The Effect of Chymosin on the Intestinal Absorption of Calcium

Background:

Osteoporosis is a frequent disease. Allegedly, more than 500,000 Danes are diagnosed with osteoporosis and, in consequence, seems every year more than 20,000 fractures. A number of factors are known to increase the risk of osteoporosis, including a low daily intake of calcium.

Several clinical trials with calcium supplements for adults (with or without simultaneous supplementation of vitamin D) have shown an increase in bone mineral density (Bone Mineral Density, BMD) and reduction the risk of fractures. Similarly, several studies have shown that high milk intake during childhood and adolescence may increase bone mass and reduce the risk of fractures later in life.

Since an adequate calcium intake is important for bone turnover and the risk of developing osteoporosis, it is important to explore ways to better calcium influx. Several studies have documented that supplementation with calcium tablets are often associated with a poor compliance - people do not remember to take the tablets. It is therefore desirable to find methods that can increase the intake of the amount of calcium which occurs naturally in the diet.

Calcium consumed through dairy products must first be cleaved from the molecules which it is bound to before it can be absorbed. Various methods have been tried to optimizing the amount of calcium absorbed from dairy products, including the addition of so called fructo-oligosaccharides (FOSS) and casein phosphopeptides (CPPs).

Chymosin is an enzyme which cleaves the protein binding between some amino acids in κ-casein. The reaction occurs after ingestion of milk and causes a process whereby the time the milk is staying gastrointestinal tract is extended, this can lead to enhanced uptake of calcium. When the body's calcium balance is in balance the excretion in urine (24 h)is in roughly the size as the intake. Therefore a measurement of circadian urine excretion of calcium can determine the amount of calcium absorbed from the intestine.

Purpose and hypothesis:

Primarily the study intends to clarify whether the addition of chymosin to milk increases the intestinal calcium absorption. Secondary to explore issues of significance for this effect, including vitamin D status and amount of daily calcium intake, and whether a change in calcium absorption has immediate effects on bone turnover (measured as plasma osteocalcin, plasma bone specific alkaline phosphatase, and the renal excretion of cross-linked N-terminal telopeptide of type 1 collagen (NTx/Cr) ratio) and on the parathyroid function (measured as PTH). Finally we will explore relations between bone mineral density (BMD) and the measured parameters (in terms of P-PTH, P-25OHD, P-1,25(OH)2D, P-osteocalcin, P-BSAP, and U-NTx/Cr).

Design:

The study is conducted as a randomized double-blinded controlled cross-over trial in which 125 healthy subjects will be asked to drink a glass of milk with or without added chymosin at two occasions. The two time two test days will be separated by 10-18 days. Neither study participants nor the staff conducting the investigation (investigator) will while the trial will be conducted know on which day of the trial which milk contains chymosin (double-blinded). About chymosin added to milk on the first or second test day will be determined by lot (randomized study).

Study Population:

Healthy participants in the agegroup of 25-40 years old are recruited. From the central personal register (CPR register) a list of young people living in the Aarhus area is drawn up, followed by sending out a direct letter asking for participation in the study. At the same time a questionnaire will clarify whether participation is possible, i.e. whether the criteria for participation in the survey are meet.