Abstract
Many people are living under conditions of disturbed circadian rhythm, and this affects their nutritional state and health. The purpose of this study was to clarify the types and levels of minerals that need to be consumed in order to maintain and promote good health under conditions of disturbed circadian rhythm. Mineral balance is affected by many nutritional factors, but the interactions involved are not clear. Therefore, in this experiment, the effects of dietary mineral levels on calcium (Ca) balance were examined by an orthogonal array method, one type of investigation design which is superior for factorial analysis and factor interaction analysis. Calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na) and zinc (Zn) were selected as the factors, and eight kinds of diet were prepared on the basis of the L8 (27)-type orthogonal array. The dietary level of each mineral was normal (AIN-76) or 1/3.5 of the normal content. Four-week-old rats (Fischer 344 strain) were kept for 4 weeks and fed one of these diets. Continuous darkness was used as a model of disturbed circadian rhythm. Retention of Ca was determined by a balance test conducted on the last 3 days of the 4-week feeding period. The highest Ca absorption (%) was observed in rats fed the normal Mg, low Ca and P diet or the normal Na, low Ca diet, whereas the lowest was observed in rats fed the normal Ca, P and Mg diet or the normal Ca and Na diet. Ca absorption was affected by interactions between P and Mg, and between Ca and Na. The highest Ca retention (mg/day) was observed in rats fed the normal Ca diet, whereas the lowest was observed in rats fed the low Ca diet. These findings differ from the results obtained for rats kept exposed to a normal light and dark cycle, suggesting that changes in mineral metabolism occur in rats kept under constant darkness.
