital functions, including proper blood volume and blood pressure, human cells require about 0.5 g/day of sodium. The main physiological function of sodium is to maintain positively charged ions in extracellular fluid, which participate in water metabolism, ensure the balance of water in the body and maintain the balance of acid and alkali in the body. Studies have shown that insufficient water intake increased the plasma salt level and osmolality. It is of vital importance to maintain the proper consumption of water and sodium for the human body
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