25/08/2026
A 2026 systematic review of systematic reviews (30 reviews covering 83 unique studies and ~2.78 million participants) found:
1. Main finding: Higher sedentary time and television viewing time were consistently associated with increased all-cause mortality. Nearly all included reviews (29 of 30) reported a positive relationship between more sitting/TV time and higher death risk.
2. Why the Risk is High: Prolonged sitting reduces muscle activity, impairs glucose and fat metabolism, promotes low-grade inflammation, and is often paired with other unhealthy behaviours (snacking, lower overall movement). These effects accumulate over years and raise long-term mortality risk independently of exercise levels.
3. What else stood out: Physical activity attenuates but does not fully eliminate the risk from high sedentary time. Results held for both self-reported and device-measured sitting. The practical message is that adults benefit from both regular activity and deliberately reducing long periods of sitting or TV time.