Menarche is the first occurrence of a woman’s menstruation, an event that symbolizes reproductive capacity, and which in many cultures represents a woman’s transition from childhood into womanhood [1
]. During this transition, a woman undergoes many cultural, sociological, psychological, and physical changes [1
]. The “timing of menarche” is the age when a young woman first begins menses, and is often studied in terms of describing those with early or late menarche relative to a certain population. Timing of menarche is important to women’s health in general as it has been associated with a country’s fertility and female mortality rate; specifically, menarche occurs later in countries with high mortality and fertility rates [3
]. Studies have shown that the average age of menarche has declined in industrialized countries [4
] in recent history. Some of these studies have been anecdotal in nature [5
], while others have been more systematic [4
Decreases in mean age of menarche among industrialized nations appear to be somewhat related to similarly observed increases in height (with the hypothesis being that adequate nutrition increases height and decreases age of menarche); however, this does not fully explain the relationship [6
]. Significant variance in mean age of menarche also exists based on country, suggesting the potential for genetic and/or environmental causes [14
]. Decreases in average age of menarche have been observed in developing countries as well, where the causes are often difficult to ascertain [14
]. Regarding resource-rich countries, researchers have proposed the theory that the rising obesity epidemic may be the reason for the decline in age of menarche observed in industrialized nations such as the United States of America (US) [15
]. However, one study appeared to refute this theory and found that population-level shifts in body mass index (BMI) and age of menarche were independent, but sometimes coincident processes [15
]. Studies in other industrialized nations such as South Korea, where obesity rates are relatively low, also report strong negative correlations between BMI and age of menarche [7
]. Another study found that the reduction in average age of menarche in Germany from 18 to 12–13 years, which has been occurring since the 1800s, was not driven solely by the nutritional, health, and economic changes that occurred [16
]. Therefore, the cause of the population-level reduction in age of menarche that has been observed in industrialized countries remains unknown.
When considering socioeconomic status as a factor, a recent US study found income status to be related to timing of menarche over time when the proportion of girls experiencing early menarche (<11 years old) increased over a 50 year time period only for those girls of a low socioeconomic position [10
]. In contrast, another recent study conducted in the United Kingdom (UK) spanning an 85 year time period found a decline in the timing of menarche across all socioeconomic groups [12
]. Therefore, socioeconomic status alone is unlikely to explain the changes in timing of menarche over time.
Studies of menarcheal trends have focused mainly on single factors. Some are present at the individual level, such as physical variables like BMI and height [17
], and environmental variables like socioeconomic status. Other single-factor studies have evaluated factors present at a broader scale, using climate variables like regional temperature [18
] and altitude [20
]. One recent study demonstrated the potential for interdependence between these types of factors when assessing female fecundity [21
], opening the possibility for a similar dynamic to exist in other outcomes related to reproduction, such as menarche. There is limited literature to suggest an underlying mechanism for the changes seen in timing of menarche over time. This emphasizes a need for a comprehensive summary of individual- and broad-scale effects on women’s health. Furthermore, climate change over time could be reasonably projected to influence timing of menarche, adding another layer of complexity and opportunity for study. For the purposes of this review, “climate change” is defined as any changes in the climate that have occurred, focusing specifically on changes occurring within the past hundred years. Our definition is agnostic to the causes of climate change and whether or not climate change events are man-made (i.e., anthropogenic) [22
] or purely the evolution of geologic age [23
Our systematic literature review focused on both causes and consequences of abnormal variation in the timing of menarche (either early or late). This included environmental, physiological, sociological, disease-related, and genetic contributions to menarche changes. Psychological changes were also included as either diseases or social factors, depending on the specific study. This review detailed all of the interwoven etiologies and then focused on ways that climate change could alter the timing of menarche. Our goal was to provide a comprehensive assessment of the ways that climate, and also climate change, can affect the timing of menarche, and potential consequences that this could have on women’s health.
Collectively, the studies and analysis presented in this review shed light on the multifaceted impact that climate change could have on timing of menarche as an important marker of pubertal maturity in a woman’s reproductive lifespan. This literature review focused on 112 relevant studies on timing of menarche. The review found that climate change events, including increases in hurricanes, mud/landslides, and avalanches, and increases in extreme weather events could perturb the natural timing of menarche either through increased release of toxins and pollutants buried in soil and water or by impacting food availability via crop failure. Overall, these perturbations in timing of menarche are likely to increase the disease burden for women in four key areas: mental health, fertility-related conditions, cardiovascular disease, and bone health, as revealed in our review. In summary, the climate does have the potential to impact women’s health through perturbation in timing of menarche and this, in turn, will affect women’s future risk of disease.