How strong is the evidence for Zone 2?

"Zone 2 training" (low-intensity aerobic exercise performed just below the first lactate/ventilatory threshold) has become a popular longevity concept, but the best current evidence is considerably more skeptical of the specific claim than the popular narrative suggests. That evidence is currently rated emerging (38/100), built on 7 published studies, including 4 meta-analyses -- still too little to draw firm conclusions from.