Endocrine characteristics of early menarche
Apter et al. (1989) reported that women aged 20-31 years who had had menarche before age 13 had lower serum concentrations of sex-hormone-binding globulin (SHBG) than women who had had menarche at ages 13 and above. This difference was evident in serum samples collected in both the follicular and the luteal phases of the cycle, but the difference was slightly larger in the follicular phase samples. Apter et al. also found that early menarche was characterized by high serum concentrations of oestradiol in the follicular phase, but not in the luteal phase. We too have noted a positive correlation between SHBG and age at menarche in adult women aged 34-55 years (Moore et al., 1987). The report of Apter et al. suggesting that some of the endocrine characteristics associated with early menarche m y be most marked during the follicular phase prompted us to re-examine our data to see whether the relationship between SHBG and age at menarche digered between the follicular and the luteal phases of the cycle.
The data presented here are ffom a cross-sectional analysis of 5,000 women on the Island of Guernsey. At recruitment, a blood sample was collected irrespective of the stage of the menstrual cycle, and the days of onset of menses preceding and following serum collection were recorded, along with recalled age at menarche, other risk factors for breast cancer and current use of exogenous sex hormones and other medicines. Data are reported here for all 1,859 women who were pre-menopausal and were not using drugs likely to aflect SHBG (Moore et al., 1987; Key et al., 1989). The serum SHBG concentration was measured by immunoradiometric assay (Hammond et al., 1985).
To obtain an approximately normal distribution, the square-root transformation of SHBG concentration was used in all calculations, but the mean values presented have been returned to the original units by squaring the computed mean values. All mean values presented have been adjusted by analysis of co-variance for age, body mass index (BMI), parity, previous use of oral contraceptives, and approximate duration of serum storage.
Figure 1 shows the mean values of SHBG during four 7-day stages of the menstrual cycle in women who had had menarche before age 13 (n = 679) and in women who had had menarche at ages 13 and older ( n = 1180). Mean SHBG was higher in samples collected during the second half of the cycle (approximate luteal phase) than in samples collected during the first half of the cycle (approximate follicular phase), but this increase in SHBG during the luteal phase was more marked in women who had had an early menarche than in those who had had a later menarche. Further statistical analyses were made with samples classified simply as follicular lfirst 2 weeks) or luteal (last 2 weeks). Within the follicular-phase samples, there was a statistically signifcant difference in mean SHBG between women who had had an early menarche and women who had had a later menarche (2-sided p = 0.003), but no such digerence was found among the luteal-phase samples (2-sided p = 0.793). Repeating these analyses with stage of cycle classified as days from the end of the menstrual cycle, rather than days from the beginning of the cycle, produced similar results.
Our results suggest that women with early menarche have lower SHBG during the follicular phase than women with later 75.1 --f Menarche ~12years + Menarche t3+ years 1-7 8-14 15-21 22+ Day of Menstrual Cycle