1. A method for concurrently reducing the risk of both vertebral and non-vertebral bone fracture in a human subject at risk of having osteoporosis, comprising administering to the said subject a parathyroid hormone without concurrent administration of an antiresorptive agent other than vitamin D or calcium, in a daily dose from 20 mug till 40 mug. 2. Use of a parathyroid hormone consisting of amino acid sequence 1-34 of human parathyroid hormone for the manufacture of a medicament for concurrently reducing the risk of both vertebral and non-vertebral bone fracture in a woman during postmenopausal period at risk of or having osteoporosis, wherein said medicament is administered to said subject without concurrent administration of an antiresorptive agent other than vitamin D or calcium, in a daily dose from 20 mug till 40 mug for at least about 12 months up to 3 years. 3. The method of claim 2 wherein said daily dose is 20 mug. 4. The method of claim 2 wherein said daily dose is administered for at least about 24 months. 5. Use according to claim 2 wherein said medicament is contained within a packaging material, said packaging material comprising printed matter which indicates that said medicament is effective for concurrently reducing the risk of both vertebral and non-vertebral bone fracture in a woman during postmenopausal period at risk of having osteoporosis when administered to said subject such that said parathyroid hormone is administered without concurrent administration of an antiresorptive agent other than vitamin D or calcium, in a daily dose from 20 mug till 40 mug for at least about 12 months up to 3 years. 6. Use of a parathyroid hormone for the manufacture of a medicament for concurrently reducing the risk of both vertebral and non-vertebral bone fracture in a c human subject at risk of having osteoporosis, comprising administering to the said subject a parathyroid hormone without concurrent administration of an antiresorptive agent other than vitamin D or calcium, in a daily dose from 20 mug till 40 mug. 7. Use of a parathyroid hormone for manufacture of a medicament for strengthening cortical bone in a human subject at risk of having osteoporosis, wherein said medicament is administered to said subject without concurrent administration of an antiresorptive agent other than vitamin D or calcium, in a daily dose of 20 mug or 40 mug. 8. The method of claims 6 and 7 wherein said human subject is at risk of having osteoporosis arising from an age-related hypogonadal condition. 9. The method of claim 8 wherein said human subject is a postmenopausal woman. 10. The method of claims 2-9 wherein said human subject has osteoporosis. 11. The method according to claims 2-10 wherein said medicament is administered for at least about 12 months up to 3 years. 12. The method of claim 6 wherein said daily dose is 20 mug. 13. The method of claim 6 wherein said daily dose is administered for at least about 24 months. 14. Use according t claim 6 wherein said medicament is contained within a packaging material, said packaging material comprising printed matter which indicates that said medicament is effective for concurrently reducing the risk of both vertebral and non-vertebral bone fracture in a human subject at risk of or having osteoporosis when administered to said subject such that said parathyroid hormone is administered without concurrent administration of an antiresorptive agent other than vitamin D or calcium, in a daily dose of 20 mug or 40 mug. 15. The method of claims 6-14 wherein said parathyroid hormone is selected from PTH (1-31), PTH (1-34), PTH (1-38), PTH (1-41) and PTH (1-84). 16. The method of claim 15 wherein said parathyroid hormone represents PTH (1-34) of a human subject. 17. The method of claim 15 wherein said parathyroid hormone represents PTH (1-84) of a human subject.