The present study aims to develop a technique based on a single dose of a calcium isotope, which enables to determine the effect of a nutritional intervention on bone calcium metabolism. For this purpose nutritional interventions with calcium, vitamin D and vitamin K will be applied in postmenopausal women. Treatment effects will be determined by the urinary excretion of the calcium isotope and related to classical bone markers.

In the present proposal a method is described that may enable studying the effect of nutrition on bone calcium turnover far more accurate, within a shorter time frame and therefore less intensive for the volunteers in clinical studies as compared to presently existing methods. This method will enable screening for promising food concepts for combating osteoporosis within a relatively short time. Recent developments show that use of the nuclide 41Calcium (41Ca) and measurement by accelerator mass spectrometry (AMS) has great potential in measuring effects on bone level within a relatively short period of time. When introducing a diet change (intervention) the bone metabolism of calcium may change resulting in a changed 41Ca-signal in the urine. So far a few medication studies with osteoporotic volunteers have been performed and it appears that this ultrahigh sensitive technique may also be applicable for nutrition studies in healthy volunteers.

Inclusion Criteria:

1. Healthy as assessed by the

   • health and lifestyle questionnaire,
   • physical examination
   • results of the pre-study laboratory tests

2. Females aged 50-68 years at Day 01 of the study

3. Relatively low calcium intake as assessed by dairy intake questionnaire

4. Body Mass Index (BMI) < 30 kg/m2

5. Postmenopausal as confirmed by Follicle stimulating hormone (FSH) and oestradiol (E2) blood levels (FSH > 40IU/L, E2 < 70 pg/mL)

6. Normal Dutch eating habits

7. Voluntary participation

8. Having given written informed consent

9. Willing to comply with the study procedures

10. Appropriate veins for blood sampling/cannula insertion according to TNO

11. Willing to accept use of all nameless data, including publication, and the confidential use and storage of all data for at least 15 years

12. Willing to accept the disclosure of the financial benefit of participation in the study to the authorities concerned.

Exclusion Criteria:

1. Participation in any clinical trial including blood sampling and/or administration of substances up to 90 days before Day 01 of this study
2. Participation in any non-invasive clinical trial up to 30 days before Day 01 of this study, including no blood sampling and/or oral, intravenous, inhalatory administration of substances
3. Having a history of medical or surgical events that may significantly affect the study outcome, including cardiovascular disease or hypertension and gastrointestinal disease
4. Prescribed medication, including hormone replacement therapy (within 6 months before start of the study) and anticoagulant medication.
5. Reported intolerance for dairy products
6. Not willing to stop the use of Boerenkarnemelk and cheese of the following Dutch brands: Emmenthaler, Gruyere, Leer/Maasdammer
7. Alcohol consumption > 21 units/week
8. Not willing to stop use of supplements containing minerals or vitamins
9. Reported unexplained weight loss or gain of > 2 kg in the month prior to the pre-study screening
10. Reported slimming or medically prescribed diet
11. Reported vegan, vegetarian or macrobiotic
12. Recent blood donation (<1 month prior to the start of the study)
13. Not willing to give up blood donation during the study.
14. Personnel of TNO Quality of Life, their partner and their first and second degree relatives
15. Not having a general practitioner
16. Not willing to accept information-transfer concerning participation in the study, or information regarding her health, like laboratory results, findings at anamnesis or physical examination and eventual adverse events to and from her general practitioner.