The desire to live eternally has been around almost as long as humans have been aware of death. Survival is human nature, but is expanding the limits of the human lifespan actually possible?
The mean life expectancy for men and women today is about 79 years.  Compared to life expectancy 50 years ago, we’re living 8 years longer on average.  That’s good news. But many scientists, including InsideTracker founder and Chief Scientific Officer, Dr. Gil Blander, believe we can extend our current lifespan and healthspan much longer.
Why do humans age?
Aging is a universal experience for all life in the universe. Even stars in the galaxy age over the course of millennia. Humans, other animals, and plant life on earth all go through a cycle of life that can be rudimentarily broken into a “growth” phase during our youth, and an “aging” phase that begins between the ages of 30-39 years. 
Aging happens as the body slows its own repair processes, leading to the accumulation of damage to body cells.  Some of these changes are visible—like graying hair and wrinkling skin—but many of them are not. The body’s ability to ward off infection, move freely, and resist wear and tear wanes as humans age, which is why the risk of dying increases exponentially as we reach the end of our current expected lifespans. 
But why do our bodies start to give out on us over time? The answer, it turns out, isn’t a simple one. “Aging is a complex process dictated not only by the number of years lived, but by genetics, environment, and the complicated interaction of both on our bodies,” says Dr. Blander. 
Why can't people live forever?
There are a few primary theories that seek to explain why we age. Some theories of aging maintain that aging is inherent to the life of a cell, and a gradual loss in function over time is programmed into its DNA. 
Other theories place more importance on the role of the environment and lifestyle factors, which interact with our genetics and change the way our DNA is expressed.  Environmental exposure to things like pollution, cigarette smoke, and UV rays increase free radical formation and accelerate cellular aging (think of free radicals like tiny wrecking balls to cells).  Then there’s the “rate of living” theory, which posits that metabolic rate determines lifespan, with a slower metabolism increasing lifespan and a faster one shrinking it. 
Though the expected lifespan is currently around 80 years, some scientists—including Dr. Blander—believe that humans could live upwards of 150 years if we eliminate environmental sources of stress and cellular damage. A 2021 analysis of NHANES and UK Biobank data suggests that the body’s inherent resilience, or capacity to recover from the damaging effects of stressors, has an ultimate limit of 120-150 years that, they propose, dictates the absolute limit of human lifespan. 
Alas, humans (like all living things) cannot live forever. But there may be potential to lengthen human lifespan by addressing the causes of aging and implementing behaviors proven to reduce the risk of early death.
How humans can live a longer life
Here are just a few strategies that show promise in slowing down the aging process and lengthening our lives. More research is needed to understand their full effect on extending the human lifespan.
A growing body of research suggests that a moderate reduction in calorie intake over a long period of time (3-15 years) may help to increase lifespan by slowing down the aging process. [11,12] Calorie restriction is thought to increase the body’s “cellular housekeeping” process, known as autophagy, and increase the efficiency of mitochondria. 
However, there are risks to reducing calorie intake too much. Unabandoned calorie restriction may lead to malnutrition—increasing the loss of lean mass and the risk of illness. [14,15] Reducing energy intake also decreases the body’s metabolic rate and increases the risk of further weight gain down the road. So it’s important that any calorie restriction you undertake feels sustainable for the long term.  Calorie restriction is also probably not the best choice for athletes, as it could lead to an increased risk of injury and hormonal disruptions in both males and females. 
Dietary restriction is a known predictor of binge eating and other eating disorder pathologies, but this does not always show up in experimental settings. [17,18] Results from the 6-month first phase of the CALERIE study encouragingly showed no increase in disordered eating pathologies with a reduction in calorie intake.  However, it's important to remember this is a fairly short-term result for an intervention designed to be continued for life.
A popular alternative to permanently reducing calorie intake, which is likely unsustainable for most people in modern society, is intermittent fasting (IF). There are many different variations of IF. Some people practice whole-day fasts followed by days of unrestricted eating. And then some people choose to adhere to periodized fasting periods where eating is limited to a time-restricted window (under 10 hours) followed by a longer window of fasting for at least 14 hours (but is commonly 16 hours). 
Studies have found that IF produces some of the same anti-aging physiological changes as calorie restriction, like increasing autophagy, even if overall energy intake does not change [21,22]. Interestingly, in experimental settings, the benefits of IF are primarily seen when individuals eat earlier in the day versus later in the evening, which is thought to be correlated with our innate circadian rhythm. [22-24]
Practically speaking, most people can harness the benefits of IF without making substantial lifestyle changes. Eating from a period of 9 AM to 7 PM and fasting in between (while ideally getting 7-8 hours of sleep), can be considered IF.
Though encouraging, IF research in humans is still in its infancy. Many scientists point out that long-term, representative studies are needed to tease out the effects of IF across the population, and IF is not currently recommended for everyone. [25,26]
Anti-aging drugs and therapies
Given the difficulty of long-term lifestyle change for many people, scientists and physicians alike are interested in exploring the potential of pharmaceuticals in longevity. An anti-aging pill may sound like science fiction, but we may not be far off from that reality.
Emerging research suggests that the popular type 2 diabetes medication, metformin, may slow the aging process, though most of these results are seen for individuals with diabetes who take the drug. [27,28]
It’s still not clear exactly what role metformin plays in preventing aging, though many theories exist. [29, 30] Since most research to date has looked at the impact of this medication on type 2 diabetes, not much is known about how taking metformin affects those who are otherwise healthy. Studies like the ongoing TAME study by Dr. Nir Barzilai, are hoping to provide insight into the anti-aging benefits of metformin for those without type 2 diabetes.
There’s also rapamycin—an immunosuppressant medication commonly prescribed to organ transplant patients. Rapamycin inhibits the activity of a signaling pathway in the body that regulates stress, growth, and metabolism and is thought to prevent aging.  There is a small body of research that supports the safety of rapamycin as an anti-aging therapy, however, more research is needed before it is more broadly recommended. 
One theory of aging proposes that our epigenetic age—the degree of methylation that accrues over time in our DNA—has more to do with aging than simply growing older. Scientist and InsideTracker founder Dr. Blander believes that epigenetic aging is related to cellular differentiation, and may be reversible with the help of stem cells.
As we age, the cells in our bodies become more differentiated and suited to specific functions. Stem cells, on the other hand, are also called “undifferentiated” cells, meaning they can develop into any type of cell in the body when needed. Differentiated cells are thought to have a limit to the number of times they can replicate and survive (called cellular senescence).  However, injecting differentiated cells with stem cells appears to reverse the age of the cell, allowing them to continue to replicate far longer. 
Though this suggests that stem cells could theoretically prevent aging, the practical application of this technology is still in development. 
How long will humans be able to live in the future?
Understanding why and how humans age has paved the way for research into longevity and aging prevention. We’re only just beginning to understand what is possible, but InsideTracker founder Dr. Gil Blander believes humans may be able to theoretically live up to 310 years.
“Based on mathematical models, our longest potential [lifespan] is around 150 years,” says Dr. Blander. However, “we know that genetic manipulation of model organisms increases their lifespan by up to 100%, so taking into account point number one [humans] can live up to 244 years.”
But he doesn’t stop there. Instead, he encourages us to look at the work of Steven Austad, who coined the term longevity quotient [LQ] in his book Methuselah's Zoo. Austad’s LQ is based on animal weight. “For example,” Dr. Blander explains, “human LQ is 5.5, while rougheye rockfish LQ is 14.”
“Jeanne Calment, a French woman, achieved an incredible feat of living to age 122,” says Dr. Blander about the longest-living woman in recent history. “Based on that [and Austad’s LQ], we can theoretically live up to 310 years… [and with] stem cell technology, organ regeneration, and other potential future biotechnologies improvements we might live much longer.”
While that all sounds amazing, you might be wondering what you can do to prevent aging now.
For this, Dr. Blander believes in the 80/20 rule. “The 80% are the basics, don't smoke, eat healthy foods, exercise, sleep well, and don't drink too much alcohol.”
Then, “The 20% is all about personalization,” he says. “What your body needs based on diagnostic, personalized wellness. I think we can live with a good healthspan until death. That's what we are doing at InsideTracker. Test your blood, DNA, and data from fitness trackers, fill in a questionnaire, and based on that receive a fully personalized plan for how to live longer and healthier.”