The Effects of Night Shift Work on Women’s Health During the Climacteric: A Narrative Review

Abstract

Night shift work (NSW), has been associated with adverse health outcomes in women, including increased risks of metabolic disorders, cardiovascular diseases, and reproductive dysfunctions. However, the specific effects of NSW during the climacteric period remain underexplored. This narrative review aimed to examine original studies evaluating the health impacts of NSW on women in their climacteric, with a focus on menopausal timing, hormonal balance, and related symptoms. Relevant studies published in PubMed, Embase, and Scopus were reviewed in January 2025. Of 664 articles screened, 15 met the inclusion criteria. Results indicate that NSW may lead to circadian rhythm disruption, which in turn affects hormonal regulation, the timing of menopause, and the intensity of climacteric symptoms. Prolonged exposure to night shift work appears to increase the risk of metabolic and cardiovascular conditions, and certain cancers. These findings underscore the need to consider NSW as a potential modifiable risk factor for adverse health outcomes during midlife in women. They also highlight the importance of developing targeted occupational health policies and workplace interventions to mitigate these risks and promote healthier aging and quality of life.

1. Introduction

The climacteric can be defined as all of the physiological and pathological events leading up to the onset of decreased ovarian follicular function, both before and after menopause (last menstrual period), with hot flashes being the most characteristic symptom [1]. According to the Stages of Reproductive Aging Workshop system (STRAW + 10), the gold standard for defining ovarian aging stages, premenopause corresponds to the reproductive phase, prior to the climacteric, during which menstrual cycles remain regular and ovarian function is still preserved. The climacteric begins with perimenopause, characterized by progressive menstrual irregularity and marked hormonal fluctuations, and extends until the end of early postmenopause, when hormone levels reach greater stability [2]. Menopause, defined retrospectively after 12 consecutive months of amenorrhea [3], occurs within this period and represents the central milestone in the transition from the reproductive to the non-reproductive state. According to the World Health Organization [3], spontaneous amenorrhea typically occurs in women aged 45–55 years. Evidence supports the clinical importance of this transition for many women, given the health changes that can impact quality of life [2]. Moreover, the age at menopause has been identified as a marker for chronic diseases and adverse health outcomes [4].

Concomitantly, an increasing number of women undergo this reproductive transition while engaged in shift work. Shift work is an organizational arrangement of working hours designed to ensure the continuous operation of services or production, typically involving employees working in staggered schedules that may include early mornings, evenings, overnights, and weekends [5,6]. This system can encompass fixed shifts or rotating patterns (clockwise or counterclockwise), often dividing the 24 h day into two or three shifts per worker across the week [7]. When shift work includes overnight hours, normally between 23:00 and 6:00–07:00, it is referred to as night shift work (NSW). NSW has been consistently linked to circadian misalignment, reduced sleep quality and duration, and increased risks for several adverse health outcomes, including cardiovascular diseases, metabolic disorders, reproductive dysfunction, and mental health disturbances [8,9].

Insufficient sleep, circadian misalignment, melatonin suppression, and prolonged mental and physical activity are often present in shift workers [10,11,12,13]. Occupational exposure to rotating or fixed night shifts increases the risk of coronary heart disease [14], affects reproductive health [15,16], contributes to metabolic disorders [17,18], and is linked to the development of tumors such as those associated with breast cancer [19,20]. The effects of NSW may be amplified during the climacteric, as hormonal fluctuations and other physiological changes can increase susceptibility to these occupational stressors. Chronic circadian misalignment has been shown to interfere with hormonal regulation and sleep architecture [21,22,23,24], factors already destabilized in this phase of life. Hence, night work may not only intensify menopausal symptoms but also influence the timing of ovarian aging [4]. In 2019, the International Agency for Research on Cancer (IARC) classified night shift work as ‘probably carcinogenic to humans (Group 2A),’ based on limited evidence from human epidemiological studies, sufficient evidence of carcinogenicity in experimental animals, and strong mechanistic evidence [6].

Despite the known effects of night shift work on health and the clinical significance of the menopausal transition, little is understood about how occupational exposures, such as night shifts, influence the timing and symptomatology of ovarian senescence. Recent studies exploring the relationship between shift work and age at menopause report inconsistent results [25,26,27], and existing reviews tend to examine either shift work or menopausal health in isolation. To our knowledge, this is the first review to comprehensively synthesize the evidence on the potential interactions between shift and night shift work and the reproductive aging process in women, including the pre-, peri-, and postmenopausal stages. This narrative review addresses an important gap in the literature and aims to advance our understanding of how occupational factors impact women during a critical phase of endocrine and physiological transition.

2. Materials and Methods

2.1. Data Sources and Search Strategy

A structured literature search was conducted in PubMed, Embase, and Scopus in January 2025. The search included studies published from the inception of each database until January 2025, with no language restrictions. The search strategy combined the terms “menopause” AND “night shift work,” “climacteric” AND “night shift work,” “menopause” AND “shift work,” and “climacteric” AND “shift work.” No specific search for grey literature was performed, which may increase the potential for publication bias.

2.2. Inclusion and Exclusion Criteria

Studies were included if they (1) presented original data (cohort, case-control, or cross-sectional design) or (2) examined the relationship between shift and/or night shift work and health outcomes in women in the climacteric. Studies were excluded if (1) the population did not consist of women in the climacteric; (2) the population was not exposed to shift or night shift work; or (3) the focus was on a specific disease not linked to both shift work and menopause. However, studies addressing a specific disease were included if they examined the combined effect of menopausal status and shift/night shift work on that disease.

2.3. Study Selection and Data Extraction

Study selection occurred in two stages. Initially, titles and abstracts were screened for relevance. Subsequently, full-text articles were read and assessed. Reference lists of the included studies were also reviewed to identify additional relevant literature.

2.4. Data Items

From each included study, the following data were extracted: author(s), year of publication, country, study design, sample size, mean age of participants, outcomes assessed, and main findings.

2.5. Assessment of Study Quality

As this is a narrative review, no formal risk of bias assessment was performed. However, attention was paid to study design and clarity of reporting when interpreting findings.

3. Results

3.1. Study Selection

The initial search identified 664 articles. After removing 227 duplicates, 437 studies were screened by title and abstract. A total of 56 full texts were assessed, of which 43 were excluded (24 for focusing on specific diseases, 19 for using non-target populations). Two additional studies were included from reference lists, resulting in 15 studies being selected for this review. Figure 1 illustrates the PRISMA flow diagram of the selection process.

3.2. Study Characteristics

The included studies comprised seven cohort [25,26,27,29,30,31,32], six cross-sectional [33,34,35,36,37,38], and two case-control [39,40] designs, with sample sizes ranging from 49 to 80,840 participants. Study populations varied by age, occupation, and menopausal status, and addressed a wide range of health outcomes associated with shift and night work in climacteric women.

Table 1. Studies included in the narrative review on the effects of shift work and night shift work on the health of women during the climacteric.

Study	Design	Study Location	Description of Participants	Outcome	Main Findings
Khan et al., 2022 [25]	Cohort	Canada	3688 premenopausal women at baseline study. 48.9 ± 0.08 years	Variations in the age at natural menopause	NSW: higher risk of earlier menopause; RSW: higher risk of later menopause
Cassou et al., 2007 [26]	Cohort	France	1.594 postmenopausal women. Median age 52 years (range 51–52)	Age at natural menopause	Among women with no history of depression, exposure to SW was associated with earlier menopause. Among those with a history of depression, menopause occurred later in those exposed to SW.
Stock et al., 2019 [27]	Cohort (22 years)	United States	80.840 pre, peri and postmenopausal women. 35.2 ± 4.7 years (range 25–42)	Age at natural menopause	Exposure NSW, whether recent (≥10 months) or prolonged (≥11 years), is associated with an increased risk of early menopause, especially in women aged ≤45 years.
Xiao et al., 2021 [34]	Cross-sectional	China	3.518 postmenopausal women, ≥60 age ± 5.05 years	Menopausal age, menstrual duration (years of menstruation)	A history of SW was negatively associated with the age of menopause and the duration of menstruation, and positively associated with smoking and alcohol consumption.
Gomez-Acebo et al., 2014 [35]	Cross-sectional	Spain	73 day-shift workers, 42.99 ± 11.15 years and 63 night-shift workers, 43.40 ± 12.15 (range 31–55 years)	Secretion patterns of aMT6s and levels of E2, progesterone, testosterone, DHEA, and DHEAS	Testosterone levels were lower in women working night shifts, especially in the postmenopausal group
Peplonska et al., 2016 [36]	Cross-sectional	Poland	345 premenopausal women, 45.9 ± 4 years. 187 postmenopausal women, 54.5 ± 2.8 years. (range 40–60)	Levels of E2, testosterone and DHEAS	The current NSW, as well as the total duration of night work exposure throughout life, were associated with elevated E2 levels in postmenopausal women with a morning chronotype
Sawamoto et al., 2024 [33]	Cross-sectional	Japan	685 women aged 35 years or older	Association between moderate to severe menopausal symptoms (Menopause Rating Scale) and occupational factors	The lack of company support and working one-to-three night shifts per week are associated with greater severity of climacteric symptoms.
Terauchi, et al., 2014 [29]	Cohort (10 years)	Japan	9728 pre and postmenopausal women, 52.2 ± 8 years	Excessive daytime sleepiness—Epworth Sleepiness Scale, Japanese version (JESS)	Women aged 60 years or older who were currently engaged in SW were at significantly higher risk of excessive daytime sleepiness
Gromadzinska et al., 2013 [37]	Cross-sectional	Poland	359 day worker nurses, 50.2 ± 5.3 years; 349 shift worker nurses, 48.3 ± 5.2 years	GSH-Px in erythrocytes and plasma; SOD; Selenium, vitamin A, and vitamin E levels; TBARS.	Premenopausal nurses working NSW had higher GSH-Px activity than those working day shifts. Significantly lower levels of vitamins A and E were found in premenopausal women working in rotating shift systems.
Świątkowska et al., 2023 [39]	Case-control	Poland	111 postmenopausal women with breast cancer. Median 66 (IQR 8.5) years. 111 postmenopausal women without breast cancer. Median 63 (IQR 10.07) years	The association between SW and the risk of breast cancer in postmenopausal women	Postmenopausal women who had previously worked in shifts exhibited a significantly higher risk of breast cancer; ≥5 years of SW was associated with an even greater increase in breast cancer risk; the number of shifts was also linked to an increased risk of breast cancer.
Xu et al., 2020 [30]	Cohort	Australia	49 pre, peri and postmenopausal women, 54 ± 4 years	Frequency and intensity of hot flushes, daily sunlight exposure, effect modification by SW and season	Among shift workers, each additional hour of sunlight exposure was associated with a 1.4-point reduction in hot flush scores
Van Duijne et al. (2024) [31]	Cohort	Netherlands	36.273 pre and postmenopausal women. Median age 49.9 (IQR 41.8–56.0) years	Associations of NSW with weight gain among female nurses	NSW is associated with an increased risk of weight gain and obesity in postmenopausal women, with effects intensified by the frequency and continuity of shifts.
Schernhammer, et al., 2001 [32]	Cohort	United States	78.562 pre and postmenopausal women (range 30–60 years)	Comparison of the relative risk of breast cancer across categories of RSW duration, stratified by menopausal status.	Prolonged exposure to NSW was associated with an increased risk of breast cancer, particularly among postmenopausal women.
Grundy et al., 2013 [40]	Case-control	Canada	1.134 cases of breast cancer, 57.3 ±10,3 years, and 1.179 controls, 56.7 ±10,0 years	Association between long-term NSW and breast cancer risk, with analysis by hormone receptor status	Association between prolonged NSW (≥30 years) and increased breast cancer risk in postmenopausal women.
Nagata et al., 2008 [38]	Cross-sectional	Japan	206 postmenopausal women, 56.9 ± 5.8 years	Association between NSW and hormone levels	Women with a history of NSW had significantly higher estrone levels and a trend toward increased estradiol levels.

NSW: night shift work; RSW: rotating shift work; SW: shift work; aMT6s: 6-sulfatoxymelatonin; E2: estradiol; DHEA: dehydroepiandrosterone; DHEAS: dehydroepiandrosterone sulfate; GSH-Px: glutathione peroxidase; SOD: superoxide dismutase; TBARS: lipid peroxidation marker.

summarizes the main characteristics and findings of the included studies.

3.3. Climacteric Symptoms

Two studies specifically investigated climacteric symptoms. Night shift work was associated with increased severity of menopausal symptoms, especially among women with lower workplace support [33]. In contrast, increased sunlight exposure among shift workers was linked to reduced hot flashes, suggesting a role of light exposure in moderating vasomotor symptoms [30].

3.4. Age at Menopause

Five studies examined the timing of menopause. Findings were mixed: some reported earlier menopause among women with long-term or recent exposure to night shifts [26,27,34], while others suggested delayed menopause in those with rotating shifts or comorbid depression [25,26]. Several studies found that the duration and recency of night shift exposure were important modifiers. Associations were often dose-dependent and remained after adjusting for lifestyle and reproductive factors.

3.5. Hormonal and Metabolic Outcomes

Four studies explored hormonal alterations. Night shift work was associated with elevated levels of estradiol, estrone, and DHEA in postmenopausal women [35,36,38], and with reduced melatonin metabolite (aMT6s) excretion, especially among morning chronotypes [35,36]. Oxidative stress markers, such as glutathione peroxidase activity and vitamin A, were altered in night shift workers, suggesting physiological adaptations to circadian disruption [37].

3.6. Cancer and Chronic Disease Risk

Three studies reported a higher risk of breast cancer in postmenopausal women exposed to prolonged night shift work (≥5 years), with some showing dose–response relationships [32,39]. One study confirmed that the association was independent of hormone receptor status [40]. Another study linked night shift work to weight gain and obesity [31], while an additional study identified a higher risk of excessive daytime sleepiness (EDS) in older night-shift nurses [29].

3.7. Interventions and Workplace Adaptations

Few studies addressed interventions. Exogenous melatonin was suggested as a potential strategy to restore circadian rhythm, although its effects during the climacteric remain understudied [35,36]. One study discussed the importance of workplace adaptations, including flexible scheduling and supervisor training, to mitigate the impact of shift work during menopause [41].

4. Discussion

The findings of this review underscore the multifaceted impact of night shift work on women’s health during the climacteric period. As the global workforce continues to include a growing number of women navigating menopause, understanding how occupational exposures, particularly those involving circadian disruption, affect physiological and psychosocial outcomes becomes increasingly relevant. The studies reviewed reveal consistent associations between night shift work and a range of health consequences, including intensified climacteric symptoms, alterations in the timing of menopause, and hormonal and metabolic changes. These effects appear to be mediated, at least in part, by disruptions to the circadian system and its downstream influence on endocrine function and overall well-being. In the sections that follow, we examine the current evidence regarding these impacts, structured around the following key themes: symptoms, age at menopause onset, hormonal and metabolic alterations, and potential interventions and workplace adaptations.

4.1. Effects on Climacteric Symptoms

The study by Sawamoto et al. (2024) investigated the relationship between menopause symptoms and occupational factors in Japanese female workers, highlighting a significant association between night shift work (1 to 3 days per week) and the worsening of menopause symptoms. Women exposed to night shifts reported a higher likelihood of moderate to severe symptoms when compared with those who did not work at night, suggesting that circadian disruption may exacerbate these symptoms [33]. Complementing these findings, Xu et al. (2020) explored the relationship between sunlight exposure and hot flashes in menopausal women, considering the influence of shift work. The study revealed that, among shift workers, an additional hour of sunlight exposure was associated with a 1.4-point reduction in hot flash scores. This effect was not observed in daytime workers, indicating that sunlight exposure may play a significant role in mitigating vasomotor symptoms in women exposed to circadian disruption caused by shift work [30]. These results suggest that circadian rhythm dysregulation may amplify the intensity and frequency of hot flashes in menopausal women.

4.2. Effects on Menopause Onset Age

The age of natural menopause is considered a marker of health and aging [27,30,33,34]. Recent studies have explored the relationship between shift work and the onset of menopause, with mixed results. One study found that women exposed to rotating shift work were more likely to experience late menopause, while those currently working night shifts had an increased risk of early menopause. Factors such as smoking, high BMI, and lower parity were associated with early menopause, whereas moderate alcohol consumption and higher parity were linked to late menopause. According to this study, circadian disruption caused by shift work may affect estrogen production, influencing the timing of menopause [25]. Among women with a history of depression, recent exposure to shift work was associated with later menopause, with a trend toward significance (p = 0.08). The authors suggest that, although shift work may affect circadian rhythms and reproductive health, the observed associations were weak or inconclusive [26].

Another study demonstrated that recent rotating night shift work was moderately associated with an increased risk of early menopause. Women who had worked night shifts for 10 months or more in the past two years had a higher risk, especially those with 10–19 months of exposure. Among women under 45 years old, working night shifts for more than 10 years increased the risk of early menopause by 22% (11–20 years of exposure) and 73% (more than 20 years of exposure). Exposure to 20 or more months of night shifts in the past two years also increased the likelihood of early menopause. The authors suggest that circadian rhythm dysregulation, possibly due to melatonin suppression, may negatively affect ovarian function [27]. Xiao et al. (2021) also investigated this relationship, finding that women with a history of shift work experienced earlier menopause and a shorter reproductive period. After adjusting for factors such as passive smoking and alcohol consumption, the analysis confirmed a negative association between shift work and menopause age, suggesting that this exposure may accelerate the decline in reproductive function [34].

4.3. Hormonal and Metabolic Effects

The study by Gómez-Acebo et al. (2014) analyzed the effects of rotating shift work, including night shifts, on the levels of 6-sulfatoxymelatonin (aMT6s), cortisol, and sex hormones in pre- and postmenopausal women. Postmenopausal women working night shifts had higher levels of estradiol and dehydroepiandrosterone (DHEA). Additionally, both pre- and postmenopausal night shift workers had lower aMT6s excretion, suggesting circadian disruption in both groups [35]. Peplonska et al. (2016) investigated chronotypes and found that prolonged night shift work (>15 years) was associated with higher estradiol (E2) levels in postmenopausal women with a morning chronotype. This finding suggests that night shift work affects morning-oriented individuals more, possibly due to circadian rhythm dysregulation and reduced melatonin synthesis. For premenopausal women, the associations were not significant, indicating a specific impact after ovarian function cessation [36].

Nagata et al. (2008) observed that postmenopausal women who stayed awake after 01:00 a.m. had higher estradiol levels, while those with a history of night shift work had higher estrone levels. There was also a trend toward reduced urinary aMT6s levels in women who stayed up late, reinforcing the effect of nighttime light exposure on melatonin suppression. However, no direct association between melatonin and estrogen was found, leaving the role of melatonin as a mediator uncertain [38]. The authors found, when investigating the oxidative–antioxidative balance in nurses, that night shift workers showed higher antioxidant enzyme glutathione peroxidase activity, proportional to the number of night shifts worked per month. Postmenopausal women working day shifts had higher lipid peroxidation (TBARS) levels, while those working night shifts showed increased vitamin A levels, suggesting metabolic adaptation to oxidative stress [37].

Świątkowska et al. (2023) highlighted that shift work increases the risk of breast cancer in postmenopausal women, especially with prolonged exposure (≥5 years). The risk was even higher among overweight women, reaching nearly 10 times [39]. Schernhammer et al. (2001) also observed that postmenopausal nurses with 30 or more years of night shift work had a significantly higher risk of breast cancer, with a clear dose–response relationship [32]. A Canadian study [40] expanded this association to various occupations, confirming that the risk is not limited to healthcare professionals and is independent of estrogen and progesterone receptor status (ER/PR).

Van Duijne et al. (2024) observed that postmenopausal women working night shifts had a higher risk of weight gain and obesity, especially with a higher number of nights worked [31]. Terauchi et al. (2024) found that NSW significantly increased the risk of excessive daytime sleepiness (EDS) in nurses aged 60 and above, which could compromise quality of life and increase medical errors [29].

4.4. Treatment

The importance of adapting work environments to better support women in menopause, especially those involved in night shifts, was discussed. Measures such as flexible hours, psychological support, and interventions to improve sleep quality can help mitigate the negative impacts of this type of work on workers’ health [29]. Additionally, the consensus recommendations from The Menopause Society suggest that companies review support policies and promote training for managers. The consensus also emphasizes that addressing menopause in the workplace can reduce absenteeism costs, improve talent retention, and create a more inclusive and productive environment for all employees [41].

Exogenous melatonin supplementation was also suggested to restore circadian rhythms and improve sleep quality in night shift workers [35,36]. However, there is insufficient information on its effects during the climacteric phase.

4.5. Strengths, Limitations, and Future Directions

A major strength of this review lies in its focused examination of the intersection between occupational exposure to night shift work and women’s health during the climacteric, a topic that remains underexplored in the literature. By synthesizing findings from recent studies across diverse populations and menopausal stages, this review provides a comprehensive overview of potential biological and psychosocial impacts.

However, some limitations must be acknowledged. First, the majority of included studies are observational and subject to residual confounding, particularly regarding lifestyle factors such as diet, physical activity, smoking, and stress. Additionally, most of the reviewed research focuses exclusively on cisgender women, limiting the generalizability of findings to all individuals undergoing menopausal transition. Although this study did not include transgender individuals, it is plausible that the climacteric period may present distinct characteristics when certain exogenous hormones are used during this phase of life.

From a policy and practice perspective, the findings highlight the urgent need for workplaces to adopt more inclusive health policies that consider the physiological changes associated with menopause. Strategies could include flexible scheduling, access to sleep and circadian hygiene resources, targeted health screenings, and training for supervisors on the needs of aging female workers.

Future research should prioritize prospective and interventional studies to more accurately establish causal relationships between shift work and climacteric outcomes, overcoming the limitations inherent in cross-sectional and retrospective designs. In particular, trials evaluating the effectiveness of interventions, such as melatonin supplementation, are essential to determine strategies that may alleviate circadian disruption and improve health outcomes during the menopausal transition. Moreover, expanding the scope of research to include gender-diverse populations would enhance the inclusivity and generalizability of findings, ensuring that future evidence better reflects the experiences of all individuals affected by reproductive aging.

5. Conclusions

These insights underscore the need for further investigation into the effects of NSW as potential modifiable risk factors for menopausal health outcomes. While emerging studies suggest that circadian misalignment caused by NSW may have significant implications for the age of menopause and other aspects of reproductive aging, there remains a notable gap in the existing literature on this topic. Given the impact of the menopausal transition on individuals who experience it, it is essential to prioritize research in this area. Understanding how work schedules influence menopausal experiences could guide the development of workplace policies that not only address circadian disruption but also promote the well-being of those experiencing this natural life transition.

The authors acknowledge that some individuals going through menopause may identify differently from the gender and pronouns used in this review, and that all studies included here focused solely on cisgender women.