This study aims to: 1) quantitatively assess parameters of bone calcium balance in healthy postmenopausal Asian women of Chinese descent; 2) assess possible ethnic differences in calcium metabolism by direct comparison of acquired data in Chinese postmenopausal women with those acquired earlier in Caucasian postmenopausal women using the same methodology; 3) assess differences in calcium and strontium metabolism in parallel to evaluate if strontium stable isotopes can be used for tracing bone calcium metabolism qualitatively

The study will follow closely the protocol that was used previously by the PI at ETH Zurich to study calcium metabolism in healthy postmenopausal women. Calcium metabolism will be studied after a single oral administration of a calcium tracer (Ca-41) and by following the excretion of the tracer in urine over 6 months. Obtained data will be used to assess parameters of calcium metabolism (flux rates and sizes of body calcium compartments) by kinetic modelling. A strontium tracer (Sr-84) will be administered in parallel and its urinary excretion pattern compared to Ca-41 excretion to determine if strontium tracers can be used to assess calcium metabolism qualitatively. Subjects will be supplemented with Vit D throughout the study. Vit D supplementation will commence 1 month before isotope administration.

Inclusion Criteria:

1. Last menstrual bleeding was at least 5 years ago.
2. Between the ages of 50 and 75 years old.
3. Both parents and 4 grandparents are/were of Chinese descent. It is not a necessity for the participant, participant's parents and grandparent's to be born and raised in Singapore to participate in this study.
4. BMI above 16 and below 30

Exclusion Criteria:

1. Diagnosed with osteoporosis
2. Presence of significant liver disease, malignancy (excluding myeloma in the study group), malabsorption syndrome, hypoparathyroidism, hyperparathyroidism, sarcoidosis or hyperthyroidism (from toxic multinodular goitre or Graves disease), Paget's disease osteosarcoma, acromegaly, Cushing's syndrome, hypopituitarism, diabetes mellitus or severe chronic obstructive pulmonary disease.
3. Current smoking and an alcohol intake exceeding one standard drink per day
4. Undergoing treatment with any of the following drugs (within the last 12 months) i) adrenocorticoid steroids (3 months or longer at anytime or >10 days of treatment within the previous 12 months) ii) anticonvulsant therapy iii) pharmacological doses of thyroid hormone (causing decline of TSH below normal) iv) bisphosphonates v) calcitonin vi) synthetic parathyroid hormone vii) selective estrogen receptor modulators viii) strontium ranelate ix) estrogen therapy x ) chemotherapeutic agents xi) sodium fluoride (any history of treatment with fluoride) xii) medications known to affect calcium metabolism (diuretics, antacids, calcium channel blockers etc.).
5. Presence of any other chronic illnesses.
6. Any other significant medical, psychiatric and/or social issue as determined by the investigator that would compromise subject's safety and/or compliance with trial procedure.
7. Any other clinically significant screening laboratory abnormality (as determined by the investigators).