How old are you?
You will likely answer this question with your chronological age or the number of birthdays you have had. But this answer does not necessarily reflect your biological age, or how old you are internally.
Everyone ages at a different rate. You probably know someone that is running marathons into their seventies or people in their thirties who suffer from daily aches and pains. Two people who are the same chronological age may have very different biological ages and levels of physical health.
Chronological age is the amount of time a person has been alive.  It is calculated using the number of years, months, and days that have passed from their birth to the present date. Chronological age is not influenced by how healthy or unhealthy a lifestyle one is living. It is always a simple computation. You can even find a chronological age calculator if you feel like avoiding mental math.
Chronological age is how people typically define their age and studies commonly measure the risk associated with certain age-related health conditions using chronological age ranges.
What is biological age?
Biological age is the body’s internal age. It reveals the efficiency at which the body is functioning.
Aging occurs when cells in the body gradually accumulate damage and become less able to divide and multiply.  The rate at which this damage occurs depends on many genetic and lifestyle factors, not just how long a person has been alive. Biological age takes into consideration these various factors and can reveal what age a person’s body truly functions at, in relation to what the calendar says.
What impacts biological age?
- Genetics: There are certain variations in genes that either positively or negatively influence age-related traits. However, genetics isn’t the only factor in healthy aging.
- Diet: Diet plays a key role in the rate of aging by impacting inflammation and metabolic health. What you eat either promotes or fights chronic inflammation, which is the root cause of many age-related diseases [3-4].
- Exercise: Staying physically active can significantly influence aging by activating longevity genes and helping maintain a robust immune system, a healthy body weight, and a lower risk of inflammation. 
- Biomarkers: Research shows that some blood biomarkers are strongly correlated with aging, such as fasting blood glucose, LDL (“bad”) cholesterol, vitamin D, cortisol, and hsCRP (an inflammatory marker). Biomarkers are directly affected by nutrition, fitness, and lifestyle choices.
- Sleep: Sleep affects health and longevity by keeping inflammation at bay. Consistent sleep deprivation may potentially increase the production of pro-inflammatory cytokines and hsCRP (markers of inflammation).
How do you determine your biological age?
There are multiple methods used to calculate biological age including blood tests, telomere length, epigenetic clocks, and online surveys.
Research has linked various blood biomarkers with aging. InsideTracker's InnerAge 2.0 calculates biological age by analyzing these biomarkers via a proprietary algorithm to either add or subtract years from a person’s chronological age, calculating their InnerAge.
From there, the InsideTracker provides food, supplement, and lifestyle recommendations for improving biomarkers that indicate they may be aging faster than they should.
Studies show a relationship between telomere length and aging. Telomeres are the structures at the end of chromosomes, and they tend to decrease with age. But dietary and lifestyle factors influence how quickly they shorten. People who follow healthful eating patterns and who exercise more tend to have longer telomeres compared to those with chronic diseases and who lead more sedentary lifestyles. [6-7]
While telomere length is used as a proxy for biological age, the evidence correlating telomere length to age-related diseases is weak and telomere measurement methods are not reliable.
The field of epigenetics examines the ways that our behaviors and environment impact how our genes work. One type of epigenetics called DNA methylation can cause genes to "turn off.” Environmental, lifestyle, and dietary factors as well as the general aging process can all impact DNA methylation. Epigenetic clocks are tools that aim to account for the factors to measure this DNA methylation. 
There are also several online surveys now available that attempt to estimate an individual’s biological age based on responses from a series of questions. These surveys typically ask about chronological age, health history, and lifestyle to determine biological age. However, this method has not been tested for validity and reliability.
Is chronological age or biological age a better indicator of health?
While chronological age is still commonly used in research to determine a person’s risk for certain age-related conditions and diseases, it is not the best indicator of health because everyone’s body ages at different rates.
Biological age, on the other hand, reflects how quickly or slowly a person is aging. It’s used as a metric of health by revealing how well the body is working given the variety of genetic and lifestyle factors that can influence its function. However, the accuracy of a biological calculator age will depend on the measurement tactic used to determine it.
Nonetheless, biological age is an emerging metric you can use to evaluate and optimize your health.
Four tips for healthy aging
1. Eat nutritious foods
A nutritious diet is a key factor in living a long and healthy life, and certain foods may even help slow the aging process. Whole foods like vegetables, fruits, whole grains, beans, nuts, and seeds are loaded with powerful nutrients and compounds that fight inflammation, which is a major cause of cell damage and aging. Strawberries, for example, contain a compound called fisetin, which acts as an antioxidant and has the power to kill off certain cells that promote inflammation. 
In addition to fighting inflammation, eating a whole foods-rich diet supports a healthy weight and improves many of the blood biomarkers correlated with aging. For example, a systematic review and meta-analysis of observational studies found that plant-based vegan and vegetarian diets were associated with reduced levels of total cholesterol, LDL cholesterol, and blood glucose. 
2. Increase physical activity
Exercise helps combat aging in a number of ways. Research shows that aerobic exercise can help fight inflammation and cellular damage by increasing oxygen flow to muscle cells and boosting the productivity of mitochondria, the powerhouse of the cell.  Strength training can also mitigate bone and muscle loss associated with aging and allow individuals to enjoy their favorite activities for longer. A meta-analysis of over 370,000 participants found that resistance training was associated with a 21% lower risk of all-cause mortality and a 40% lower risk when combined with aerobic exercise. 
3. Stress less
Chronic stress can wreak havoc on our health and has been linked to many negative health outcomes including elevated glucose levels, high blood pressure, weakened immune system, and degradation of body tissues, including muscle.  A recent cohort study of over 400 participants found that stress was associated with accelerated biological aging and insulin resistance.  However, the same study found that participants with stronger emotion regulation were able to prevent any significant effect of stress on their biological age.
These findings are in line with other research that has linked a positive mood with longevity and lower mortality risk.  Research shows tools like meditation and mindfulness can be effective ways to reduce stress and its health effects. 
4. Get quality sleep
Getting adequate, quality sleep is integral to living a long, healthy life. Without enough sleep, the body’s ability to repair is diminished. Poor sleep is linked to numerous negative health outcomes like depression, type 2 diabetes, obesity, cardiovascular disease, and ultimately an increased risk of all-cause mortality . One meta-analysis of a combined 1.3 million participants found that short sleep duration (less than six hours) was associated with a 12% greater risk of death than those who sleep between six and nine hours.  Current research suggests aiming for seven to nine hours of quality sleep per night is best to lower disease and mortality risk. [19-20]
- Chronological age refers to how old you are given your birthday whereas biological age aims to calculate how old you are internally.
- Biological age is an emerging way to measure how well or poorly you’re aging internally based on what’s expected for your chronological age.
- Several methods can be used to calculate your biological age, but methods vary in reliability, accessibility, and affordability.
- Lifestyle habits that affect how well you age and your biological age include eating a healthful diet rich in antioxidants, staying physically active, minimizing stress, and sleeping well.
- Marieb, Elaine Nicpon, and Katja Hoehn. Human anatomy & physiology. Pearson Education, 2007.