Zurich Disability Prevention Trial

Inclusion criteria: * Age 70+ * Fall in the last 12 months before screening (with or without a fracture) * Living at home (community-dwelling) * Men or women * Mobile with or without walking aid - have to be able to use public transportation to attend the clinical visits at the trial centre * Score of at least 27 at the screening Folstein Mini Mental test + normal clock test * Patient understands the study procedures, alternative treatments available and risks involved with the study, and voluntarily agrees to participate by giving a written informed consents. * Patient meets the entry minimal requirements based on routine clinical laboratory safety screening tests and the Folstein mini mental status (score 27+ required) performed at the Screening Visit. * Patient is willing to perform all study tests, attend all required office visits, and provide blood and urine samples. Exclusion criteria: * Serum calcium adjusted for albumin of \> 2.6 nmol/l * Pathologic fracture in the last year (except for fractures due to osteoporosis) * Chemo therapy / Radiation due to cancer in the last year * Treatment which has an effect on bone metabolism (e.g. bisphosphonate, PTH, calcitonin, chronic cortisone intake \> XYmg/day for more than XY month/years (except for inhalation and sporadic infiltration)) * Oral vitamin D intake of more than 800 IU per day * Unwilling to stop calcium supplementation and vitamin D supplementation during the trial (maximal calcium supplement intake 250mg/d; no additional vitamin D supplementation) * Severe visual or hearing impairment * Unwilling or unable to take study medication * Diseases with a risk of recurrent falling (e.g. Parkinson's disease/syndrome, Hemiplegia after stroke, symptomatic stenosis of the spinal canal, polyneuropathy, epilepsy, recurring vertigo, recurring syncope) * BMI \>= 40 * Estimated creatinine clearance \< 15 ml/min (estimated Creatinine Clearance Cockcroft and Gault) * Malabsorption syndrome (celiac diseases, inflammatory bowl disease) * Diseases that may enhance serum calcium: sarcoidosis, lymphoma, primary hyperparathyroidism * kidney stone in the last 10 years * Abnormal indices of calcium metabolism, uncontrolled hypocalcemia. * Patient heavily consumes alcohol containing products defined as greater than (\>) 3 drinks (beer, wine, or distilled spirits) of alcoholic beverages per day. * Patient is unlikely to adhere to the study procedures, to keep appointments, or is planning to relocate during the study. * Patients who are planning a stay in a "sunny" location (e.g. winter sun resort) for more than two months per year * Medication which has an effect on 25-hydroxyvitamin D level (e.g. certain anticonvulsants (e.g. Phenobarbital, Carbamazepin, Phenytoin)) * M. Paget (Ostitis deformans) * inflammatory arthritis (e.g. rheumatoid arthritis, reiter syndrome, psoriasis arthritis)