Menstrual cycle lengths and bone mineral density: a cross-sectional, population-based study in rural Chinese women ages 30–49 years

Introduction The menstrual cycle involves periodic fluctuations in estrogen and progesterone levels. Longer cycles have been associated with longer follicular phase, delayed estrogen peak and a lower mean oestradiol level of the entire cycle. Methods We hypothesized that prolonged menstrual cycle length is associated with decreased bone mineral density (BMD) in a population of pre- and perimenopausal women. This population-based cross-sectional study was conducted in rural Anhui province, China. It includes 4,771 women, aged 30 to 49 years, who did not smoke or drink alcohol, and did not use oral contraceptives or breastfeed during the previous year. Dual-energy X-ray absorptionometry (DEXA) BMD measurements were taken at four skeletal sites: whole body, total hip, femoral neck and lumbar spine. Menstrual cycle characteristics (polymenorrhea, short normal, long normal, oligomenorrhea, 90-day amenorrhea, irregular cycle) in the prior year were assessed by questionnaire. Results Prolonged menstrual cycle was consistently associated with decreased BMD at whole body, total hip, and femoral neck in both age 30–39, and age 40–49 stratum (p_trend<0.05). Prolonged menstrual cycle was also associated with decreased lumbar spine BMD for women aged 40–49 (p_trend<0.05). Among women with normal cycles aged 30–39, menstrual cycle length in the previous year was inversely associated with whole-body BMD (p<0.05). Women with 90-day amenorrhea had significantly lower mean total hip and femoral neck BMD relative to women with short normal cycles in the 30–39 age group; and had significantly lower whole body and total hip BMD relative to short normal cycles in the 40–49 age group. BMD in poylmenorrheic women did not differ from BMD in women with short normal cycles at any of the skeletal sites. Conclusions We conclude that prolonged menstrual cycle length is associated with decreased BMD in pre- and perimenopausal women in this population.