Nutritional interrelationships between calcium, phosphorus and lactose in rats
Schaafsma, G.; Visser, R.
Journal of Nutrition 110(6): 1101-1111
1980
ISSN/ISBN: 0022-3166 PMID: 7381583 Document Number: 166897
From 3 months old, 6 groups each of 6 rats were fed on one of 3 types of diet with 15% lactose or glucose. The diets used were a control diet containing 0.6% calcium and 0.45% phosphorus and two high-P (1.3%) diets with normal (0.6%) or low (0.2%) Ca content. Whereas Ca retention and femur mass seemed to be unaffected, the high-P diets resulted in significant biochemical changes including: decreased plasma P almost throughout the whole of the study; increased plasma alkaline phosphatase and urinary total hydroxyproline after 17 and 42 weeks; nephrocalcinosis; depressed urinary Ca, and reduced femur density. With the excretion of nephrocalcinosis and depressed urinary Ca, these changes were more remarkable when the Ca content of the diet was low than when it was normal, and this difference was associated with a significant inhibiting effect of dietary Ca on the intestinal absorption and urinary excretion of P. Although lactose, compared with glucose, significantly improved the intestinal absorption and retention of Ca during bodyweight gain, which was reflected by an increased femur mass after 42 weeks, this sugar did not reduce the detrimental effects on bone and soft tissue resulting from the high-P diets. The findings, in line with the induction of nutritional secondary hyperparathyroidism and increased bone turnover in rats on high-P diets, indicate that lactose-stimulated Ca absorption will not prevent or diminish the biochemical changes associated with this disease; the results also stress the significance of the Ca content of the diet as a factor which may protect the body against excessive dietary P.