DIURNAL-VARIATION OF PLASMA MINERALS AND TRACE-ELEMENTS IN A GROUP OF JAPANESE MALE-ADULTS

When the nutritional status of minerals and essential trace elements is assessed by their levels in plasma, intra-individual variation in the measured values, particularly diurnal variation, must be considered. In this paper, concentrations of nine elements (Na, Mg, P, K, Ca, Fe, Cu, Zn, and Se) in plasma collected 7 times in a 24-h period from 10 healthy Japanese adults were measured with hemoglobin and plasma concentrations of proteins (total protein, albumin, retinol binding protein (RBP), ceruloplasmin, and transferrin), total cholesterol, and cortisol. Then the pattern of diurnal variation in, and the interrelationships among, these parameters were clarified in subjects who consumed an ordinary meal. Significant diurnal variation examined by two-way analysis of variance (variations due to subject and sampling time) was found for Zn, RBP, and cortisol. Plasma Zn level was higher in the forenoon samples than in those taken in the afternoon. The pattern of diurnal variation found for cortisol was similar to, but slightly different from, that for Zn. The correlation coefficient between Zn and cortisol was significant (r=0.555) using the standardized values for individuals, and in the result of multiple regression analysis, cortisol level was selected as the significant explanatory factor for Zn variation; however, the sampling time was the most significant factor. For other elements besides Zn, no significant diurnal variation was found. Moreover, no meaningful factors were selected for variations of those elements in the result of multiple regression analysis. These results indicate that, in assessing Zn nutriture with its plasma levels, it is necessary to unify the sampling time.