Objectives: This review emphasizes results from population based studies in order to provide a reliable knowledge base and define major knowledge gaps for future research.
Methods: The review systematically addresses the following aspects of menopause research: definition of menopause and menopause transitions; age at natural menopause and at inception of perimenopause; factors affecting timing and length of menopause transitions; concurrent hormone, menstrual and vascular changes. Under each substantive heading, available reports of original research are reviewed, assessed for reliability and summarized with respect to their contribution to the knowledge base.
Results: From this review, the following reliable information can be summarized: median age at natural menopause in Caucasian women occurs between 50 and 51-55 years of age, is not affected by timing of surgical menopause and is affected by cigarette smoking, with current smokers having an earlier menopause by 1.5-2.0 years. No other factors appear to have an independent effect on age at menopause. There is no evidence of any secular trend in age at menopause. Evidence is accumulating that most physiological change associated with menopause either occurs or begins before the final menstrual period.
Conclusions: We lack reliable information on the following: estimates of age at menopause from non-industrialized countries and diverse ethnic groups; information on perimenopause; differing perceptions of menopause, cross culturally; multi-disciplinary prospective data that can link various processes into coherent patterns.