Science 101

What Does It Really Mean to Be Healthy?

The definition of “health” has changed constantly. Here’s how and what it means today.


In Ancient Egypt and Ancient Greece, health was a matter for the Gods; if a person was healthy it was because they had appropriately sacrificed for any number of deities. It wasn’t until about the 5th century BCE that health became separate from the supernatural thanks to Hippocrates and his theory that disease came from imbalances between bodily fluids. Of course we now know that Hippocrates was way off, but his ideas were crucial for the development of all that came after: the myriad discoveries and scholarship that gave us modern medicine, from the writing of the first anatomy textbook in 300 BCE to the discovery of the cell and microorganisms in the 1600s.

How We Define Health

With each discovery came a revolution in what it means to be healthy. For example, after the 20th century advent of modern vaccines and antibiotics, and more reliable nutrition and public health measures like sanitation, life expectancy skyrocketed as humans could conquer many of the biggest killers of the time: infectious diseases. Since 1900, global life expectancy has more than doubled to around 70 years. In the United States it’s even higher: 78.6 years as of 2017, per the Centers for Disease Control and Prevention (CDC). By 1950, more than three-quarters of deaths in the U.S. were caused by cardiovascular disease and cancer. These two, plus other lifestyle diseases such as diabetes, and stroke, are the main causes of mortality still today.

This shift in what ails us has led to changes in how we measure health itself. Instead of emphasizing say, sanitation and childhood nutrition, public health advice began to include an emphasis on physical fitness, diet and the importance of screening tests, like cholesterol and blood pressure readings and even mammography or colonoscopy results as measures of health. What this shows is that what we consider the “markers” of health depend on a confluence of factors — the cultural context, the contemporaneous burden of disease, and the availability of current medical technology and knowledge to respond to the challenges.  

What this means in practice is that the definition of health is always changing. Today, we are living in the midst of another huge shift in how we define health status. Since 1948, the World Health Organization has defined health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.” But as medical science continues to advance and people continue to live longer and better, scientists and experts have made calls for re-thinking that last requirement. 

The truth is that today, thanks to advances in medical science, you can be very healthy, with your physical, mental, and social well-being on point, well into your golden years. And that’s even if you are living with a disease or a condition that lasts longer than a year and requires ongoing medical attention. More Americans are older than 65 than ever before: 15.6% of the population, according to data from 2018. And some estimates suggest that at least two-thirds of older adults are managing one or more chronic conditions or diseases — defined as conditions that last one year or more and require ongoing medical attention or limit activities of daily living or both, according to the CDC (some examples of diseases include heart disease, cancer, and diabetes while high blood pressure would fall under the definition of condition, not disease). Despite the higher incidence of health conditions among older adults, they still have a greater life expectancy than ever before: People aged 65 today can expect to live another 14 years or so. 

“It used to be that if you said somebody that's 75 or 80 or 85 you would be able to picture pretty much what their health status would be like, but there has been a gradual pivot from a focus on age and diagnosis to a greater appreciation of functional status,” explains John Rowe, M.D., Julius B. Richmond Professor of Health Policy and Aging Health Policy and Management at Columbia University. “An example: if I told you that a man was 77 years old and he had diabetes and a history of heart attack, you could not tell me if that man was in a nursing home or was sitting on the Supreme Court of the United States.”

As growing older and living longer has become not only more common but pretty much expected, there’s been a re-thinking of aging itself; it’s no longer something you just succumb to, but something that’s possible to fight back against. 

“There has been a gradual pivot from a focus on age and diagnosis to a greater appreciation of functional status,” Rowe says. In other words, as people are living longer, it’s becoming clearer by the day that age really is just a number—an increasingly meaningless one. “Now a healthy 80 year old has got a 10 or 15 year life expectancy and so the criterion has shifted from what is your age to what is in fact your active life expectancy,” Rowe says.

A New Way To Measure Health

So how has an aging population changed the definition of health for people of all ages? Aside from creating a more expansive view of what health could mean, it has opened up a new world of research into the aging process itself. 

Aging is “the main risk factor for the prevalent diseases of developed countries: cancer, cardiovascular disease and neurodegeneration,” according to a 2012 review in Cell. Though aging is not a disease, per se, there is a growing awareness that we need to understand more about the process of aging if we’re going to understand these diseases. In fact, just last year WHO added a code for “ageing-related” disease to its 11th revision of the International Classification of Diseases for Mortality and Morbidity Statistics, or ICD-11 — a sign that scientists and medical experts are beginning to agree that aging is being taken more seriously in the disease space. 

What we know now is that aging is a cellular process— well, multiple processes actually. It involves a cascade of various changes, often happening at once happening within your body’s most basic building blocks. So far, scientists have pinpointed at least nine, from mitochondrial dysfunction (when the cellular metabolic engine stops working correctly) and cellular senescence (when cells stop dividing as part of the biological process, but also don’t die off.)

This has added a cutting-edge new dimension to how you can think about your health: In addition to caring about the macro measurements like your blood pressure and weight and simply how you feel, it’s also not a bad idea to consider what’s going on with your health on a micro-level. How is your cellular health

“There has been a search for the holy grail, which is really a measurement that would be a reliable measure of a blood test or some other indirect measure of some body function that would in fact be a better predictor of one's life expectancy and health status than their age,” Rowe says. “Some people think that if you put together a portfolio of biomarkers, from metabolic, immune, inflammatory, musculoskeletal and so on that you could come up with a composite index that would be an important predictor or valuable predictor.” One that’s being considered is DNA methylation, a technique used to better understand how your genes are being expressed based on your lifestyle and environmental factors.

How “Health” Affects Longevity

In the meantime, we do know that the lifestyle choices our doctors encourage us at our annual physicals also promote longevity. In 2018, Harvard researchers identified five main “lifestyle factors” that increase longevity in a study published in the journal Circulation. Using 60 years of data from the National Health and Nutrition Examination Survey (NHANES), they looked at whether people who had never smoked, maintained a low body mass index, exercised 30 minutes a day, and ate a diet high in fruits, vegetables, polyunsaturated fats, and omega-3s, and low in sodium, trans fats and red, or processed meats. In the end, they found that women who ticked all 5 healthy boxes lived 14 years longer than those who didn’t, while men in the same category all lived 12 years longer, compared to those who didn’t.

Beyond those five factors, mental health has also been shown to be important for longevity. In fact, one 2014 study found that a serious mental illness diagnosis can shave as many years off your life as being a pack-a-day smoker can. “Social factors are increasingly important in late life” Rowe adds. “Loneliness is toxic.” One 2018 review found lonely people had a 22% increase in all-cause mortality.

There are also a growing number of novel therapies that may support the quest longevity on a cellular level. One example is supplementation with nicotinamide adenine dinucleotide (NAD+), a coenzyme crucial for healthy cell functioning. NAD+ is known to decline over time, which impacts the healthy functioning of sirtuins, a group of proteins known as “longevity genes.” Similar therapies in the aging space, like cellular senescence, are consistently being studied

In the end, measures of health, whether they’re determined by the Gods or a stethoscope, have always been used to predict longevity. The whole point of knowing your blood pressure numbers or managing your weight is gauging how well you’re doing at delaying disease and ultimately, prolonging the healthy years of your life. As medical science continues to advance, and people continue to live longer, the focus on delaying or even reversing aging itself is going to be a major focus.

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