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Corresponding author at: Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, Queen's University, Victory 4, 76 Stuart St., Kingston, ON, K7L 2V7, Canada.
Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, Queen's University, Victory 4, 76 Stuart St., Kingston, ON, K7L 2V7, CanadaDepartment of Public Health Sciences, Queen’s University, Carruthers Hall 2nd Floor, 62 Fifth Field Company Lane, Kingston, ON, K7L 3N6, Canada
Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, Queen's University, Victory 4, 76 Stuart St., Kingston, ON, K7L 2V7, Canada
Center for Gerontology and Healthcare Research, Department of Health Services, Policy and Practice, School of Public Health, Brown University, 121 South Main Street, Providence, RI, 02903, USA
Physical functioning represents an integrated marker of healthy biological aging.
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Grip strength and gait speed are two validated measures of physical function.
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Age at natural menopause has been less studied than menopausal status as a factor that might relate to physical function.
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Our study found that an age at natural menopause of under 40 years is a risk factor for poor physical functioning.
Abstract
Objective
Grip strength and gait speed are objective measures of physical function, which in turn is an indicator of biological aging. We evaluate the association between age at natural menopause (ANM) and physical functioning in a sample of postmenopausal women drawn from the International Mobility in Aging Study (IMIAS).
Study Design
Retrospective cohort study of 775 women aged 65–74, from Albania, Brazil, Colombia and Canada, who had experienced natural menopause.
Main outcome measures
Gait speed and grip strength were obtained following standardized protocols. The association between self-reported ANM (<40, 40–44, 45–49, 50–54 and ≥55) and gait speed (m/s) and grip strength (kg) was assessed by linear regression analyses adjusting for several life-course economic and reproductive exposures, height, BMI and smoking.
Results
Overall, women with ANM ≥ 55 had higher gait speed than those with ANM 50–54 (β = 0.05; 95%CI: 0.01, 0.10). Women with ANM < 40 had significantly lower grip strength compared with all other groups (β= −2.58; 95%CI: −4.43, −0.74). In region-specific analyses, ANM was associated with grip strength in Albania and Latin America and with gait speed in Albania only. No associations were observed in Canada.
Conclusions
ANM is associated with markers of physical functioning. Differences across study sites suggest that women in socially disadvantaged areas may reach menopause with different physiological reserves than those from more advantaged settings, leading to greater losses in muscle strength in postmenopausal years. More work comparing distinct populations is needed to better understand the underlying mechanisms.
Physical functioning represents an integrated marker of healthy biological aging, capturing the interaction of a broad array of physiological systems [
A short physical performance battery assessing lower extremity function: association with self-reported disability and prediction of mortality and nursing home admission.
]. While both sexes experience functional losses with increasing chronological age, on average, women experience worse physical function and greater physical decline than men at similar ages [
]. The reasons for this disparity are poorly delineated, but one hypothesis centers on women’s unique life-course reproductive events, including age at natural menopause (ANM) [
Observational studies suggest that the transition to menopause is a specific time in which accelerated loss in muscle mass and strength among women occurs [
]. Gait speed at one’s usual pace is highly conserved until older adulthood and substantial changes in gait speed manifest only after a substantial reduction of fitness or nerve conduction velocity [
Compared to studies of the menopausal statuses, ANM has been less studied as a reproductive exposure in relation with physical function, and the results are not consistent. Among postmenopausal women, Tom et al. [
] observed that those who transitioned to menopause at later ages had faster walking speed than women who transitioned earlier. For instance, women with natural menopause at 50–54 ha d a walking speed 0.08 m/s faster than those who experienced menopause at <45 years. In contrast, an earlier study of a UK birth cohort showed that neither menopausal status nor age at menopause was associated to grip strength [
], which are risk factors for poor physical function. As we have previously reported, childhood social and economic disadvantages are associated with earlier menopause [
]; however, these factors have not been examined with a life-course perspective with regard to the association between ANM and physical functioning. By life-course perspective, we account for contemporary conditions and prior living circumstances when examining ANM in a cohort of senior women. Moreover, no studies have considered these effects across populations of diverse social backgrounds, and none in women from Latin America or Eastern Europe, despite calls from experts in population aging to conduct investigations of physical function in more ethnically diverse samples and to perform cross-national comparisons [
]. The present study aims to investigate the association of ANM with gait speed and grip strength using a life-course approach, in a socially diverse cohort of women from the International Mobility and Aging Study (IMIAS) [
], conducted in five sites in four countries: Tirana (Albania), Natal (Brazil), Manizales (Colombia), Kingston (Ontario, Canada), and Saint-Hyacinthe (Quebec, Canada). The IMIAS cohort was established in 2012 at which time participants were 65–74 years old. A detailed description of the recruitment and study procedures for the IMIAS can be obtained from Gomez et al. [
]. Institutional ethics review board approval was obtained from the participating sites. Written informed consent was obtained from all participants.
As part of the Short Physical Performance Battery (SPPB), a timed 3 or 4 m gait speed test was conducted twice and the fastest time was used for these analyses [
A short physical performance battery assessing lower extremity function: association with self-reported disability and prediction of mortality and nursing home admission.
A short physical performance battery assessing lower extremity function: association with self-reported disability and prediction of mortality and nursing home admission.
Grip strength was measured using a handheld dynamometer (Jamar Hydraulic Hand Dynamometer®). Participants were seated on a chair with no armrest and positioned to flex their elbow at 90°, shoulder adducted and neutrally rotated, and forearm in neutral position. They were asked to grip the handle as hard as they could with their dominant hand for 5 s. Three measurements were carried out, and the highest value was used in the analyses.
Age at natural menopause (ANM) was defined through the following question: 1) how old were you when you had your last menstrual period? Women whose last menstrual period was the result of a hysterectomy (with or without oophorectomy) were excluded. Categories of ANM were defined as: <40 (premature menopause), 40–44 (early menopause), 45–49, 50–54 and ≥55. Our reference age category was 50–54 years, based on results from Tom et al. [
] in which women in this age group had faster gait speed than those with a younger ANM.
The following characteristics were considered as potential covariates. Age, which was self-reported. Years of education, categorized into site-specific tertiles as follows: Tirana: <8, 8–12, ≥13; Manizales and Natal: <4, 4–5, ≥6; Kingston: <15, 15–17, ≥18; St Hyacinthe: <11, 11–12, ≥13. Income, classified into ‘poor’, ‘middle to middle high’, and ‘high’ also according to site-specific tertiles as follows: Tirana: annual income of <1000 USD, 1,000–2,000 USD, ≥ 2000 USD; Manizales and Natal: monthly income of <1 minimum salary, 1 minimum salary, ≥ 2 minimum salaries; and Canadian sites: annual income of <20,000 CAD, 20,000–40,000, >40,000. Height and BMI, measured and calculated following standard protocols. We categorized BMI into ‘underweight or normal weight’, ‘overweight’ and ‘obese’.
Hormone replacement therapy (HRT), categorized as those who never used HRT and those who had used HRT at some point in their lives. Post-menopausal hysterectomy (with or without oophorectomy), categorized as yes/no. Smoking status, categorized as current smokers or non(current)-smoker. Lastly, we considered four life-course variables; childhood social adversity and childhood economic adversity, lifetime parity and adolescent childbirth. Childhood social adversity encompassed experiences of parental alcohol or drug abuse, witnessing physical violence in the family, and/or physical abuse during childhood. Childhood economic adversity occurred if participants reported poor economic status, hunger, and/or unwanted parental unemployment. Both childhood adversity measures were based on a validation study previously carried out with data from IMIAS [
]. Parity was categorized into nulliparous, 1–3 children, 4 children or more. Adolescent childbirth was defined as giving birth before 20 years of age.
Descriptive analyses included comparison of the sample by outcomes, menopause-related characteristics and covariates using chi2 for categorical/dichotomous covariates, and one-way ANOVA for continuous variables. Linear regressions were performed to assess the relationships between ANM and physical function, as linearity diagnosis met criteria of normality and heteroscedasticity. Analysis was conducted with all sites together as well as separately by region: the Southeastern European site (Tirana, Albania), Latin American sites (Manizales, Colombia and Natal, Brazil), and Canadian sites (Kingston, Ontario and Saint-Hyacinthe, Quebec). Grouping by region increased the sample size for data analyses and interpretation. As we have previously demonstrated in IMIAS, cities in the same country and region may share similar contextual factors [
]. For the combined sites analysis, we increasingly adjusted for covariates in a total of six regression models: 1) age and study site, 2) years of education and income, 3) height and BMI; 4) hysterectomy and HRT, 5) smoking status, and 6) early life-course exposures. For the region-specific analysis, we used a backwards selection procedure to determine covariates relevant to the region and obtain the most parsimonious model [
]. Statistical analysis was conducted using STATA, version 14.
3. Results
Fig. 1 depicts the total number of participants included in our analyses. Mean ANM was 49.0 (SD 4.9) in Albania, 48.11 (SD 5.6) in Latin America, and 50.3 years (SD 5.19) in Canada, (p < 0.001). Table 1 shows the distribution of covariates by categories of ANM. For all sites combined, those in the lowest education tertile had earlier ages at menopause (p = 0.04), as did those who reported currently smoking (p = 0.02) and those who gave birth 4 or more times (p = 0.02). Taller women had later ANM (p = 0.01). Few differences were observed within regions (Supplemental tables A–C).
Fig. 1Flow diagram of participant inclusion for gait speed and grip strength analysis.
Table 2 shows differences in gait speed and grip strength by ANM and covariates. For all sites combined, a difference in gait speed was observed across categories of ANM, with women with an ANM of ≥55 having higher mean gait speed (0.97 m/s) compared to women with ANM 50–54 (0.89 m/s). Mean grip strength increased progressively with later ANM (Table 2) and a marked and significant difference was observed between women with ANM < 40 and the reference categories of 50–54, as well as ≥55 years. In region-specific analysis (Supplemental material, Table 2A and 2B), no differences in mean of gait speed or mean of grip strength were observed across categories of ANM. However, some pairwise analysis shows that in Albania, women with an ANM of ≥55 had higher gait speed compared to women with an ANM of 50–54 (0.94 m/s vs 0.81 m/s, p = 0.02). Similarly, women in Latin America with an ANM <40 had lower grip strength than those 50–54 (Supplemental material, Table 2B).
Table 2Distribution (or mean) of exposure variable and population characteristics by gait speed and grip strength.
In combined site analysis, gait speed was associated with education, income, height, BMI, HRT, childhood adversities, teen pregnancy and parity; grip strength was associated with age, height, HRT, childhood economic adversity, teen pregnancy and parity (Table 2). Women in Albania and Latin America had lower gait speed as well as grip strength compared to women in Canada (Supplemental tables 2A, B). Covariates associated with gait speed in all regions were age, education and income (Supplemental Table 2A). In addition, gait speed was associated with height, BMI, smoking and childhood social adversity in Canada, with height, BMI, HRT, and childhood economic adversity in Latin America and with childhood economic and social adversity in Albania (Supplemental Table 2A). In region-specific univariate analyses, height was associated with grip strength in all regions (Supplemental Table 2B). In addition, grip strength was associated with age, and smoking in Canada, with hysterectomy and HRT in Latin America, and with age, income, and childhood economic and social adversity in Albania (Supplemental Table 2B). In multivariable analyses, with sites combined ANM was associated to gait speed in all models (Table 3). Women with ANM ≥ 55 years had higher gait speed compared to 50–54 years, with no differences observed with the other ANM categories. In region-specific analysis (Supplemental Table 3A), Albanian women with ANM ≥ 55 years had a higher gait speed compared to 50–54 years (0.129 m/s, CI: 0.008-0.251). No association was observed in Latin America or Canada, where differences in gait speed between >55 vs 50–54 category were around 0.03 m/s (Supplemental Table 3A). In the grip strength analysis (Table 4), a borderline association was found in all multivariable models with ANM; with a difference of 2.6 kg observed between women with ANM < 40 compared to the reference group of ANM 50–54. In the region-specific analysis (Supplemental Table 4A), although only in Albania there were a significant effect of ANM on grip strength, women with ANM < 40 had a lower grip strength compared to the reference group of 50–54 years in all sites, 2.74 kg among Canadian women, 2.45 kg in Latin America women, and 5.55 kg, in Albanian women.
Table 3Multivariate linear regression models presenting the association of ANM and gait speed.
Our study suggests an association between ANM and physical functioning. In the case of gait speed, later ANM results in higher mean gait speed. For grip strength, the difference observed was more evident for women with premature menopause (ANM < 40) compared to older categories (i.e., women with ANM < 40 have a lower grip strength than women with older ANM). To our knowledge, this is the first study to apply a life-course perspective to examine the association between ANM and physical functioning. Our results suggest that the observed associations remain when additional social and economic exposures across the life-course are considered, suggesting that ANM may contribute independently to the physical functioning of older women.
Later transitions to menopause appear to favor better gait speed. This is consistent with Tom et al. [
], who observed differences in gait speed between those with ANM ≥ 55 as compared to ANM at earlier ages. In their case, lower gait speeds were observed in those with ANM < 45, while in our study the differences were significant for premature menopause (ANM < 40).
Our study is the first to show differences in the association of ANM and physical function by social context. Although caution should be applied when interpreting these finding due to the low proportion of women in some categories of ANM in individual study cites, they are valuable to further pursue. Differences in gait speed and grip strength by ANM categories were higher in Albanian women, than in the other sites. In Latin America and Canada the differences in grip strength were large (-2.45 Kg and -2.74 Kg respectively in women with ANM < 40) but not statistically significant probably due to the small number of women in this AMN category. Da Câmara et al. reported no association between menopause status and gait speed and a significant association with grip strength in Brazilian women [
]. Thus, we hypothesize that grip strength is a more sensitive physical measure of the impact of age at menopause in social contexts such as Latin America and Albania. It is possible that the greater overall early life adversity experienced by women in Latin America and Albania negatively affected muscle mass and strength across the life-course, especially if coupled with low lifetime physical activity [
]. In other words, women in these social contexts had less physical reserves going into older age. Thus, grip strength may be a sensitive indicator of functional decline in these populations of women, but less sensitive in a population of older Canadian adults who suffered less adversities during childhood, hence entering older ages in better overall health and greater physical strength.
The effects of HRT on muscle power and strength remain in debate. It is interesting to point out that in our study 60% of women with natural menopause in Canada, 16% in Latin American and only 4% in Albania ever received HRT. In the bivariate analysis, HRT was associated with higher gait speed, which is consistent with previous studies [
]; however, the effect of ANM was independent of HRT. A protective effect of long-term HRT on grip strength has been reported in middle age African American women [
We cannot rule out the survival effect in this cohort of women. Gait speeds of 1 m/s or higher are consistently associated with survival longer than expected based on age and sex alone. A gait speed of 0.8 m/s is associated with median predicted life-expectancy at most ages and for both sexes [
]. Mean gait speeds in Manizales and Natal are at or below these cut-off values. This suggests that most participants at these sites have progressed quite far in the disablement process, as indicated by slow gait speeds; and it is also possible that a survival bias is leaving women more resilient to negative consequences in the sample. Similarly, premature menopause is related to greater mortality [
], further raising the possibility of a more resilient sample of older women in our cohort.
This analysis has limitations. We only included women with natural menopause as the sample size for surgical menopause was small, and because information about type of oophorectomy (unilateral versus bilateral) was not available. A recent publication of data from a sample in Canada demonstrated an association between hysterectomy and frailty [
Frailty is inversely related to age at menopause and elevated in women who have had a hysterectomy: an analysis of the Canadian Longitudinal Study on Aging.
]. It is possible that the exclusion of women with previous hysterectomy yields underestimates in our measures of association. We have adjusted by (post-menopausal) hysterectomy, and our results remain unchanged. A major strength of this work is the IMIAS heterogeneous population of women from different social contexts with available information about early life exposures, and in whom physical function was assessed by physical assessments rather than by self-reported measures. We further included only postmenopausal women, decreasing the confounding effect of age in the estimations of the relationships between ANM and physical function.
5. Conclusions
Age at natural menopause, especially premature menopause (ANM < 40 years), is a risk factor for poor physical functioning in a diverse sample of women. Whether this association is due to social or biological factors or both, our study highlights the importance of incorporating strategies earlier in life to prevent women from entering menopause with low physiological reserve and to maintain physical function during menopause.
Contributors
Maria P. Velez was responsible for funding acquisition, conceptualization, and drafting of the manuscript.
Nicole Rosendaal was responsible for formal analysis and revision of the manuscript.
Beatriz Alvarado was responsible for funding acquisition, conceptualization, formal analysis, and revision of the manuscript.
Saionara da Câmara was responsible for revision of the manuscript.
Emanuelle Belanger was responsible for funding acquisition and revision of the manuscript.
Catherine Pirkle was responsible for funding acquisition, conceptualization, and revision of the manuscript.
Conflict of interest
The authors declare that they have no conflict of interest.
Funding
This work was supported by CIHR (Canadian Institute for Health Research) grant: ACD 151286.
Ethical approval
This study abided by the human rights code of ethics and guidelines. Institutional Ethics review board approval was obtained from the participating sites. Written informed consent was obtained from all participants. Ethical approval was obtained from Queen’s University (HSREB 6020804).
Provenance and peer review
This article has undergone peer review.
Research data (data sharing and collaboration)
There are no linked research data sets for this paper. Data will be made available on request to the IMIAS Data Sharing Committee via a standard application procedure.
Acknowledgements
We thank the entire IMIAS (International Mobility in Aging Study) research team and participants, without whom this study would never have been possible.
References
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A life-course approach to healthy ageing: maintaining physical capability.
A short physical performance battery assessing lower extremity function: association with self-reported disability and prediction of mortality and nursing home admission.
Frailty is inversely related to age at menopause and elevated in women who have had a hysterectomy: an analysis of the Canadian Longitudinal Study on Aging.
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