Purpose It has been reported that the excretion of urinary uric acid is increased by the ingestion of bicarbonated salt spring water or bathing in radioactive spring water. Furthermore, uric acid is considered to play an important role in diminishing oxidative stresses. We therefore investigated the influence of bathing water on the excretion of uric acid from the aspect of urinary oxidation-reduction potential (ORP).
Methods 1. Nine volunteers (three males and six females) aged 22 to 26 were divided into three bathing groups: in sulphur spring water, in bicarbonated salt spring water, and in tap water. Urine specimens were taken six times from 0600 to 1600 while repeating bathing and taking meals alternatively at intervals of 2 hours. ORP, pH, and the concentrations of uric acid and creatinine in urine specimens were measured.
2. ORP, pH, and the concentrations of uric acid and creatinine were measured in the urine specimens taken from the seven subjects in the bicarbonated salt spring and sulphur spring bathing groups early in the morning everyday during the stay at the spa. In addition, serum uric acid levels were measured at the beginning and the end of the stay.
Results 1. The average ORP was 527mV in tap water, 407mV in bicarbonated salt spring, and 145mV in sulphur spring bathing. The urinary ORP increased obviously after bathing in tap water and decreased after bathing in sulfur spring water. The average urinary ORP was 257mV after bathing in tap water, 220mV after bathing in bicarbonated salt spring water, and 216mV after bathing in sulfur spring water. Urinary uric acid/creatinine ratio showed a significant and negative correlation with urinary ORP in all three kinds of water. Urinary pH after bathing varied randomly. Urinary uric acid/creatinine ratio exhibited a significant positive correlation with the urinary pH in all three kinds of water.
2. While serum uric acid elevated after a short stay at the spa of less than 10 days, it decreased after a long stay of more than 2 weeks.
Discussion and Conclusions Urinary ORP immediately reflected the ORP of bathing water. The urinary uric acid/creatinine ratio possessed a negative correlation with urinary ORP. Because the ORP of spring water is commonly lower than that of tap water, bathing in spring water may increase the excretion of uric acid and as a result, may lower the serum uric acid levels after the long stay at the spa. The urinary uric acid/creatinine ratio exhibited a significant positive correlation with urinary pH. The results suggest that if the urinary pH gradually becomes alkaline after a long period of ingestion of alkaline spring water, the excretion of uric acid will be promoted, resulting in a lowered serum uric acid.