No supplement was tested.
The study used one complete food at two intake levels. It does not prove that any antioxidant, omega oil, NAD+ product, proprietary blend, or senior chew extends dog lifespan.
It also does not give pet parents a do-it-yourself calorie-restriction protocol for an older dog. The dogs were monitored from puppyhood in a research setting. Weight loss in an adult or senior dog can be helpful, harmful, or urgent depending on body condition, muscle, disease status, medication, appetite, and veterinary history.
The safe translation is this: body condition is a first-order variable. Product claims that skip it are incomplete.