The relationship of menstrual cycle length status on bone mineral density in women from Tecumseh, Michigan.

Abstract

Background. Hypoestrogenemia of menopause is associated with low bone mineral density (BMD) and increased fracture risk. In addition, premenopausal women with low estrogen levels have decreased BMD and may be at increased risk for fracture, especially as they transition to menopause. Thus, hypoestrogenemia appears to be associated with decreased BMD pre- and postmenopausally. Menstrual cycle length status may reflect endogenous estrogen levels that could be associated with lower BMD. The study's purpose was to determine the relationship between BMD and menstrual cycle length status. It was hypothesized certain menstrual cycle length categories would be surrogate markers of marginal hormone status and would have lower bone mass. Research Design. A secondary data analysis using menstrual cycle calendar data collected between 1992-1993 and bone density measurements obtained in 1992 and 1993. Menstrual cycle length status was assessed four ways: (1) Clinical definitions of eumenorrhea, polymenorrhea, and oligomenorrhea, (2) Operational definitions of standard (within $\pm$ 2 SDs) or non-standard cycle length, (3) Number and proportion of cycles considered normal length (25-35 days), and (4) Range of cycle length for each subject (longest cycle - shortest cycle). Results. A total of 583 women were eligible from the Michigan Bone Health Study. Of these, a total of 441 women, 24-50 years of age, reported 4411 evaluable menstrual cycles during the 1-year interval covered in this study. No significant BMD differences were found between the clinically-defined, or operationally-defined groups. Analyses of the number or proportion of normal cycles and range of cycle length were not significant. Adjusting for age, body mass index, body fat (kg), or body lean mass (kg) did not significantly change the findings of an overall lack of association between menstrual cycle length status and BMD. Conclusion. Menstrual cycle length status was not associated with BMD in a population of premenopausal women. Hormone profiles of subjects with differing menstrual cycle length status will aid in defining contributors to the status groups and potential effects on BMD.