insights

                                                                                                                                                                                                                   Read Time: 6 Minutes

A certain level of stress is inevitable in today’s society, and the experiences that shape the stress response may also influence sleep patterns, food intake, blood sugar imbalances, and cardiovascular disease—and vice versa—leading to chronic ill health.¹ At times of high anxiety, this bidirectional relationship can feel like an endless loop, as stress can both predispose patients to and precipitate hormonal imbalances.²

During this whole-body process, mediated by hormones and the immune system, cortisol can act as a biomarker.¹ Cortisol has a normal diurnal pattern throughout the day, normally peaking in the morning hours and bottoming out at night. In studies, deviations from this pattern are associated with signs and symptoms of adrenal dysfunction.¹

When treating hormone imbalances, a functional medicine tenet says to “start with the adrenals.” In functional medicine, evaluation of stress and application of stress management strategies can assist with downstream hormone production, transport, and processing, as well as offer low-risk, low cost, high-benefit interventions that may counter the stress response—like shinrin-yoku (forest bathing), enhanced nutrition, and physical activity.

Shinrin-Yoku (Forest Bathing)

The biophilia hypothesis, the idea that humans possess an innate tendency to seek connections with the natural environment, was introduced and popularized in 1984 by biologist Edward O. Wilson. He defined biophilia as a consequence of evolution, whereby human beings subconsciously seek connection with other forms of life.^3,4 Support for this theory comes, in part, from research demonstrating increased psychological well-being upon exposure to natural features and environments.^5-8

Research from Japan and China points to a number of positive health benefits for both psychological and physiological health associated with the practice of shinrin-yoku, also known as forest bathing.^3,9-10 Shinrin-yoku is a traditional Japanese practice of immersing oneself in nature by mindfully using all five senses, and during the 1980s, it surfaced in Japan as a pivotal part of preventive health care and healing.³ Forest environments may reduce blood pressure and heart rate,^11,12 reduce stress hormones like urinary adrenaline and salivary cortisol, increase activity of the parasympathetic nervous system, and reduce sympathetic activity.^11,13

Over the last 20 years, there has been a growing interest in greenspace and its ability to mediate the deleterious impacts of acute and chronic stress, particularly the physiologic biomarkers of stress such as cortisol.¹⁴ A 2021 review published in the International Journal of Environmental Research and Public Health suggests that greenspace interventions may have the potential for a profound impact on reducing stress as measured by cortisol and thereby reduce the physiologic stress burden across the lifespan. All four field studies on forest bathing, specifically, measured cortisol level change in two main participant conditions—a forest group where forest bathing took place in a designated forested area and an urban group (functioning as the control) where participants were in a city center.¹⁴

Studying the impact of walking on salivary cortisol levels in urban and rural settings, Kobayashi et al found a significant interaction effect between environmental setting and walking; walking in a forest environment decreased mean cortisol concentration from 9.70 to 8.37 nmol/L whereas walking in an urban environment barely changed mean cortisol concentration, from 10.28 to 10.01 nmol/L.^14,15 By contrast, participants in the study by Lee et al were passively seated in the exposure conditions, which resulted in a positive effect of forest viewing stimuli. Salivary cortisol levels were significantly lower in the forest bathing group compared to the urban viewing group (p < 0.05) at baseline and just before the stimuli (p < 0.01).^14,16 It’s important to note that studies included in this review had limitations, including small sample sizes, unmeasured variation in lifestyle factors, preexisting preference for natural settings among participants, and lack of true controls.¹⁴

An interesting 2020 prospective clinical trial on insomnia due to female hormone changes during menopause suggests that forest therapy may be an effective nonpharmacological treatment option.¹⁷ After forest bathing, which included twice-daily 30-minute forest walks and free time spent immersed in a forest education and healing center, participants experienced a 13% increase in sleep efficiency, a reduction of waking after sleep onset of approximately 48%, and an increase in total sleep time of 20 minutes.¹⁷ A 2021 forest therapy program for middle-aged women also reported an increase in positive emotions and a reduction in cortisol concentrations.^17,18 Citing the impact of chronic stress on growing populations with insomnia and poor sleep patterns in Japan, Morita et al studied forest walking to induce relaxation and improve general sleep-wake cycles in a population of 71 men and women over the course of three months. Participants reported a statistically significant correlation between increased sleep time of an average of about 54 minutes following two-hour afternoon forest walks, along with decreased anxiety.³ 

However, it is important to note that some heterogeneity in research design, aims, interventional strategy, and metrics have been identified in studies on forest bathing, with inconsistency in observed health outcomes.²⁰ More rigorous research is needed on the subject of greenspace as a mediator of the deleterious impact of stress, particularly as it relates to cortisol outcomes, and more broadly, the stress-recovery process via a variety of psychologic and physiologic pathways.²⁰

Enhanced Nutrition & Physical Activity

Cortisol also plays an important role in human nutrition, and vice versa. While cortisol itself has an appetite-stimulating effect,^21,22 extremes in nutrition intake (such as overeating or not eating enough) may impact cortisol production and secretion.^23-25

Studies suggest an upregulation of cortisol with a Western-pattern diet that includes increased amounts of refined carbohydrates and saturated fats and decreased amounts of fiber.^23,26 A 2021 cross-sectional study examining the association between hair cortisol concentration (HCC, an indicator of long-term stress) and diet among 597 preschoolers found that higher HCCs were associated with less frequent consumption of fruits and berries and more frequent consumption of sugary beverages.²⁷

In addition to nutrition, physical activity and exercise have long been shown to have beneficial effects on stress reactivity;^28,29 it may also boost levels of muscle-maintaining hormones that decline with age.^30,31 In a 2021 study of acute and delayed hormonal and blood cell responses to a high-intensity interval training (HIIT) session, after three weeks, cortisol, white blood cell count, and lymphocyte responses were decreased by an average of 42%, respectively.³² The findings indicate that short-term HIIT may blunt exercise-induced immune responses and induce rapid adaptations of the hypothalamic-pituitary-adrenal axis.³² For patients who are unable to perform vigorous exercise, regular walking may improve hormone levels and potentially improve strength and quality of life.³³

Clinical Applications

Individualized interventions like forest bathing, enhanced nutrition that highlights the anti-inflammatory aspect of a diet, and increased physical activity may help restore hormonal balance. Stress is a key mediator of a variety of poor health outcomes. Functional medicine teaches that determining the underlying cause of that stress is the most important consideration for determining subsequent interventions.

The functional medicine model shows clinicians how to identify the sources of stress in each unique individual, as well as the best way to measure cortisol levels and how to identify the different types of dysfunction that can be associated with the results. IFM has created a patient handout called “Effects of Chronic Stress” for clinician and patient use in the member toolkit, including tips for reducing stress like “spending time in nature, taking a mindfulness-based stress reduction course,” and more. To access this educational resource, log in to the IFM website and select “My Toolkit,” then search for “Effects of Chronic Stress.”

Functional medicine clinicians are also trained on the application of the “PTSD” mnemonic, which is used in the general assessment of hormone dysfunction. It helps determine if the dysfunction is related to hormone production, hormone transport, signaling sensitivity, or to an issue with detoxification. This functional medicine approach also helps identify points of leverage where physicians can apply individualized interventions to help restore hormonal balance. Learn more about tools and strategies to help patients achieve sustainable lifestyle change and improve their well-being through IFM’s new course Lifestyle: The Foundations of Functional Medicine.

For further reading on re-establishing hormonal balance, please read the following IFM-authored articles:

Balancing Thyroid Hormones Naturally 

A Functional Medicine Approach to PMS 

Why Stress Matters for Hormone Concerns 

References

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