What is the difference between lifespan and healthspan?
Lifespan is total years lived. Healthspan is the years lived without chronic disease or disability. Average lifespan rose in developed countries, healthspan did not keep pace — most people spend their last 8-10 years in chronic illness.
The practical aim is to compress that gap: climbing stairs, thinking clearly and staying independent at 80.
What are the four pillars of longevity?
Cardiorespiratory fitness (VO2max) is the single strongest predictor of all-cause mortality; moving from low to average fitness rivals smoking cessation in benefit.
Muscle mass and strength: grip and leg strength predict independence in later life. Two resistance sessions a week is the floor.
Metabolic health: waist circumference, fasting insulin, HbA1c and the triglyceride/HDL ratio.
Sleep and stress recovery: glymphatic clearance happens during sleep; chronic deprivation accelerates cognitive ageing.
Which popular approaches are overrated?
Supplements produce small effects in isolation and are a distraction before the four pillars are in place.
Intermittent fasting mostly works by making calorie control easier; if it cuts protein intake it risks muscle loss.
Cold and heat exposure help recovery and mood, but do not substitute for VO2max and muscle.
Where should you start?
Track resting heart rate weekly, average daily steps and sleep regularity. After three months those curves tell you more than any supplement.
fjt merges those signals into a single felt-age indicator from daily check-ins and phone step data.
