Introduction

Menarche marks the final stage of puberty and the onset of a woman’s reproductive age1. The average age of menarche has decreased over the last century, though the extent of this decline and its causes are debated2. In low- and middle-income countries, the decline is occurring more rapidly than in high-income countries, likely due to improved socio-economic conditions and better nutrition3. A comparison of two generations of women in Tehran showed that daughters experienced menarche at a younger age than their mothers1. A national study spanning two health and disease plans over nine years examined trends in the age of menarche among individuals born over the last 50 years. The average age of first menstruation in 1980 was 13.86 ± 1.51 years, compared to 13.65 ± 1.47 years in 1999. In both periods, the age at menarche was significantly lower (p < 0.001) in urban areas than in rural areas. After nine years, the average age of first menstruation decreased significantly (p < 0.001) to 13.61 years in urban areas (from 13.76) and 13.72 years in rural areas (from 14.03)4. In 2014, a meta-analysis of 44 studies found that the average age at menarche for Iranian girls was 12.81 years5.

Menopause marks the end of a woman’s reproductive age, defined as the cessation of menstrual cycles due to the decline in ovarian follicle activity6. Menopause is defined as the absence of menstrual cycles for at least 12 months, unrelated to pregnancy, breastfeeding, or other hormonal disorders7. Studies in Iran and globally suggest that menopause age may be influenced by race, genetics, socioeconomic factors, reproductive status, physical activity, nutrition, sexual behaviors, and diseases6,8. Women now spend about one-third of their lives (20–30 years) post-menopause, during which they often face significant short- and long-term health issues. These include reduced estrogen levels, hot flashes, osteoporosis, cardiovascular diseases, urogenital atrophy, and psychosocial disorders9. The growing female population globally has led to an increase in the number of menopausal women10. A cross-sectional study of 1114 women aged 35 to 65 was conducted in Tehran from 1999 to 2009, revealing a mean menopause age of 49.6 ± 4.5 years11. In a population-based study was conducted on 894 post menopause women between 35 and 70 years old who participated in the Bandare-Kong Non-Communicable Diseases (BKNCD) Cohort Study, the mean age at natural menopause was 48.31 ± 6.34 years12. In a cross-sectional research by using the Rafsanjan Cohort Study, as a part of the prospective epidemiological research studies in Iran, the mean age at menopause among the study participants was 48.63 ± 5.37 years. 11.49% and 11.39% of the women experienced early and late menopause respectively13.

Researchers consider the age of menopause a health indicator, suggesting that understanding its influencing factors can enhance clinical and epidemiological predictions. A delayed menopause may elevate the risk of endometrial and breast cancer14. Early menopause increases the risk of cardiovascular diseases and osteoporosis. Understanding the average age of menopause and variations due to individual, social, economic, and environmental factors—such as birth rates, oral contraceptive use, obesity, and nutritional status—can help mitigate these risks. Additionally, the specific risks associated with both early and late menopause can potentially be prevented10,14.

Most existing evidence comes from Western studies, with few conducted on the Iranian population, where women’s lifestyle and reproductive characteristics differ significantly. The limited research on Iranian women primarily focuses on the average ages of menarche and menopause, along with factors influencing these ages. There is a scarcity of studies examining menstrual patterns and menopause age changes in Iran. Therefore, this cross-sectional study, based on FASA cohort data, aims to investigate the trends in menarche and menopause ages and their associated factors.

Methods

Study design

This study involved 5311 females aged 35 to 75 who participated in the first phase of FACS (Fasa Cohort Study), a population-based cohort of over 11,000 individuals aged 35–70 was enrolled from Sheshdeh, a suburb of Fasa County in Fars Province, and its 24 satellite villages15. Participants were categorized into 10-year age groups (35–44, 45–54, 55–64, and 65–75). We examined changes in age at menarche and menopause, as well as factors affecting menopause, within these age groups to identify patterns over a broad age range. In this study, menarche refers to the first menstrual cycle, and women who have not menstruated for 12 months or longer are classified as postmenopausal. Normal menarche occurs between ages 11–15, late menarche after age 15, and early menarche before age 11. Premature menopause is defined as the onset before age 40, while early menopause occurs between ages 40 and 44. Normal menopause is defined as occurring after age 4510. (Fig. 1). Menopausal age and menarche were self-reported. Predictor variables included the number of live births, education level, BMI, smoking habits, and history of infertility, tubectomy, and diabetes.

Fig. 1
figure 1

Flowchart of the sampling procedure.

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Inclusion criteria

All women in the FASA cohort study who experienced natural menopause.

Exclusion criteria

Women who experienced other forms of menopause, such as oophorectomy, or whose menopause age was indeterminate—due to factors like hysterectomy without oophorectomy or self-reported hormone therapy—were excluded from the study population.

Data analysis

Analyses were conducted using SPSS 22 software. Quantitative variables were summarized with mean and standard deviation, while qualitative variables were expressed as frequency and percentage. Independent t-tests, chi-square tests, ANOVA, and linear regression analyses were performed. The chi-square test assessed relationships between categorical variables, the t-test compared mean menopause ages between two groups, and ANOVA compared means among more than two groups. A multivariable linear regression model identified factors associated with mean menopause age, incorporating variables with P values less than 0.2 from the univariable analysis.

This article was extracted from a general medicine dissertation approved by Fasa University of Medical Sciences [code: 97143] and the University’s Ethics Committee [IR.FUMS.REC.1397.131].

Results

Participants

This study involved 5311 participants, including 1971 menopausal women, primarily married housewives with primary education. Among the diseases examined, hypertension and infertility were the most prevalent across all women and menopausal age groups. Notably, 71.3% of the women had no history of abortion, with a minimum of one and a maximum of eight abortions reported. While the mean number of abortions was similar in postmenopausal women, non-menopausal women had a significantly lower average (p < 0.001). Women who were not yet menopausal had higher mean body mass index (p < 0.001). Postmenopausal women did not exhibit a significant difference. Women who have not yet reached menopause began menstruating at a younger age than those who experienced menopause naturally. However, the average age of first birth was consistent among postmenopausal women. Furthermore, women who have not yet gone through menopause had a higher average age at first pregnancy compared to those who have (P < 0.001). Detailed findings are presented in Table 1.

Table 1 Comparison of Socio-demographic, obstetrics variables and disease in menopausal groups and non-menopausal women (n = 5311).
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Menarche and menopause

As education levels have risen, the average age at which women reach menopause has significantly decreased (p < 0.001). Factors such as being married (p = 0.005), being a housewife (p < 0.001), not smoking (p = 0.002), and having no thyroid diseases (p = 0.03) or no high blood pressure (p = 0.003) are associated with a higher mean age at menopause. Most participants experienced normal menopause at age 45 or older, followed by early menopause (ages 40–44), while few encountered premature menopause before age 40. Additionally, the majority had normal menarche (ages 11–15), followed by late menarche (after age 15), with only 5% experiencing early menarche (before age 11), primarily within the 35–45 age group. Early menarche refers to onset before age 11, while late menarche is defined as onset after age 1516. The prevalence of late menarche in this study was 10.2% (Table 2).

Table 2 Mean menopausal age based on categorical variables.
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The average age at menarche was 13.6 (1.74) years, while the average age at menopause was 49.71 (5.53) years. The largest participant group was aged 35–44, with an average menarche age of 13.4 (1.73) and a menopause age of 40.25 (4.66) years. Conversely, the smallest group was aged 65–75, with an average menarche age of 14.16 (1.99) and a menopause age of 52.27 (5.69) years. The results indicated a decrease in the mean age at menarche from 14.16 (1.99) years in the 65–75 age group to 13.40 (1.73) years in the 35–44 age group, reflecting a significant decline over time (p < 0.001). This corresponds to a reduction of 0.31 years per decade. The highest number of menopausal women was found in the 55–64 age group, while the lowest was in the 35–44 age group. Additionally, the mean age at menopause decreased from 54.49 (7.80) years in the 65–75 age group to 40.16 (3.86) years in the 35–44 age group (Table 3).

Table 3 The mean age of menopause and menarche in the 10-year age groups of the women in the study.
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Association between mean age of menopause and potential factors

The relationship between menopause age and various independent variables, including sociodemographic factors, obstetric history, and health conditions, was analyzed. Each variable was separately included in a univariate linear regression model. The results indicated that higher education, employment, and being unmarried were associated with an earlier onset of menopause. In contrast, factors such as absence of hypertension, no prior cerebrovascular accidents (CVA), older age, nonsmoking status, absence of breast cancer and thyroid disease, higher marriage age, higher age at first birth, lower number of pregnancies, lower number of living children, lower number of abortions, and higher age at menarche increased menopause age.

Subsequently, multivariable linear regression analysis assessed variables with P ≤ 0.20 using the enter method. The final model revealed significant associations with menopause age for hypertension, thyroid disease, age, and age at first birth. Findings suggested that individuals without hypertension may experience menopause approximately 0.84 years later [B = 0.84, CI = 0.34, 1.35], while those without thyroid disease may experience menopause about 0.75 years later [B = 0.75, CI = 0.07, 1.43]. Additionally, menopause age increases by 0.29 years for each additional year of a woman’s age [B = 0.29, CI = 0.24, 0.33], and by 0.11 years for every additional year at which a woman has her first child [B = 0.11, CI = 0.05, 0.17] (Table 4).

Table 4 Linear regression model to identify factors potentially associated with age at menopause.
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Discussion

In this study, the mean age at menarche was 13.6 (1.74) years, primarily observed among participants in older age groups who experienced menopause later. Notably, the mean age at menarche decreased from 14.16 (1.99) years in the 65–75 age group to 13.40 (1.73) years in the 35–44 age group.

The mean age of menarche, or a girl’s first period, in the U.S. is currently 12, as reported by the Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey. The median age at menarche decreased from 12.1 in 1995 to 11.9 between 2013 and 201717.

The average age of menarche has decreased over the past century, though the extent of this decline and its underlying factors are still debated18. In low- and middle-income countries, the age at menarche is declining rapidly, potentially faster than in high-income countries, possibly due to improved family socio-economic conditions and better nutrition19 The determinants and implications of this trend differ both between and within countries, necessitating further research to understand its causes and effects. In Europe, the median age at menarche for girls ranges from 12.6 years in Italy and Greece to 15.2 years in Russia, while in North America, it varies from 12.5 years in the United States to 12.9 years in Canada. These variations may be attributed to differences in nutritional habits, lifestyles, physical and mental stresses, and climatic conditions20. Ainy et al.‘s Tehran Lipid and Glucose Study found that daughters in Tehran reached menarche at a younger age than their mothers1. Hozoori et al. demonstrated that girls experienced menarche at a significantly younger age than their mothers21. Biro found a correlation between the ages of girls at menarche and their mothers, as well as a decline in the age at menarche over the past 20 years18. Genetic factors are key determinants of the onset of puberty; however, other elements such as nutrition, overall health, geographical location, light exposure, and mental well-being may also influence sexual development7. The observed contradictory results may stem from variations in climate and lifestyle.

This study focused solely on women over 35, so it is possible that the age of menarche has decreased further, leading to a rise in precocious puberty. Overall, the onset of puberty has shifted to earlier ages, likely due to changes in living conditions and increased resources within the region. Consequently, the health system should implement effective measures to educate adolescents on lifestyle changes to address the declining age of menarche.

In this study, the mean age at menopause was 49.71 (5.53) years. A study in Iran in 2013 reported a mean age of 50.4 years, with rural women experiencing menopause earlier than their urban counterparts, and those in industrialized areas reaching menopause later than those in non-industrialized regions22. A systematic review found that the average age of menopause among Iranian women is 48.57 years23. A systematic review and meta-analysis of 46 studies from 24 countries determined the mean age of menopause to be 48.8 years [95% CI 48.3–49.2], with earlier onset in African, Latin American, Asian, and Middle Eastern countries, and later onset in Europe, Australia, and the US24. Azizi et al. found that the mean age at natural menopause was 48.31 ± 6.34 years10. This suggests that the average age at menopause, a significant event in women’s lives, can be influenced by lifestyle and social status changes.

The current study found that participants who experienced menarche at a younger age also reached menopause earlier. Conversely, those with later menarche experienced menopause later. Farahmand et al. similarly reported that a later age at menarche correlates with a later age at menopause25. Women who begin menstruating earlier tend to experience menopause sooner, likely due to a limited pool of follicles and a fixed number of ovulation cycles. This mechanism may also clarify the association between later menopause and the use of oral contraceptives (OC)26.

Our study found that lower education (p < 0.001) and being married (p = 0.005) were associated with a higher age of menopause. Farjam et al. reported that 10.6% of women experienced late menopause (after age 55). Factors contributing to a later age at menopause included marriage, lower education, oral contraceptive use, and late menarche27. However, no significant relationship was found between the mean age at menopause and education level28. The reason for earlier menopause among single women may contributed to the fact that Married women preserve their follicles in ovaries during pregnancy and breastfeeding.

Smokers generally experienced earlier menopause. Farahmand et al. found that smoking history correlated with an earlier onset of menopause11, while Morris et al. linked increased smoking to a younger age at menopause24. Cigarette smoking lowers estrogen and raises androgen levels, leading to earlier menopause. It is considered a significant confounder related to early menopause28, with women who smoke facing a higher risk and entering menopause one to two years earlier than non-smokers29.

This study found that single women typically undergo menopause at a younger age than married women, likely due to more regular ovarian activity and sustained follicle stimulation from pituitary hormones, resulting in earlier menopause and ovarian failure30.

Our research discovered that hypertension and thyroid diseases can cause women to experience menopause at a younger age. Thyroid disorders may contribute to early menopause due to hormonal imbalances29.

The study found that the mean age at which women experience menopause has dropped significantly, from being around 65 to 75 years old to now being between 35 and 45 years old. There is no detailed information about how the average age of menopause has changed in developing countries over the last hundred years31. In contrast, in developed countries, the average age of menopause has been rising over time31. Between 1959 and 1962 and 2015–2018, the average age at natural menopause in the United States rose from 48.4 to 49.9 years, reflecting a 1.5-year increase over 60 years. Concurrently, the average reproductive lifespan grew from 35.0 to 37.1 years32.

The mean age of menopause was 0.84 years higher in women without a history of hypertension and 0.75 years higher in those without thyroid disease, compared to their diseased counterparts, according to our study. A study by Lim et al. in 2016 in Korea found that high blood pressure before age 40 is linked to earlier menopause in Korean women33. High blood pressure may accelerate menopause in women by influencing vascular health34, inflammation and hormonal changes35.

Amiri et al. (2021) found that women with generalized thyroid disorders experience natural menopause earlier, with a hazard ratio of 1.41 (95% CI 1.06–1.88)36. Lang et al. (2024) conducted a European genome-wide association study and discovered a moderate negative genetic correlation between hypothyroidism and age at menopause (rg = − 0.081; P = 0.0055), identifying the genes PPM1 F and RPL23 AP1 as potential links between thyroid function and ovarian aging37. Monterrosa-Castro et al. demonstrate that subclinical hypothyroidism significantly raises the odds of early menopause (OR 3.37; 95% CI 1.40–8.10) and premature menopause (OR 4.31; 95% CI 1.24–14.97) in Colombia38. A retrospective study by Hsieh and Ho (2021) found that autoimmune thyroid diseases, such as Hashimoto’s and Graves’, are linked to an increased risk of amenorrhea and ovarian failure39. These findings suggest that thyroid diseases, including overt and subclinical hypothyroidism and autoimmune conditions, are associated with diminished ovarian reserve and an earlier onset of menopause39. Thyroid disorders can lower the age of menopause through various mechanisms, primarily by disrupting hormonal balance, affecting ovarian health, and the impact of autoimmune diseases40.

So Chronic diseases lead to earlier menopause, and when combined with its effects on certain conditions and rising life expectancy, women experience more years with chronic illnesses. Therefore, health plans and interventions should prioritize improving women’s quality of life and reducing the burden of aging-related diseases.

Our study found that each year a woman delays having her first child corresponds to a 0.11-year increase in her age at menopause. Dratva et al. found that later births correlated with later menopause (HR, 0.934; 95% CI, 0.91–0.96)41. Delaying childbearing does not automatically result in delaying menopause; hormonal contraceptives may play a role in both.

Conclusion

Our study found that high blood pressure, thyroid disease, and older age at first delivery can lead to earlier menopause. To potentially delay this onset and improve women’s quality of life, it is essential to promptly diagnose thyroid disease and hypertension, adopt a healthy lifestyle, and ensure timely treatment.

Limitations and strange

This study analyzes data from the Persian FASA cohort, where participants self-report their medical histories, including diseases, infertility, and ages of menarche and menopause. This reliance on self-reported data may introduce recall bias, and the reported diseases are not clinically confirmed. The cohort consists primarily of postmenopausal individuals aged 35–75, which limits the investigation of menstruation-related factors. To our knowledge, this is the first large-scale epidemiological study to comprehensively examine trends in the mean age of menopause and its related factors among Iranian women.