Long-term effects of progestins on bone quality and fractures

Effect of progestogen-only contraception on premenopausal fracture risk: a case-control study

Our study demonstrated that progestogen-only oral and intrauterine contraceptives are not associated with fracture risk independent from age.

PURPOSE

The use of progestogen-only contraception, resulting in a hypoestrogenic state, has been associated with impaired bone acquisition and increased fracture risk. The aim of this large population-based study was to assess the fracture risk in association with the use of progestogen-only contraceptives (progestogen-only pills (POPs) and progestogen-containing IUDs (LNG-IUD)).

METHODS

We identified 14,421 women between 16 and 55 years of age with a first-time diagnosis of fracture and matched them with 14,421 random controls using the Disease Analyzer Database.

RESULTS

The results of the first adjusted logistic regression model (ever use vs. never use of progestogen-only contraceptives) revealed that there was no significant association between the use of POPs (OR = 0.98, 95% CI 0.90-1.07, p = 0.657) or LNG-IUDs (OR = 0.99, 95% CI 0.81-1.21, p = 0.945) and fracture incidence. Also, in the second regression model, we observed no effect of duration of use of POPs (OR = 1.01, 95% CI 0.98-1.03, p = 0.672) or LNG-IUDs (OR = 0.94, 95% CI 0.87-1.02, p = 0.177) on fracture occurrence. We also observed no effect in different age groups.

CONCLUSION

Our study results indicate that progestogen-only contraception (either POPs or LNG-IUPs) is not associated with fracture risk and may be considered a bone-safe option for adults and adolescents.

Bone health in estrogen-free contraception

Estrogens and progestogens influence the bone. The major physiological effect of estrogen is the inhibition of bone resorption whereas progestogens exert activity through binding to specific progesterone receptors. New estrogen-free contraceptive and its possible implication on bone turnover are discussed in this review. Insufficient bone acquisition during development and/or accelerated bone loss after attainment of peak bone mass (PBM) are 2 processes that may predispose to fragility fractures in later life. The relative importance of bone acquisition during growth versus bone loss during adulthood for fracture risk has been explored by examining the variability of areal bone mineral density (BMD) (aBMD) values in relation to age. Bone mass acquired at the end of the growth period appears to be more important than bone loss occurring during adult life. The major physiological effect of estrogen is the inhibition of bone resorption. When estrogen transcription possesses binds to the receptors, various genes are activated, and a variety modified. Interleukin 6 (IL-6) stimulates bone resorption, and estrogen blocks osteoblast synthesis of IL-6. Estrogen may also antagonize the IL-6 receptors. Additionally, estrogen inhibits bone resorption by inducing small but cumulative changes in multiple estrogen-dependent regulatory factors including TNF-α and the OPG/RANKL/RANK system. Review on existing data including information about new estrogen-free contraceptives. All progestins exert activity through binding to specific progesterone receptors; hereby, three different groups of progestins exist: pregnanes, gonanes, and estranges. Progestins also comprise specific glucocorticoid, androgen, or mineralocorticoid receptor interactions. Anabolic action of a progestogen may be affected via androgenic, anti-androgenic, or synadrogenic activity. The C 19 nortestosterone class of progestogens is known to bind with more affinity to androgen receptors than the C21 progestins. This article reviews the effect of estrogens and progestogens on bone and presents new data of the currently approved drospirenone-only pill. The use of progestin-only contraceptives leading to an estradiol level between 30 and 50 pg/ml does not seem to lead to an accelerate bone loss.

Clinical relevance in present day hormonal contraception

The contraceptive pill is an effective and very safe method to control pregnancies. It was developed 60 years ago, and despite that the composition has been the same since it was first developed (estrogen and progestogen), over the years the concentration of ethinyl estradiol has been reduced to improve tolerability. Nevertheless, progestogens are the basic active agent of hormonal contraception. The mechanism of progestogens is a multimodal one and basically three modes of contraceptive action can be distinguished: (a) A strong antigonadotrophic action leading to the inhibition of ovulation. The necessary dosage of ovulation inhibition per day is a fixed dosage that is intrinsic to each progestogen and independent of the dosage of estrogen used or the partial activities of the progestogen or the mode of application. (b) Thickening of the cervical mucus to inhibit sperm penetration and (c) desynchronization of the endometrial changes necessary for implantation. The on the market available progestogens used for contraception are either used in combined hormonal contraceptives (in tablets, patches or vaginal rings) or as progestogen only contraceptives. Progestogen only contraceptives are available as daily oral preparations, monthly injections, implants (2-3 years) and intrauterine systems (IUS). Even the long-acting progestogens are highly effective in typical use and have a very low risk profile. According to their introduction into the market, progestogens in combined hormonal contraceptives, have been described as 1st, 2nd, 3rd and 4th generation progestogens. The different structures of progestogens are derivatives from testosterone, progesterone and spironolactone. These differences in the molecular structure determine pharmacodynamic and pharmacokinetic differential effects which contribute to the tolerability and additional beneficial or therapeutic effects whether used in combined oral contraceptive (COC) or as progestogen only drugs. These differences enhance the individual options for different patient profiles. The new development of polymers for vaginal rings allowed on the one hand, the improvement of the estrogen/progestogen combination in these rings especially regarding the comfort of use for women (e.g. avoiding the use of cold chains or packages with up to 6-month rings) and on the other hand, the development of progestogen only formulations. Another future development will be the introduction of new progestogen only pills that will provide effective contraceptive protection with more favorable bleeding patterns and a maintenance of ovulation inhibition after scheduled 24-h delays in pill intake than the existing progestogen only pill (POP) with desogestrel (DES).

The clinical relevance of progestogens in hormonal contraception: Present status and future developments

The contraceptive pill is an effective and very safe method to control pregnancies. It was developed 60 years ago, and despite, that the composition has been the same since it was first developed (estrogen and progestogen), along the years the concentration of ethinyl estradiol has been reduced to improve tolerability. Nevertheless, progestogens are the basic active agent of hormonal contraception. The mechanism of progestogens is a multimodal one and basically three modes of contraceptive action can be distinguished: (a) A strong antigonadotrophic action leading to the inhibition of ovulation. The necessary dosage of ovulation inhibition per day is a fixed dosage that is inherent to each progestogen and independent of the dosage of estrogen used or the partial activities of the progestogen or the mode of application. (b) Thickening of the cervical mucus to inhibit sperm penetration and (c) Desynchronization of the endometrial changes necessary for implantation. The on the market available progestogens used for contraception are either used in combined hormonal contraceptives (in tablets, patches, or vaginal rings) or as progestogen only contraceptives. Progestogen only contraceptives are available as daily oral preparations, monthly injections, implants (2-3 years), and Intrauterine Systems (IUS). Even the long acting progestogens are highly effective in typical use and have a very low risk profile, with few contraindications. According to their introduction into the market progestogens, in combined hormonal contraceptives, have been described as first, second, third and fourth generation progestogens. Also, progestogens can be derived from testosterone, progesterone, and spironolactone that determine pharmacodynamic and pharmacokinetic differential effects. These effects contribute to the tolerability and additional beneficial or therapeutic effects whether used in combined oral contraceptives COC or as progestogen only drugs enhancing the individual options for different patient profiles. The new development of polymers for vaginal rings allowed on one side the improvement of the estrogen/progestogen combination in these rings especially regarding the comfort of use for women (avoiding of cold chain use or packages with up to six-month rings e.g.) and on the other side the development of progestogen only formulations. Another future development will be the introduction of new progestogen only pills that will provide effective contraceptive protection with more favourable bleeding patterns and a maintenance of ovulation inhibition after scheduled 24-h delays in pill intake than the existing pop with desogestrel.

Long-term progestin-only contraception in humans versus animal models

Abnormal uterine bleeding is the leading indication for discontinuation of long-term progestin-only contraceptives. Histological sections of endometria from long-term progestin-treated patients display abnormally enlarged blood vessels that are prone to bleed in a nonuniform manner. Because it has been complex to attain patients willing to complete long-term studies, and good quality endometrial tissues have proven difficult to obtain, animal models have been used to obviate this problem. In this review, we describe these models including the guinea pig, an animal model we have previously investigated, to assess the mechanisms involved in abnormal uterine bleeding following long-term progestin-only contraception.