Role of Yoga Across the Cancer Care Continuum: From Diagnosis Through Survivorship

HPA Axis

Stress activates the HPA/SNS axis, which releases hormones such as cortisol and norepinephrine. These hormones may play a role in angiogenesis, inflammation, immune suppression, and other physiological functions, and may even reduce the effect of chemotherapeutic agents.^26,27 Regular yoga practice has been shown to reduce SNS and HPA axis activity, most likely by increasing parasympathetic dominance through vagal stimulation, as demonstrated through increases in heart rate variability.²⁸ One indicator of HPA axis dysregulation, diurnal salivary cortisol rhythm, was shown to predict survival in patients with advanced breast and renal cancer.^29-33 Yoga has been shown to lead to less cortisol dysregulation due to radiotherapy and to reductions in mean cortisol levels and early morning cortisol levels in breast cancer patients undergoing radiotherapy.³⁴ This lends support to the hypothesis that yoga helps restore HPA axis balance.

Proinflammatory Cytokines

Cancer patients tend to have increased levels of inflammatory markers such as interleukin (IL)-4, IL-10, tumor necrosis factor (TNF), interferon-γ, and C-reactive protein. This increase in inflammation is associated with worse outcomes in cancer.³⁵ This association becomes highly relevant because the effect of inflammation on host cells in the tumor microenvironment is connected to disease progression.²⁶ Inflammatory cytokines are also implicated in cancer-related symptoms such as fatigue, cognitive dysfunction, peripheral neuropathy, and sleep disturbances.³⁶

Yoga is known to reduce stress and may directly or indirectly decrease inflammatory cytokines. A randomized clinical trial of a 12-week hatha yoga intervention among breast cancer survivors demonstrated decreases in IL-6, IL-1β, TNF, corticotropin-releasing factor, and cognitive complaints in the yoga group compared with those in the standard care group after 3 months.^37,38 Furthermore, Carlson et al showed that, after mindfulness-based stress reduction involving a combination of gentle yoga, meditation techniques, and relaxation exercises, breast and prostate cancer patients had reduced levels of proinflammatory cytokines and cortisol.³⁹ These reductions translated into patients reporting decreased stress levels and enhanced QOL.

Immune Function

The effects of yoga practice on the immune system have been studied in both healthy individuals and individuals with cancer. The effects on T and B lymphocytes, natural killer (NK) cells, and other immune effector cells demonstrate that meditation and yoga have beneficial effects on immune activity.⁴⁰ Hormones such as catecholamines and glucocorticoids are thought to influence the availability and function of NK cells, and, as noted above, yoga has been shown to modulate stress hormones and lead to reduced immune suppression in patients with early-stage breast cancer undergoing chemotherapy.⁴¹ Additional evidence supports the ability of yoga to reduce immune suppression in the postsurgical setting, with no observed decrease in NK cell percentage after surgery for those in a yoga group compared with a control group.⁴² This finding is relevant to patients undergoing surgical management of their cancer and highlights the impact of yoga on the immune system.

DNA Damage

Radiation damages DNA in the peripheral blood lymphocytes of patients undergoing treatment.^43,44 This damage is significant in breast cancer patients undergoing radiotherapy.⁴⁵ Stress additionally causes DNA damage⁴⁶ and is correlated to impaired DNA repair capacity.^47,48 In a study conducted by Banerjee et al, breast cancer patients were randomly assigned to a yoga group or a supportive therapy group for 6 weeks during radiotherapy.⁴⁹ Prior to the intervention, patients in the study had significant genomic instability. After treatment, patients in the yoga group experienced not only a significant reduction in anxiety and depression levels, but also a reduction in DNA damage due to radiotherapy.