Longevity is the length of time a person lives, but the modern understanding goes well beyond just counting years. Scientists and public health experts now distinguish between lifespan (total years alive) and healthspan (years lived free from chronic disease or disability). Global life expectancy reached 73.1 years in 2019, though it dropped back to 71.4 years by 2021 due to the pandemic. The more interesting question, and the one driving most longevity research today, is not how to add more years but how to keep those years healthy.
Lifespan vs. Healthspan
Lifespan is straightforward: the total number of years from birth to death. Healthspan is the portion of those years spent without chronic disease or significant disability. You could live to 90 but spend the last 15 years managing heart disease, diabetes, or dementia. In that scenario, your lifespan is 90 but your healthspan is closer to 75.
The World Health Organization tracks this distinction using a metric called Healthy Life Expectancy (HALE), which estimates the average age at which chronic diseases typically begin. In 2021, global HALE was 61.9 years, nearly a full decade shorter than overall life expectancy. That gap represents years lived with illness or reduced function, and closing it is the central goal of longevity science.
What Makes Your Body Age
A landmark paper in the journal Cell identified nine biological processes that drive aging in mammals. These aren’t diseases themselves but underlying shifts that accumulate over time and eventually cause the conditions we associate with getting old. They fall into three categories.
The first category covers primary damage: your DNA accumulates errors, the protective caps on your chromosomes (telomeres) shorten with each cell division, chemical tags that control gene activity drift out of place, and your cells lose the ability to properly recycle damaged proteins. These changes are unequivocally harmful and build up steadily throughout life.
The second category is more nuanced. Cellular senescence, for example, is the process where damaged cells stop dividing and instead release inflammatory signals. In small amounts, this actually protects you from cancer by preventing damaged cells from multiplying. But as senescent cells pile up with age, the chronic inflammation they produce contributes to nearly every age-related disease. Nutrient-sensing pathways follow a similar pattern: they’re essential for growth and survival early in life but become harmful when they stay active at high levels for decades.
The third category involves system-wide breakdowns. Stem cells, which replenish your tissues, become exhausted. Communication between cells deteriorates. These integrative failures are what you experience as the visible signs of aging: slower healing, weaker muscles, declining organ function.
How Much Is Genetic
Older estimates suggested genetics accounted for only 20 to 25% of lifespan variation, with some large family-tree studies putting it as low as 6%. But a 2024 analysis published in Science reexamined over a century of Scandinavian twin data and reached a very different conclusion. The earlier estimates were skewed by extrinsic causes of death like accidents, infections, and violence, factors that have nothing to do with your biology. Once those are excluded, the heritability of lifespan jumps to about 50%.
That still leaves roughly half of the equation under your influence. And importantly, genetics determines your predispositions, not your fate. Someone with a genetic tendency toward heart disease who exercises regularly and eats well can outlive someone with “better” genes who doesn’t.
Lessons From the World’s Longest-Lived People
Five regions around the world, known as Blue Zones, produce an unusually high concentration of people who live past 100. Researchers studying these communities in Sardinia (Italy), Okinawa (Japan), Nicoya (Costa Rica), Ikaria (Greece), and Loma Linda (California) identified shared lifestyle patterns that cut across cultures and geography.
None of these centenarians follow structured exercise programs. Instead, they live in environments that require constant low-level physical activity: gardening, walking, doing housework by hand. Their diets are plant-heavy, with beans as a cornerstone and meat eaten roughly five times per month in small portions (about the size of a deck of cards). Okinawans follow a principle called “hara hachi bu,” stopping eating when they feel 80% full.
The non-dietary patterns are just as consistent. All of these communities have built-in routines for managing stress, whether that’s prayer, napping, or socializing over a glass of wine. Having a sense of purpose, what Okinawans call “ikigai,” is associated with up to seven additional years of life expectancy. Nearly all of the 263 centenarians interviewed belonged to a faith-based community, and attending services four times per month correlated with 4 to 14 extra years. Strong family bonds are universal: centenarians keep aging parents nearby, commit to life partners (associated with about three additional years), and invest heavily in their children.
Cardiorespiratory Fitness and Mortality
If there’s one measurable physical trait most strongly linked to longevity, it’s cardiorespiratory fitness, often measured as VO2 max (the maximum amount of oxygen your body can use during exercise). A large study published in JAMA Network Open analyzed over 120,000 people who underwent treadmill testing and found that elite fitness was associated with an 80% reduction in mortality risk compared to the lowest performers. Low fitness carried a mortality risk comparable to or greater than coronary artery disease, diabetes, or smoking.
This doesn’t mean you need to train like an athlete. The biggest gains come from moving out of the lowest fitness category. Walking briskly, cycling, swimming, or any activity that gets your heart rate up consistently can shift your position on that risk curve significantly.
Measuring Biological Age
Your chronological age is the number of candles on your cake. Your biological age reflects how old your body actually is at a cellular level, and the two don’t always match. Epigenetic clocks are the leading tool for measuring this gap. They work by analyzing chemical modifications on your DNA (specifically, patterns of methylation) that change predictably over time. A machine learning model trained on thousands of samples can read these patterns and estimate your biological age.
The most widely used clock, developed by Steve Horvath in 2013, examines 353 specific sites on the genome and is highly accurate in blood samples. However, these tools have real limitations. They become less precise in people over 60 and in tissues they weren’t originally trained on, particularly brain tissue. One study found that existing clocks systematically underestimate age in older individuals, which means some reported links between biological age and conditions like dementia may be unreliable. The technology is improving, but consumer-facing biological age tests should be interpreted cautiously.
The State of Longevity Drugs and Supplements
Two areas dominate longevity pharmacology right now: senolytics (drugs that clear out senescent cells) and NAD+ precursors (supplements that boost a molecule your cells need for energy and repair).
Senolytic drugs are still early in human testing. A Phase 2 trial at the Mayo Clinic gave 30 postmenopausal women a senolytic drug combination over 20 weeks and found no improvement in bone degradation markers compared to a control group. There was a brief bump in bone formation markers at two and four weeks, but it disappeared by the 20-week mark. The concept is promising based on animal studies, but human results have been underwhelming so far.
NAD+ precursors, particularly nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), have more human trial data, though the results are modest and varied. In older adults, NR at 500 mg twice daily for six weeks increased blood NAD+ levels and decreased markers associated with neurodegeneration. NMN at 250 mg daily for 10 weeks improved insulin sensitivity in postmenopausal women with prediabetes. In patients with heart failure, NR at 1 gram daily for 12 weeks raised NAD+ levels and reduced inflammatory markers in immune cells. A 28-day trial of NMN in overweight older adults showed decreases in body weight, blood pressure, and cholesterol.
These are real, measurable effects, but none of them yet demonstrate that NAD+ precursors extend human lifespan. The trials are small, short, and focused on biomarkers rather than long-term outcomes. They suggest these supplements can nudge cellular metabolism in favorable directions, but calling them “anti-aging” drugs would be getting ahead of the evidence.
What Actually Moves the Needle
The research on longevity consistently points toward the same core habits: regular physical activity (especially the kind that challenges your cardiovascular system), a plant-forward diet with moderate calorie intake, strong social connections, stress management, and a sense of purpose. These aren’t glamorous interventions, but they’re the ones with the deepest evidence base across the largest populations over the longest time periods.
Caloric restriction, specifically eating less without malnutrition, has been shown in human trials to reduce biomarkers of cellular senescence and improve insulin sensitivity. You don’t need to count every calorie. The Okinawan approach of stopping at 80% full and eating your lightest meal in the evening captures much of the same principle. The Blue Zones data reinforces that longevity isn’t built on any single habit but on an interlocking set of behaviors sustained over a lifetime.