1. Pharmaceutical composition containing as active principles Vitamin D associated to a calcium salt characterized in that it comprises a binding agent chosen in the group consisting of: propylene glycol, a polyethylene glycol presenting a molecular weight comprised between 300 and 1500, liquid paraffin or silicone oil and that the Vitamin D is present at the rate of 1 - 2 g of calcium for 500 1000 I.U. of Vitamin D. 2. Pharmaceutical composition according to Claim 1, in which the calcium used is in the form of a salt chosen in the group consisting of: phosphate, glycerophosphate, carbonate, bicarbonate, lactate, citrate, tartrate, gluconate, and chloride. 3. Pharmaceutical composition according to Claims 1 and 2, in which the calcium salt is calcium phosphate. 4. Pharmaceutical composition according to Claim 3 wherein the calcium phosphate is 30 - 80% by weight calculated on the total composition. 5. Pharmaceutical composition according to Claim 1, in which the Vitamin D used is Vitamin D2 (or ergocalciferol), Vitamin D3 (or cholecalciferol), or one of their mixtures. 6. Pharmaceutical composition according to Claim 5, in which the vitamin used is Vitamin D3. 7. Pharmaceutical composition (bag) according to Claim 1, containing the propylene glycol or polyethylene glycol in a quantity comprised between 5-15% by weight calculated on the total composition. 8. Pharmaceutical composition (tablet) according to Claim 1, containing liquid paraffin or silicone oil. 9. Pharmaceutical composition according to Claim 7, characterized as follows: Tribasic calcium phosphate (corresponding to 1200 mg of Ca++) 3.100 g Cholecalciferol (Vit. D3) 100 000 IU/g (corresponding to 800 IU) 0,008 g Propylene glycol 0.800 g E110 0.002 g Colloidal silica 0.120 g Lemon flavouring 0.100 g Microcrystalline cellulose - MCC 0.200 g Sodium saccharin 0.015 g Anhydrous citric acid 0.165 g Sucrose monopalmitate 0.120 g Mannitol q.s. to 7.000 g 10. Pharmaceutical composition according to Claim 7, characterized as follows: Tribasic calcium phosphate (corresponding to 1200 mg of Ca++) 3.100 g Cholecalciferol (Vit. D3) 100 000 lU/g (corresponding to 800 IU) 0.008 g Polyethylene glycol 400 0.800 g E110 0.002 g Colloidal silica 0.120 g Lemon flavouring 0.100 g Microcrystalline cellulose - MCC 0.200 g Sodium saccharin 0.015 g Anhydrous citric acid 0.165 g Sucrose monopalmitate 0.120 g Mannitol q.s. to 7.000 g 11. Pharmaceutical composition according to Claim 8, characterized as follows: Tribasic calcium phosphate (corresponding to 1200 mg of Ca++) 3.100 g Cholecalciferol (Vit. D3) 100 000 IU/g (corresponding to 800 IU) 0.008 g Liquid paraffin 0.500 g Sodium carboxymethyl cellulose 0.050 g Sodium saccharin 0.015 g Orange flavouring 0.100 g Sorbitol q.s. to 4.400 g 12. Pharmaceutical composition according to Claim 8, characterized as follows: Tribasic calcium phosphate (corresponding to 1200 mg of Ca++) 3.100 g Cholecalciferol (Vit. D3) 100 000 IU/g (corresponding to 800 IU) 0.008 g Silicone oil 0.500 g Sodium carboxymethyl cellulose 0.050 g Sodium saccharin 0.015 g Orange flavouring 0.100 g Sorbitol q.s. to 4.400 g 13. Process for the preparation of a pharmaceutical composition according to Claims 9 or 10, characterized by the following steps: a) in a granulator turning at high speed, distribute the binding agent, consisting of propylene glycol or low-molecular-weight polyethylene glycols over the calcium salt; b) add the colloidal silica, approximately 25% of the mannite, the citric acid, and the sodium saccharin, and mix for the time required and at the appropriate speed; c) add the mixture, prepared separately, consisting of sucrose palmitate, a suspending agent, flavouring, colouring agent, the remaining part of the mannite, and the Vitamin D3, and mix together with the rest of the preparation; d) distribute the granulate thus obtained into bags. 14. Process for the preparation of a pharmaceutical composition according to Claims 11 or 12, characterized by the following steps: a) in a granulator turning at high speed, distribute the binding agent, consisting of liquid paraffin or silicone oil, over the calcium salt; b) add in order, to a mixture of colloidal silica, carboxymethyl cellulose and sodium saccharin previously sifted, the Vitamin D3 and the sorbitol, mixing thoroughly every time before a new ingredient is added, pour the mixture into the rotating granulator and mix for the required time and at the appropriate speed c) compress the granulate to the required weight to obtain the desired tablets. 15. Composition according to Claim 1, for use in the treatment of nutritional deficiency of calcium and Vitamin D in the elderly, to reduce the loss of bone tissue linked to age and to prevent femoral fractures and other non-vertebral fractures. 16. Composition according to Claim 1, for use in the prevention of osteoporosis induced by treatment with corticosteroids. 17. Method for the treatment of nutritional deficiency of calcium and Vitamin D in the elderly, to reduce the loss of bone tissue linked to age and to prevent femoral fractures and other non-vertebral fractures, in which therapeutically effective quantities of a composition according to Claim 15 are administered to the patient. 18. Method for the prevention of osteoporosis induced by treatment with corticosteroids comprising administering to the patient an effective quantities of a composition according to claim 16.