Biological effects of the hot-spring waters are considerd to be a sum effect resulting from the constituents of spring waters which act under either competitive or cooperative relationship between each ion, thus effect of one or two constitutents being not definitely attributable.
Entrance of these constituents into the body occurs as well by bathing or inhalation as by drinking the hot-spring waters. This has been known for a long time as for the gaseous substances. Isotope technique revealed that many minerals enter as well.
It is not feasible, however, to show biological effects of these incoming substances, because some of these substances are abundantly existing in the body originally. In addition, resulting effects may be altered by the autonomic nervous function or endocrine function which may be simultaneously activated by application of hot-spring waters.
On the other hand, some metallic substances such as Zn or Cu in spring water existing in a slight amount are considered to show a detectable effects, because, in general, the amounts of them are slight in the body and the biological effects are significant, some of them being known to act as co-enzyme.
Percutaneous absorption of radio-active Zn, added to a hot-spring water, was studied on mice and it was found that Zn behaves like other cation.
After single bathing, however, the amount absorbed was not allways dependent on pH of spring waters.
Regardless of what kinds of spring waters were used, the entered Zn was found in a higher concentration in the prostate, pancreas, adrenal gland and blood. This may show that Zn is apt to accumulate in these organs where a larger amount of Zn is originally contained and turn-over rate of the substance is rapid.
It may be resonable to assume that an existence of large amount of a substance in a certain organ or tissue is responsible for its function.
Absorbed metallic substances which accumulate in a particular organ, even in a slight amount, may exert an activating effect on the function of the organ.
Though biological activities of some substances have been studied by eliminating the substances from diet, the activating threshold of substances contained in spring waters are entirely unknown.
An attempt was made to elucidate the effects of a substance added to the hot-spring water of which chemical components and biological effects are well known. Inorganic compounds of Zn, Cu, Co, Fe, Mn and Mg were thus investigated. Various amounts of the substances were tested up to the maximum amount which had been ever estimated in any spring water in Japan. Groups of volunteers unaccustomed to hot-spring bathing were subjected to bathing in thus treated Onken hot-spring water and resulted effects were observed.
The results obtained on Zn showed that optimal corticoids-effect was expected when Zn was added in an amount of 100mcg/kg, When 300-5, 000mcg/kg of Zn was added, a moderate hypoglycemic effect ensued.
Addition of Cu ion in an amount of some mg/kg of the spring water resulted in the corticoids-effect. A limited amount of nearby 500mcg/kg of Cu was presented for lowering the blood sugar levels and activating the hematopoesis.