(NEWS) Cardiorespiratory fitness: Meta-analysis shows 36% lower risk of depression

If your heart barely beats while climbing stairs, this may also significantly protect your brain. A new systematic review published in Nature Mental Health (March 2026) analyzed 27 cohort studies with over 4 million people from 9 countries: Individuals with high cardiorespiratory fitness showed a 36% lower risk of depression (HR = 0.64) and a 39% lower risk of dementia (HR = 0.61). Even each additional MET (Metric Energy Unit) of fitness demonstrably reduces the risk of depression further. What are the biological mechanisms behind this, and how much exercise is needed to achieve this protection?

What the meta-analysis shows

For the first time, researchers have investigated on this scale how closely cardiorespiratory fitness is related to the risk of mental and neurocognitive disorders – across all age groups.

• Study type: Systematic review study with meta-analysis – imagine it like a giant puzzle: The researchers combined 27 individual studies from 9 countries to create a complete picture.

• Number of studies / participants: 27 cohort studies, n = 4,007,638 persons; follow-up period: 4 to 29 years

• Main result 1 – Depression: High vs. low fitness level → HR = 0.64 (95% CI: 0.56–0.74). This means: Fit people have a 36% lower risk of depression. (HR = "Hazard Ratio"; an HR of 0.64 means: the risk is only 64% as high as in those who are less fit.)

• Main result 2 – Dementia: HR = 0.61 (95% CI: 0.55–0.68) → 39% lower risk for all forms of dementia; heterogeneity I² = 0% – extremely consistent result across all studies.

• Main result 3 – Psychotic disorders: HR = 0.71 (95% CI: 0.65–0.77) → 29% lower risk; data from cohort studies of male adolescents (conscripts).

• Main result 4 – Anxiety disorders: HR = 0.90 (95% CI: 0.75–1.09) – no significant effect, the confidence interval (CI) includes the value 1, i.e. no confirmed difference.

• Dose-response effect: For every +1 MET (= 3.5 ml O₂/kg/min; roughly equivalent to the difference between "walking" and "brisk walking"), the risk of depression decreases by 5% (HR = 0.95) and the risk of dementia by 19% (HR = 0.81).

• Age groups: The protective effect was similarly strong in both under 50 years of age (depression: HR 0.64; dementia: HR 0.62) and over 50 years of age (depression: HR 0.65; dementia: HR 0.60).

Mechanism: How does physical fitness protect the brain?

Imagine your brain as a high-performance factory that constantly needs energy, fresh blood and maintenance – fitness ensures that all of this runs smoothly.

• Neuroplasticity – the “construction site” in the brain: Endurance training increases the level of BDNF (Brain-Derived Neurotrophic Factor), a protein that acts like a “fertilizer for nerve cells.” New neuronal connections form more easily.

• Increased cerebral blood flow: With increasing fitness, the ability of the cardiovascular system to supply the brain with oxygen and nutrients improves – like an efficient pump that does not slow down even under load.

• Reduced systemic inflammation: Chronic inflammation in the body is considered a contributing factor to depression and dementia. Fit people have demonstrably lower levels of pro-inflammatory cytokines (e.g., IL-6, CRP).

• Improved stress regulation: Training trains the stress axis (HPA axis = hypothalamus-pituitary-adrenal axis). The result: A trained body returns to a resting state more quickly after exertion.

• Oxidative stress ↓: Regular aerobic activity strengthens the antioxidant protection system of cells and reduces harmful free radicals that can attack nerve cells.

• Improved sleep quality: Fit people sleep more deeply and restfully. Good sleep, in turn, is crucial for memory consolidation and the clearance of waste products from the brain (glymphatic system).

• Synaptic plasticity: At the cellular level, fitness improves synaptic signal transmission – nerve cells “talk” to each other more efficiently.

How much fitness is optimal? – Dosage & Application

The good news: You don't have to become a competitive athlete to protect your brain.

• Fitness measurement – VO2max & MET: Cardiorespiratory fitness is measured via maximum oxygen consumption (VO2max). One MET (Metabolic Equivalent) = 3.5 ml O₂/kg/min. Walking corresponds to approximately 3 METs, brisk walking to approximately 4–5 METs, and jogging to approximately 7–10 METs.

• Threshold: Even the jump from "low" to "moderately fit" shows the greatest risk reductions. Perfection is not necessary – regular moderate activity is sufficient.

• Recommended training methods for building CRF: endurance sports (running, cycling, swimming, Nordic walking), interval training (HIIT), brisk walks (at least 5,000–7,500 steps/day as a starting point).

• Minimum weekly dose: According to WHO guidelines: at least 150–300 minutes of moderate or 75–150 minutes of vigorous aerobic activity per week for measurable fitness gains.

• Onset of effect on CRF: Measurable improvements in VO2max are already evident after 4–8 weeks of regular training; after 12 weeks the effects are clinically relevant.

• For beginners: Even short sessions add up. 10-minute blocks spread throughout the day are just as effective as one 30-minute session.

• Continuity > Intensity: The study shows a long-term correlation. It is more important to remain moderately active for years than to train intensively in the short term.

For whom is fitness training particularly relevant?

The study results apply to everyone – but some groups benefit particularly strongly.

• People with a family history of dementia or depression: If genetic risk factors are present, fitness can play a particularly important role as a modifiable protective factor – the effect is evident across all age groups.

• People over 50: The protective effect against dementia is even slightly stronger in the 50+ age group (HR 0.60 vs. 0.62). The brain remains trainable well into old age.

• Children and adolescents: One of the included studies (Taiwan, JAMA Pediatrics) shows that fit children also have a lower risk of mental illness later in life.

• People with metabolic syndrome or type 2 diabetes: Since inflammation and insulin resistance affect brain health, the fitness effect is particularly relevant in this group.

• Women and men equally: Significant associations for depression were found in both women (HR = 0.51) and men (HR = 0.55).

• Clinical responder rate: The studies show consistent effects in all populations studied (9 countries, age groups 10–72.5 years); individual differences are to be expected.

Side effects & contraindications

Endurance training is safe for most people – however, there are some important points to consider if you have existing medical conditions.

• Frequency of side effects (at adjusted intensity): < 5% during moderate endurance training. Overtraining or abrupt increases in intensity increase the risk of injury.

• Common side effects for beginners: muscle soreness (DOMS), mild fatigue in the first 2-3 weeks, rarely temporary sleep disturbances.

• Contraindications (medical evaluation recommended): Uncontrolled cardiovascular diseases, severe heart failure (NYHA III–IV), acute inflammatory diseases, severe orthostatic hypotension.

• Drug interactions: Beta-blockers can affect maximum heart rate and therefore also CRF (VO2max) measurement. People taking medication should coordinate their training plans with their doctor.

• Pre-existing mental health conditions: In cases of acute depression or psychotic episodes, medical supervision is advisable when starting training – the study shows an association, not a replacement for therapy.

• Overtraining: Excessive training without sufficient recovery can weaken the immune system and increase cortisol – counterproductive for mental health.

• If unsure, consult your doctor: People over 65 without previous activity experience should undergo a health check before intensive endurance training.

Limitations of the overview study

1. Possible reverse causation: It is possible that people who already have early symptoms of depression or dementia reduce their physical activity – and therefore have lower fitness levels. The study shows an association, but cannot prove causation.

2. Very low quality of evidence for most outcomes: With the exception of dementia (moderate evidence), the study rates the quality of the evidence as "very low" – partly due to methodological differences between the individual studies (high heterogeneity for depression: I² = 67.9%).

3. Limited age groups: Data for children under 12 years of age and older adults over 65 years of age were very limited; generalizability to these groups is uncertain.

4. Ethnic and geographic bias: The vast majority of participants were white (of European descent or non-Hispanic US cohorts). Results may not be generalizable to other ethnicities and world regions.

5. Psychotic disorders only in men: The only data on psychotic disorders comes from cohort studies of male conscripts. Their applicability to women or other demographic groups is not certain.

⚠ Important note:

This information is for general informational purposes only and does not constitute medical advice. The study results presented show correlations, not cause-and-effect relationships. Physical training is not a substitute for medical or psychotherapeutic treatment. In the case of mental health conditions or before starting an intensive training program, always consult a qualified professional (doctor, psychotherapist).

Sources

1. Díaz-Goñi V, López-Gil JF & Bizzozero-Peroni B et al. (2026). Cardiorespiratory fitness and risk of mental disorders and dementia: a systematic review and meta-analysis. Nature Mental Health . DOI: 10.1038/s44220-026-00599-4

2. Tari AR, Walker TL, Huuha AM, Sando SB & Wisloff U (2025). Neuroprotective mechanisms of exercise and the importance of fitness for healthy brain aging. The Lancet ; 405(10484):1093–1118. DOI: 10.1016/S0140-6736(25)00184-9

3. Ross R et al. (2016). Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign. Circulation ; 134:e653–e699. DOI: 10.1161/CIR.0000000000000461