How Yoga May Work: Proposed Mechanisms and Their Evidence

Four levels that are easy to mix up

Proposal 2: calming the stress systems

A 2017 meta-analysis pooled 42 randomized trials of practices that included yoga postures, compared with active control groups. [3] It found lower evening and waking cortisol, lower ambulatory systolic blood pressure, lower resting heart rate and higher high-frequency heart rate variability, but the interventions were heterogeneous. [3] The authors concluded that such practices appear associated with improved regulation of the sympathetic nervous system and the hypothalamic-pituitary-adrenal system. [3]

The picture is mixed. A separate review of 14 trials of heart rate variability found only two of acceptable methodological quality, and concluded there was no convincing evidence that yoga changes it. [4] Our page on cortisol and heart-rate variability covers these measures in more detail. Evidence label: mixed, and a change in a lab marker is not the same as a health outcome.

Proposal 3: brain chemistry

In one trial, healthy adults were randomized to 12 weeks of yoga or a metabolically matched walking program; the yoga group (19 people) reported greater improvement in mood and decreases in anxiety than the walking group (15 people). [5] Changes in a brain chemical called GABA, measured by scan, were correlated with the mood changes. [5] A correlation in 34 people does not show that GABA caused the improvement. Evidence label: promising but limited.

Proposal 4: lower inflammation

A systematic review of 15 randomized trials found a general pattern suggesting yoga can lower pro-inflammatory markers, though the evidence was not entirely consistent and the field was described as young. [6] A review of rodent studies on stretching found that stretching could have either therapeutic or injurious inflammatory effects depending on duration, frequency and intensity. [7] Its authors said studies paralleling yogic stretching were limited. [7] Evidence label: mixed in people, and preclinical for stretching.

Proposal 5: changes in the brain

Imaging studies have reported differences in some brain regions in people who do yoga. These are covered, with their limits, in yoga and the brain.

Proposal 6: it is exercise, plus something

Yoga postures can be a form of physical activity; see yoga and fitness. A narrative review of yoga and exercise named breath regulation, mindfulness during practice and the emphasis on holding postures as elements that distinguish yoga from other exercise. [8] Whether those elements add benefit beyond exercise has not been settled; see yoga compared with exercise in trials.

Proposal 7: expectation and context

Nobody can be blinded to whether they are doing yoga. The Cochrane review of yoga for low back pain found no trials comparing yoga with sham yoga, and all trials were at high risk of performance and detection bias because participants and providers were not blinded and outcomes were self-assessed. [9] A network meta-analysis on exercise for depression likewise suggested future studies try to blind participants and staff to reduce expectancy effects. [10] Group classes, teacher attention and expectation may all contribute; the sources we read do not separate these from other mechanisms.

What this means for you

Mechanism ideas help researchers decide what to test, but they are not reasons to expect a particular result. If you are considering yoga for a health problem, look at the trial evidence for that problem in yoga evidence by outcome. The National Center for Complementary and Integrative Health advises not using yoga to postpone seeing a health care provider about a medical problem. [1] Do not stop or change a medicine because of yoga.