Shifting focus from the broader benefits of lactation, it is essential to highlight the underlying biological mechanisms that make these advantages possible. Human lactation is a complex process involving the mammary gland, hormonal regulation, and milk composition. This intricate system is coordinated by an interplay of hormones that ensure the successful production and ejection of milk, providing nourishment for the infant. The mammary gland, primarily influenced by estrogen, prolactin, and cortisol, undergoes significant changes to prepare for lactation ( Alex et al., 2020). During pregnancy, estrogen stimulates the proliferation of ductal structures within the mammary glands, while progesterone promotes the formation of alveolar structures necessary for milk production ( Alex et al., 2020). Cortisol also plays a role in mammary gland development by enhancing the effects of prolactin and other lactogenic hormones ( Kabotyanski et al., 2006).

Lactogenesis, the onset of milk production, is divided into two stages: Lactogenesis I occurs during pregnancy when the mammary gland develops the capacity to secrete milk but is inhibited by high levels of progesterone, and Lactogenesis II begins postpartum, around 2-3 days after childbirth, when the drop in progesterone levels triggers the onset of copious milk secretion ( Sadovnikova et al., 2020). This stage is characterized by increased blood flow, oxygen, and glucose uptake by the mammary gland, essential for milk synthesis ( Neville & Morton, 2001). The hormonal axis regulating lactation involves a finely tuned balance of various hormones, primarily prolactin and oxytocin, and their feedback mechanisms ( Trott et al., 2012). Prolactin is synthesized and released by the anterior pituitary gland in response to the stimulation of the nipples by suckling ( Trott et al., 2012). This stimulus is transmitted via neural pathways to the hypothalamus, where the inhibition of prolactin-inhibiting factor (dopamine) allows for the increased release of prolactin from the pituitary ( Grattan, 2015). Prolactin is essential for the initiation and maintenance of milk production, promoting the synthesis of milk proteins, lactose, and lipids in the mammary alveolar cells ( Grattan, 2015; Trott et al., 2012).

Oxytocin, synthesized in the hypothalamus and stored in the posterior pituitary gland, is released into the bloodstream in response to suckling ( Crowley, 2014). It facilitates the ejection of milk from the mammary glands by causing the myoepithelial cells surrounding the alveoli to contract, expelling milk through the ductal system to the nipple ( Crowley, 2014). Milk synthesis occurs through various cellular mechanisms within the mammary alveoli, involving the uptake of precursors from maternal blood and their conversion into milk components, such as lactose, casein, whey proteins, and lipids ( Neville & Morton, 2001; Sadovnikova et al., 2020). The composition of human milk is dynamic and influenced by several factors, including maternal diet, body composition, genetics, and environmental factors. Nutritional intake and body fat stores of the mother can affect the quantity and quality of milk produced, while genetic factors play a role in determining milk volume, composition, and the ability to sustain lactation ( Han et al., 2019; Wheelock et al., 2010). External factors, such as stress, exposure to pollutants, and overall health, can also impact lactation.

The onset and maintenance of lactation are tightly regulated by endocrine changes that occur during pregnancy and the postpartum period. During pregnancy, elevated levels of estrogen and progesterone prepare the mammary glands for lactation but inhibit milk secretion ( Neville & Morton, 2001; Sadovnikova et al., 2020). Postpartum, the significant drop in progesterone levels after delivery, combined with the continued high levels of prolactin and the initiation of oxytocin release through suckling, ensures the successful transition to active milk production and ejection ( Crowley, 2014). Understanding the intricate anatomy and physiology of lactation is crucial for supporting breastfeeding, helping healthcare providers offer better guidance and interventions to ensure successful breastfeeding and maximize health benefits for both mother and child.

Pathophysiology of the effects of heat on lactation

Many of the studies done to examine the effects of heat stress on lactation have been conducted in non-human mammalian animal models; however, it is possible to extrapolate the effects of heat stress on lactating humans due to the similarities between human and bovine and porcine animal models.

Heat stress can impair lactation by affecting both the endocrine system and the overall physiological state of lactating mammals ( Han et al., 2019). Elevated temperatures can lead to dehydration, which significantly impacts the body’s ability to produce and secrete milk. Dehydration reduces blood volume and flow to the mammary glands, thereby decreasing the supply of essential nutrients and precursors required for milk synthesis ( Wheelock et al., 2010). This reduction in blood volume can lead to decreased renal function and reduced clearance of metabolic waste, further complicating the physiological state of the lactating animal.

Additionally, heat stress can alter the hormonal balance necessary for lactation ( Han et al., 2019; Wheelock et al., 2010). Prolactin and oxytocin levels can be disrupted by stress hormones such as cortisol, which is elevated in response to heat stress. Cortisol can inhibit the release of prolactin from the anterior pituitary gland, which is crucial for the synthesis of milk proteins, lactose, and lipids. This inhibition can lead to a significant decrease in milk volume ( Rhoads et al., 2010; Ponchon et al., 2017; Syam et al., 2022). Moreover, cortisol can affect the release of oxytocin from the posterior pituitary gland, impairing the milk ejection reflex. Without adequate oxytocin, the myoepithelial cells surrounding the alveoli fail to contract effectively, reducing the efficiency of milk expulsion from the mammary glands ( Haaksma et al., 2011).

Heat stress can also increase the levels of catecholamines (epinephrine and norepinephrine), which are stress-related hormones that further inhibit oxytocin release and exacerbate the difficulties in milk ejection ( Haldar & Bade, 1981). The combined effect of elevated cortisol and catecholamines can lead to a cycle of stress and reduced lactation, impacting the mother’s ability to breastfeed effectively.

The physiological stress from elevated temperatures can also lead to systemic inflammation, which can affect the mammary glands. Inflammatory cytokines such as IL-6 and TNF-α may increase, potentially disrupting normal cellular functions within the mammary glands and further impairing milk production and quality ( Abdelnour et al., 2019; Chen et al., 2023). Additionally, heat stress may exacerbate underlying health conditions, such as hypertension or diabetes, which can further complicate lactation.

In summary, the impact of heat stress on lactating individuals is multifaceted, involving dehydration, hormonal imbalances, systemic inflammation, and potential exacerbation of pre-existing conditions. These factors collectively impair milk production and ejection, posing significant challenges for breastfeeding mothers in hot climates.

Excess heat’s effects on lactating infants. For infants, the impact of heat on lactation can be severe. Reduced milk production due to heat stress can lead to insufficient nutrient intake, affecting the infant’s growth and development. Breast milk provides essential hydration, particularly in hot climates, and any reduction in its availability can increase the risk of dehydration in infants ( Bernabucci et al., 2013). Furthermore, the quality of breast milk can be compromised under heat stress, with potential changes in its composition affecting the balance of nutrients, antibodies, and other bioactive components critical for the infant’s health ( Bernabucci et al., 2013).

Overall, health risks. Both lactating individuals and their infants face increased health risks during periods of high heat. Lactating individuals experiencing heat stress may suffer from symptoms such as fatigue, dizziness, and heat exhaustion, which can affect their ability to care for their infants effectively ( Lefebvre et al., 2024). For infants, the combination of reduced milk intake and increased susceptibility to heat can lead to severe dehydration, electrolyte imbalances, and heat-related illnesses, potentially requiring medical intervention ( Lefebvre et al., 2024).

In summary, understanding the pathophysiology of the effects of heat on lactation is crucial for developing strategies to mitigate these risks. Ensuring adequate hydration, maintaining a cool environment, and monitoring both lactating individuals and their infants for signs of heat stress are essential steps in safeguarding their health during periods of elevated temperatures.

Transitioning from the biological complexities of human lactation to its wider contexts, human lactation also has profound socioeconomic implications. The economic impact of lactation is substantial, as human milk production contributes significantly to national economies by reducing healthcare costs ( Alex et al., 2020). Lactation adequacy is influenced by social and health factors, underscoring the critical role of breastfeeding in developing countries ( Kabotyanski et al., 2006). The evolutionary and environmental influences on human lactation highlight its psychosocial, nutritional, and economic significance ( Neville & Morton, 2001; Sadovnikova et al., 2020). Various demographic, physical, social, and psychological variables influence breastfeeding duration ( Trott et al., 2012). Additionally, the nutritional and health aspects of human lactation underscore its importance in both developed and developing countries ( Crowley, 2014; Neville & Morton, 2001).

Climate change significantly impacts health and nutrition, particularly for vulnerable populations. One critical area of concern is the effect of temperature extremes on maternal and infant health ( Bao et al., 2020; Lefebvre et al., 2024; Han et al., 2019). Extreme temperatures can lead to increased incidences of heat stress, dehydration, and heat-related illnesses, which are particularly dangerous for pregnant women and infants ( Bao et al., 2020). Pregnant women exposed to high temperatures have a higher risk of adverse birth outcomes, such as preterm birth and low birth weight. Infants are also at risk as their thermoregulatory systems are not fully developed, making them more susceptible to heat-related illnesses ( Bao et al., 2020).

A range of studies have highlighted the significant impact of temperature extremes on maternal and infant health. Research has found that heat exposure during pregnancy can lead to adverse outcomes such as preterm birth, low birth weight, and stillbirth ( Weng et al., 2017). Further studies emphasized the increased risk of maternal hospitalization and infant mortality associated with extreme heat ( Ponchon et al., 2017; Syam et al., 2022). Expanded findings have identified a link between prenatal exposure to extreme temperatures and severe maternal morbidity. Additional research has highlighted the disproportionate impact of extreme temperatures on Black and Hispanic mothers, suggesting that these disparities may be exacerbated by future temperature increases ( Haaksma et al., 2011; Haldar & Bade, 1981).

Moreover, climate change disrupts food security and nutrition. Changes in weather patterns, such as prolonged droughts and increased frequency of extreme weather events, can negatively affect agricultural productivity, leading to food shortages and increased prices ( Abdelnour et al., 2019). This can result in malnutrition, especially in communities that rely heavily on subsistence farming ( Chen et al., 2023; Bernabucci et al., 2013). The nutritional quality of food can also be compromised due to climate-induced changes in soil health and crop nutrient content, further exacerbating the problem ( Maheshwari, 2022).

Water scarcity, another consequence of climate change, has significant implications for hydration and lactation ( Geissler et al., 1978; Kim & Yi, 2020). Adequate water intake is crucial for maintaining maternal health and ensuring sufficient milk production ( Geissler et al., 1978). In regions facing water shortages, women may struggle to stay hydrated, impacting their overall health and ability to lactate effectively. This situation is particularly dire in areas where access to clean water is already limited, and the added stress of water scarcity can severely affect both maternal and infant health ( Prentice & Prentice, 1995).

Lactating females face increased physiological demands, making them particularly vulnerable to the impacts of climate change. During lactation, women require additional calories, nutrients, and hydration to produce sufficient breast milk ( Cowie et al., 1979). Climate-related challenges, such as heat stress and water scarcity, can hinder their ability to meet these increased demands, thereby affecting milk production and quality ( Prentice & Prentice, 1995; Thulier & Mercer, 2009).

In addition to socio-economic disparities, climate-related stressors, such as natural disasters and displacement, significantly impact lactating individuals. Different populations experience varying levels of vulnerability to climate change, with low-income and rural communities often being the most affected. These populations typically have limited access to healthcare, nutritious food, and clean water, making it difficult to cope with the additional stressors brought on by climate change ( Delgado et al., 1985). Rural areas may face increased isolation during extreme weather events, further limiting their access to necessary resources and support ( Casey & Hambidge, 1983).

Moreover, the influence of heat stress on milk production and composition is a critical area of concern. Climate-related stressors, such as natural disasters and displacement, also significantly impact lactating females. Natural disasters can lead to the displacement of communities, disrupting access to food, water, and healthcare ( Kuehn & McCormick, 2017). Displacement can also result in increased exposure to unsanitary conditions and infectious diseases, which can negatively affect maternal and infant health ( Kuehn & McCormick, 2017; Kim et al., 2019). Ultimately, the stress and trauma associated with displacement can further impair lactation, leading to a decline in milk production and quality.

The influence of heat stress on milk production and composition is a critical area of concern. High temperatures can lead to dehydration, which reduces a woman’s ability to produce milk ( Kim & Yi, 2020). Heat stress can also alter the composition of breast milk, potentially reducing its nutritional value and affecting infant growth and development. Ensuring adequate hydration and managing heat exposure are essential for maintaining effective lactation under changing climatic conditions.

Socioeconomic status (SES) is a major determinant of health outcomes, including those related to lactation ( Pérez-Escamilla & Moran, 2022). Low-income families often have limited access to healthcare, nutritious food, and clean water, all of which are essential for maintaining optimal health and lactation ( Adler & Newman, 2002). Climate change exacerbates these challenges by increasing the frequency and severity of extreme weather events, such as droughts and heatwaves, which disproportionately affect low-income communities ( Gregory et al., 2023). These events can disrupt access to essential resources, further compromising the health of lactating mothers and their infants.

Geographic location also plays a crucial role in health disparities. Rural and remote areas, particularly in developing countries, often lack adequate healthcare infrastructure and resources ( Reilly, 2021). Breastfeeding support disparities are apparent, particularly in rural areas where access is limited and inequities are tied to socioeconomic status ( Grubesic & Durbin, 2017). These regions are more vulnerable to the impacts of climate change, including water scarcity and food insecurity, which directly affect lactating individuals. Urban areas, while having better access to healthcare, are not immune to disparities. Low-income urban neighborhoods may face challenges such as heat islands and poor air quality, further impacting maternal and infant health ( Howarth & Eiser, 2023).

Racial and ethnic minorities are disproportionately affected by climate change and its health impacts ( Weaver et al., 2023). In many regions, Black, Indigenous, and People of Color (BIPOC) communities face systemic barriers to healthcare and are more likely to live in areas with higher exposure to environmental hazards. These communities often experience higher rates of pre-existing conditions, which can be exacerbated by climate-induced stressors, further complicating lactation and infant health ( Burbank et al., 2023; Morello-Frosch et al., 2011). For example, Black and Hispanic mothers have been shown to have higher rates of adverse birth outcomes linked to extreme heat exposure ( Borrell et al., 2022; Dzekem et al., 2023).

The concept of intersectionality highlights how various aspects of a person’s identity, such as race, gender, socioeconomic status (SES), and geographic location, intersect to create unique experiences of disadvantage and privilege ( Williams et al., 2012). This framework is critical for understanding the compounded vulnerabilities faced by lactating individuals who belong to multiple marginalized groups. For instance, a low-income, rural, Black mother may encounter a multitude of barriers that singularly and collectively impact her health and lactation experience ( MacGregor & Hughes, 2010). Firstly, limited access to healthcare is a significant challenge for low-income, rural populations ( Asiodu et al., 2021). Healthcare facilities may be scarce and distant, leading to delays in receiving necessary prenatal and postnatal care. This can hinder the establishment and maintenance of breastfeeding. Additionally, financial constraints may limit access to resources such as lactation consultants, breast pumps, and nutritional support, all of which are vital for successful breastfeeding ( Francis et al., 2020; Gorman, 2020).

Secondly, exposure to extreme weather conditions, exacerbated by climate change, poses additional risks. In rural areas, infrastructure may be inadequate to cope with extreme heat, affecting the availability of clean water and cooling mechanisms. This can lead to dehydration and heat stress, further complicating the physiological process of lactation and the overall health of the mother and infant ( Lusambili & Nakstad, 2023; Roos et al., 2021).

Lastly, systemic racism adds another layer of complexity. Discriminatory practices within the healthcare system can result in biased treatment and a lack of culturally competent care. This may lead to mistrust in healthcare providers and reluctance to seek help, thereby affecting the quality of care received ( Witt et al., 2022). Furthermore, social determinants of health, such as housing instability, food insecurity, and limited educational opportunities, disproportionately affect Black communities, amplifying the challenges faced by low-income, Black mothers ( Brailey & Slatton, 2024; Greenberg et al., 2022).

In summary, intersectionality provides a comprehensive lens through which to view the compounded adversities faced by lactating individuals from multiple marginalized backgrounds. Addressing these layered challenges requires a multifaceted approach that considers the intricate interplay of race, gender, SES, and geographic location to improve health outcomes and support equitable lactation practices ( Carter et al., 2021).

Malnutrition in lactating women can lead to a decrease in milk production and a reduction in the quality of breast milk ( Runkle et al., 2022). Dehydration further complicates this issue, as it not only reduces milk volume but can also affect the mother’s overall health, making it more difficult for her to care for her infant ( Kim & Yi, 2020). Addressing malnutrition and ensuring access to clean water are crucial for supporting lactating women in a changing climate.

In addition to the challenges of malnutrition and dehydration, environmental toxins and pollutants, increasingly prevalent due to climate change, also affect milk quality ( Rylander et al., 2013). Pollutants such as heavy metals and chemicals can accumulate in breast milk, posing health risks to infants ( Hasan & Hussain, 2020). Climate change can exacerbate the spread of these toxins through increased flooding, which can contaminate water supplies and agricultural lands ( Kiprutto et al., 2015). Monitoring and mitigating exposure to environmental toxins are essential steps in protecting maternal and infant health.

Numerous studies document the effects of climate change on lactating females, providing valuable insights into this critical issue. For instance, research has shown that heat stress can significantly reduce milk production and alter its composition, while malnutrition and dehydration further exacerbate these effects ( Hema et al., 2023; Lake et al., 2012). These studies highlight the importance of addressing climate-related challenges to support lactating women and their infants.

Analysis of data from various geographical regions reveals the widespread impact of climate change on lactation. In regions with high temperatures and frequent droughts, such as parts of Africa, Central and South America, and South Asia, lactating women face significant challenges in maintaining adequate hydration and nutrition. These regions also often experience food insecurity, further complicating efforts to support maternal and infant health ( Sultana & Mostafa, 2023; DeNicola et al., 2015; Xie et al., 2022; Bentley, 1998; Butte et al., 2001). Understanding regional differences in vulnerability and adaptive capacity is essential for developing effective interventions.

Case studies highlight critical issues and adaptive responses to climate change impacts on lactation. For example, in some communities, local initiatives have been implemented to provide clean water and nutritional support to lactating women ( Josefson et al., 2023). These initiatives often involve community-based education programs and partnerships with local organizations to ensure sustainable access to resources ( Josefson et al., 2023; Chen et al., 2020; Winter et al., 2019). By examining these case studies, we can identify successful strategies and best practices that can be adapted and implemented in other regions facing similar challenges.

Nutritional support is crucial for lactating females, especially in regions affected by climate change. Interventions should focus on providing access to nutrient-rich foods and supplements to meet the increased caloric and nutritional demands of lactation. Governments and organizations should implement policies to secure food and water supplies in vulnerable regions. This includes investing in sustainable agriculture, improving water management systems, and providing emergency food and water supplies during climate-related disasters. Public health initiatives should aim to reduce exposure to environmental toxins that can contaminate breast milk. This includes monitoring and regulating pollutants, educating communities about safe practices, and providing resources to minimize exposure. Community-based programs can provide essential support and education to lactating mothers. These programs can offer breastfeeding education, nutritional counseling, and access to clean water and healthcare services, enhancing resilience against climate-related stressors.

Climate policies should explicitly address the needs of lactating women, ensuring they receive the necessary support and resources to maintain healthy lactation despite climate challenges. Advocates should push for the inclusion of maternal and child health considerations in climate action plans at local, national, and international levels. This ensures that the unique needs of lactating women are not overlooked in broader climate initiatives. Increased funding is needed to support research on the impacts of climate change on lactation. This includes epidemiological studies, interventions, and policy analyses to develop effective strategies for supporting lactating women in a changing climate.

The social-ecological model examines how individual, interpersonal, organizational, community, and policy factors interact to influence health outcomes ( Figure 1) ( Khajehaminian et al., 2019). Applying this model to lactation and climate change helps identify the multiple levels of influence and potential intervention points. At the individual level, educating lactating women about the impacts of climate change and strategies for maintaining health and milk production can enhance personal resilience.

Encouraging behaviors such as staying hydrated, consuming nutrient-rich foods, and managing heat exposure can help lactating women adapt to climate stressors. Strengthening social support networks can provide emotional and practical support to lactating women, helping them cope with climate-related challenges. Involving family members and partners in efforts to support lactation can enhance the effectiveness of adaptive strategies and provide additional resources and support.

At the organizational level, workplaces should adopt policies that support lactating mothers, such as providing flexible schedules, lactation rooms, and access to clean water and nutritious food. Healthcare facilities should be equipped to handle the impacts of climate change, ensuring they can provide adequate care and support to lactating women. Communities can develop interventions to ensure that resources such as clean water, food, and healthcare are available during climate-related events. Local support groups and peer counselors can offer practical advice, emotional support, and resources to lactating women, helping them navigate climate challenges.

Advocacy efforts should focus on integrating lactation considerations into climate policies at national and international levels, ensuring that the needs of lactating women are prioritized. Climate adaptation and mitigation strategies should include specific measures to protect maternal and child health, addressing the unique vulnerabilities of lactating women. Collaboration across disciplines can lead to more effective strategies for addressing the impacts of climate change on lactation. Community-driven initiatives can provide tailored solutions that align with broader policy goals, ensuring that local needs and perspectives are integrated into climate and health strategies. By addressing the issue of climate change and lactation through a social-ecological lens, we can develop comprehensive strategies that support lactating women at multiple levels of influence. This holistic approach is essential for building resilience and ensuring the health and well-being of both mothers and infants in a changing climate.

Future research should focus on identifying and addressing gaps in our understanding of how climate change affects lactation in humans. This includes studying the physiological, nutritional, and environmental factors that influence lactation under different climatic conditions. Longitudinal and cross-sectional studies are needed to examine the long-term impacts of climate change on lactation and maternal and infant health. These studies can provide valuable insights into how climate-related stressors affect lactation over time. Interdisciplinary research is essential to fully understand the complex interactions between climate change, nutrition, and public health. Collaboration between climate scientists, nutritionists, and public health experts can lead to more comprehensive and effective strategies for supporting lactating women.