<qa>  How many patients will be included in the study?2. Study Design The study is a prospective, randomized cross-over study. Fifty patients will be included. All participants are randomly allocated to either group 1 or group 2. Each group consists of 25 patients. Group 1 patients receive alendronate 70 mg once weekly since the first week till the 16th week of the study, while group 2 patients receive the same dose of drug every week since the 17th week till the 32nd week. Group 1 patients will not receive alendronate since the 17th week till the 32nd week, and group 2 patients will not receive alendronate since the first week till the 16 week. The extent of coronary artery and aortic calcification is evaluated by using multi-detector spiral computed tomography, whereas bone mineral density is measured by dual-energy X-ray absorptiometry. Both examinations are performed at week 0, 16 and 32 for each participant. Serum level of calcium should be kept within normal limits and serum level of phosphorus should be kept below 6 mgdl. 