Abstract and Introduction
The long-acting progestogen injectable contraceptives depot medroxyprogesterone acetate and norethisterone enanthate have been found to adversely affect bone mineral density in adult premenopausal women and adolescents. The effect of combined oral contraceptives on bone mineral density is variable, with no effect reported in premenopausal women; however, growing evidence suggests that low-dose combined oral contraceptives may be detrimental to bone mineral density in adolescents and young women. Much less information is available on other hormonal methods. Concerns regarding bone loss in depot medroxyprogesterone acetate users resulted in a US FDA black-box warning for this method. No restriction has been placed on the use of other progestogen-only or combined oral contraceptive methods. There are now concerns that these recommendations should be reviewed as new information emerges regarding low-dose combined oral contraceptives and evidence grows that supports recovery of bone mineral density postdiscontinuation of depot medroxyprogesterone acetate. There is a need to balance loss of bone mineral density with the benefit of effective contraception, especially in adolescents.
Bone mass increases rapidly from birth, and during adolescence women will gain 40–50% of their skeletal mass. Up to 90% of total adult bone content will be accumulated by the age of 20 years. Bone mineral density (BMD) remains fairly stable in adult premenopausal women, followed by bone loss over and above age-related loss in association with the menopause. It is important to know what factors affect peak bone mass in young women and bone loss in older women, as these are the chief determinants of a woman's susceptibility to osteoporosis.
Bone mineral density is one way of measuring bone strength. A BMD test measures how many grams of calcium and other bone minerals are packed into a segment of bone. The WHO has developed a classification system that uses the population mean as a reference against which a BMD measurement can be compared. A BMD measurement can be reported as a T-score and is expressed in standard deviations (SDs) from the normal population mean. In many studies a Z-score is reported, which is the difference in SDs between the BMD in users of a hormonal contraceptive method and nonuser controls in the same age group. The definition of normal BMD is no more than 1 SD below the young adult normal value. Low bone mass (osteopenia) is defined as 1–2.5 SDs below the population mean, and below this level osteoporosis is diagnosed.
Hormonal status, including reproductive hormones, are known to affect peak bone mass and bone maintenance. The relationship between estrogen deficiency and bone loss clearly suggests that hormonal contraceptive use may affect BMD. The noncontraceptive benefits of higher dose estrogen and progestin combined oral contraceptives (COCs) have included treatment of hypoestrogenic conditions in women where BMD is affected. Conversely, concerns have been raised regarding progestogen-only contraceptives, as the absence of estrogens from these methods and the resulting hypoestrogenic effect could lead to suppression of bone mass acquisition. In particular, concern is greatest in the age groups where BMD is in transition; younger women who have yet to reach peak bone mass and older women entering perimenopause and menopause where age-related bone loss has commenced.
Expert Rev of Obstet Gynecol. 2011;6(3):305-319. © 2011 Expert Reviews Ltd.
Cite this: Hormonal Contraception and Bone Mineral Density - Medscape - May 01, 2011.