This creative method of sequentially pooling prevalence across studies provides comprehensive time series data that can accurately portray the natural history of vasomotor symptoms during the menopause transition. Among the women experiencing vasomotor symptoms, our data show a peak vasomotor symptom prevalence at 1 year after FMP, with 50% of women reporting symptoms after 4 years and 10% reporting symptoms as far as 12 years after FMP.
Our findings are consistent with other recent cohort studies that explored symptom prevalence. In one study of older postmenopausal women (mean age, 67 years), over 30% of women experienced vasomotor symptoms more than 3 years after FMP47
. Another longitudinal study suggested that women began experiencing vasomotor symptoms approximately 2 years before FMP and that symptoms tended to last for a median of 4 years2
. In that cohort, as many as 20% of women reported hot flashes for more than 5 years48
If the duration of vasomotor symptoms is approximately 4 years, as our findings suggest, the clinical implications are substantial. A longer symptom duration may affect treatment decisions and clinical guidelines. The risks of diseases that are either induced or averted by HT, as well as the continuation of symptoms that can impact women’s quality of life with premature discontinuation of HT49
, need to be carefully weighed in determining an individual’s risk:benefit profile from HT or non-hormonal treatments.
There are also implications for research examining vasomotor symptom duration. The studies that laid the foundation for the duration of vasomotor symptoms were not designed to measure symptom duration. Methodologically robust prospective, longitudinal studies that examine symptom duration are needed to better understand the natural history of menopause. Ideally, studies should begin observation before the onset of symptoms, continue until symptoms cease, and account for level of symptom severity and the use of symptom-modifying treatments. Prospective data acquisition is needed to minimize recall error. Moreover, research should also aim to identify risk factors for persistent vasomotor symptoms among menopausal women. Only one longitudinal, epidemiological study to date has investigated risk factors such as socioeconomic status, lifestyle behaviors, and physical and psychological health on the presence of vasomotor symptoms26,50,51
, and found that menopausal status was the most consistent predictor of the presence of symptoms.
Although the STRAW criteria have helped to standardize nomenclature around the menopause transition, its broad categorization of time intervals, especially for late postmenopause, makes it less useful in determining the duration of symptoms. Further refinement of later postmenopause, using smaller incremental time intervals, would help characterize the duration of menopausal symptoms.
Limitations Our findings should be interpreted with caution because of the difficulties in translating symptom prevalence data into estimates of symptom duration. Symptom prevalence data do not allow us to determine when individual women started experiencing symptoms or when their symptoms abated. Simulation techniques could be used to estimate duration from prevalence data, but such analyses are beyond the scope of the present paper.
Additionally, many of the studies were cross-sectional and may have been subject to sampling variability. Although we excluded studies that were clinic-based to minimize the selection of more symptomatic women (selection bias), longitudinal studies with longer periods of follow-up would provide better estimates of the time course for symptom onset, prevalence, and severity of vasomotor symptoms over time.
Our estimates should be interpreted cautiously because the studies included in our analyses artificially truncated symptoms due to limited follow-up periods; that is, symptoms may have begun before the study began and may have extended beyond the length of the study.
Differences in the minimum level of symptom severity among studies could result in an underestimation of symptom prevalence. However, while studies reporting only women who had moderate, severe, or bothersome symptoms had lower symptom prevalence rates than studies that reported women experiencing any level of symptom severity, the patterns observed were similar across all groups.
Some studies excluded women who were taking HT, which could introduce a selection bias that would underestimate both the duration and severity of symptoms, as HT users likely had more severe baseline symptoms and obtained symptom relief while on HT. We were not able to stratify our analyses according to HT use because there were not enough studies excluding HT users.
Differing selection and retention rates in the studies included in our analysis could have affected our results. Those who participated or remained in a study for longer periods of time might have experienced more severe or longer duration of symptoms. Nonetheless, temporal patterns observed across diverse studies were remarkably consistent, suggesting that this selection and retention bias was either consistent across all studies or relatively insignificant.
Although our analyses included studies conducted in multiple countries, it may not be generalizable to non-white women. Only one study26
in our analyses included ethnically diverse participants. There is some evidence to show that vasomotor symptom reporting differs across ethnic groups52
. However, to our knowledge, there is no evidence to show that vasomotor symptom duration differs by ethnicity.
In conclusion, these results suggest that the vasomotor symptoms of menopause may last longer than 2 years, and for a median of about 4 years. The data should lead to reevaluating the course of treatment of menopausal symptoms given the risks and benefits of longer-term use of HT. Further prospective, longitudinal studies of menopausal symptoms that account for the presence of symptoms before and after the observation period, the use of symptom-modulating treatments, such as HT, symptom severity, and ethnicity should be conducted to confirm these results. Studies should also assess potential risk factors for persistent vasomotor symptoms and typical age of onset of these symptoms.