1. A method for treating physical conditions resulting from postmenopausal estrogen decline in a postmenopausal subject, said method comprising administering to said subject, an amount of estrogen sufficient to provide estrogen level in serum equivalent to a serum estradiol level of about 5-15 pg/ml. which is effective to produce a serum estradiol level in said subject of between about 5 pg/ml and about 15 pg/ml. 2. The method according to Claim 1, wherein said physical conditions are selected from the group consisting of postmenopausal estrogen decline, increased risk of osteoporotic bone fracture resulting from postmenopausal osteoporosis and loss of bone mineral density. 3. The method according to Claim 1 wherein said amount of estrogen which is administered is effective to produce a serum estradiol level in said subject of between about 5 pg/ml and about 10 pg/ml. 4. The method according to Claim 1, wherein said estrogen is estradiol. 5. The method according to Claim 4, comprising parenterally administering said amount of estradiol. 6. The method according to Claim 5, comprising administering not more than about 0,5 mkg of estradiol per day. 7. The method according to Claim 5, comprising administering between about 0,10-0,25 mkg of estradiol per day. 8. The method according to Claim 4, wherein estradiol is administered transdermally. 9. The method according to Claim 8, comprising administering not more than about 20 mkg of estradiol per day. 10. The method according to Claim 8, comprising administering 5-15 mkg of estradiol per day. 11. The method according to Claim 8, comprising administering about 10 mkg of estradiol per day. 12. The method according to Claim 4, wherein estradiol is administered transdermally. 13. The method according to Claim 12, comprising transdermally administering not more about 15 mkg of estradiol per day. 14. The method according to Claim 12, comprising transdermally administering about 5-15 mkg of estradiol per day. 15. A method for treating physical conditions in a postmenopausal subject, said method comprising transdermally administering less than about 20 mkg of estrogen per day to said subject, in the substantial absence of exogenous progestin, an amount of estrogen which is effective to produce a serum estradiol level in said subject of between about 5 pg/ml and about 15 pg/ml. 16. The method according to Claim 15, wherein said physical conditions are selected from the group consisting of postmenopausal estrogen decline, increased risk of osteoporotic bone fracture resulting from postmenopausal osteoporosis and loss of bone mineral density. 17. The method according to Claim 15, wherein said administration is prior to hysterectomy of said subject. 18. The method according to Claim 15, wherein said estrogen is estradiol. 19. The method according to Claim 18, further comprising the step of testing the serum estradiol level of the subject and determining that the serum estradiol level of the subject to be treated is normal for postmenopausal women in the same age group as the subject. 20. The method according to Claim 18, comprising administering 5-15 mkg of estradiol per day. 21. The method according to Claim 18, comprising administering about 10 mkg of estradiol per day. 22. A kit for use by a consumer afflicted with or susceptible to physical conditions resulting from postmenopausal estrogen decline, said kit comprising: a) a transdermal patch for administering estrogen in an amount sufficient to provide estrogen level in serum equivalent to a serum estradiol level in said subject of between about 5 pg/ml and about 15 pg/ml; and b) instructions describing a method of using the transdermal patch for treating physical conditions resulting to reduce the risk of osteoporotic bone fracture in said consumer.