Hemoglobin A1c (HbA1c or sometimes A1c) is a blood test that measures your average blood sugar levels over the last three to four months. Physicians typically order this test to monitor people who may be at risk of prediabetes or to see how someone is managing diabetes. But more and more people are interested in knowing their HbA1c even if they’re not at risk for metabolic conditions. Data continue to show that optimal blood sugar levels are linked to gut health, cognitive function, and metabolism, whereas chronically elevated levels threaten to shorten a person’s healthspan.
InsideTracker’s personal health analysis offers HbA1c insights as part of the Ultimate, InnerAge 2.0, and Blood Results Upload plans. While an InsideTracker analysis gives you specific insights as to what your HbA1c levels are, here’s an overview of what HbA1c testing can reveal about your health.
A quick overview of blood sugar
Blood sugar, or glucose, is the main type of sugar and energy source for the body. All carbohydrate-containing foods (think breads, cereals, fruits, and vegetables) are eventually broken down to glucose in the body to either be used for energy or stored until needed. Sleep, stress, and exercise alter how the body uses energy—therefore altering blood glucose levels—and blood sugar levels fluctuate readily throughout the day. 
Glucose levels are more commonly measured than HbA1c levels either through a fasted blood test (no food for 12 hours prior) or with a continuous glucose monitor. When blood glucose is measured, it’s only indicative of what your blood sugar is at that point in time. It’s not a comprehensive measure of what your blood sugar levels have been over time. And that’s where HbA1c comes in.
What is a HbA1c test?
A HbA1c test is another way to measure your blood sugar levels. Also referred to as glycated hemoglobin, HbA1c represents the percentage of hemoglobin bound to sugar in the bloodstream over the last three months. Because of this, it’s a much more stable indicator of blood sugar status than a fasted glucose measure.
The science behind hemoglobin A1c
Red blood cells contain a protein called hemoglobin. When glucose is abundant in the blood, it attaches to the hemoglobin through a process called glycation. Once hemoglobin becomes glycated, the hemoglobin molecule stays that way for the remainder of its lifespan of 90-120 days.
So a higher HbA1c level means that more blood cells are glycated and is linked to higher average glucose levels throughout the day. After a meal, blood sugar naturally increases, and the pancreas releases insulin to store glucose in areas outside of the blood cell. If the pancreas is constantly releasing insulin due to chronically high blood sugar levels, then cells may become resistant to insulin, and glucose is never moved out of the bloodstream. Higher amounts of glucose in the blood mean that more cells become glycated over time.
Because glucose is the main source of fuel for cells, altered regulation of this nutrient can have a significant impact on the body. Therefore, hemoglobin A1c level is an output that helps measure metabolic health status.
How is HbA1c measured?
Hemoglobin A1c is most accurately measured by taking a blood sample, though some continuous glucose monitors (CGMs) may offer an estimation based on mean glucose concentration. While a CGM can directly measure glucose, the estimated A1c is calculated by using a formula that associates population level glucose with corresponding hemoglobin A1c direct measurements. The CGM then estimates what HbA1c% is likely to be based on closely correlated direct A1c values.
Numerous studies have been conducted surrounding the accuracy of estimated A1c, concluding that the name “estimated A1c” and its formula is misleading, and now refer to this estimation as Glucose Management Indicator (GMI).  Although this may serve as an approximate measurement for diabetic patients, directly measured A1c is a stronger indicator of metabolic health compared to an estimation from population level statistics.
Who would benefit from a HbA1c test?
Hemoglobin A1c has historically been used as an indicator for managing high blood sugar. However, the benefits of monitoring this marker outside of a clinical setting are rarely discussed.
The Centers for Disease Control and Prevention estimates that 96 million Americans are at risk for developing diabetes and recommends that all individuals test their HbA1c at age 45 or older. [3, 4] However, you don’t need to wait to get an A1c test if you want to proactively take charge of your health. Regular tests reveal a valuable HbA1c trend over time, so you can be sure that you’re taking the right steps for your wellbeing.
You can talk with your doctor about having your HbA1c measured as part of your yearly preventative screening tests, or you can opt for an option like InsideTracker that allows you to test HbA1c (along with other metabolic-related biomarkers) when you want.
What your HbA1c results mean
Hemoglobin A1c results are reported as a percentage, indicating the portion of glycated cells out of the total number of red blood cells in a sample. While exact ranges vary depending on the lab and institution, the American Diabetes Association categorizes results as: 
- Normal: below 5.7%
- Pre-diabetes: 5.7-6.5%
- Diabetes: over 6.5%
How HbA1c levels correlate with fasting glucose
HbA1c levels correlate to glucose levels over the length of a red blood cell’s lifespan. Although many sources demonstrate the relationship between HbA1c levels and glucose, they typically represent blood values for people with diabetes or prediabetes. Average fasting glucose levels increase as Hemoglobin A1c increases: 
|HbA1c||Average fasting glucose (mg/dL)|
Analysis of InsideTracker customer data also shows similar trends within the normal range for HbA1c levels.
|InsideTracker customer’s average fasting glucose for HbA1c levels|
|HbA1c||Average fasting glucose (mg/dL)|
This data show glucose levels continue to increase alongside HbA1c levels, though not significantly.
The impact of HbA1c levels on health
HbA1c is a valuable indicator of glucose metabolism, and therefore overall health due to its impact on several lifestyle categories. Normal HbA1c levels play a key role in healthspan categories such as metabolism, cognition, sleep, and gut health.
Metabolism and energy
Metabolism, or the rate that your body breaks down and uses macronutrients, is associated with HbA1c levels in terms of energy. Because blood glucose is the main fuel for all cells, altering this naturally impacts all metabolic processes. When HbA1c levels rise above a certain threshold, blood glucose levels also tend to be high. Chronically high glucose levels signal the kidneys to release excess glucose in the urine due to dehydration. This ultimately results in a depleted source of energy for metabolism. This dysregulation can result in feeling “brain fog”, irritability, and energy crashes throughout the day. 
Research indicates that 50-70% of people with diabetes report sleep disorders, and HbA1c is significantly associated with poor Pittsburgh Sleep Quality Index (PSQI) and Epworth Sleepiness Scale) scores [8, 9]. For type 2 diabetes, researchers understand a bidirectional relationship between sleep disorders and diagnosis. In some cases, poor sleep can lead to diabetes, while diabetes can also lead to poor sleep [10-12]. Sleep quality is becoming increasingly recognized as a risk factor for chronic disease and quality of life.
Those feelings of brain fog can then have a long-term impact. People with diabetes are twice as likely to develop a cognitive disorder such as Alzheimer’s disease compared to those with normal HbA1c levels.  Higher levels of hemoglobin A1c specifically are associated with poor cognitive performance, especially in aging populations [13,14].
A growing body of research supports a relationship between gut microbiota, glucose homeostasis, and insulin resistance.  Evidence suggests that individuals with higher HbA1c are more likely to experience digestive problems, such as gastroparesis, diarrhea, constipation, and gastroesophageal reflux disease (GERD). This is largely due to nerve damage caused by chronically high glucose levels.
Ways to improve your HbA1c
Whether your hemoglobin A1c is high or normal right now, incorporating sustainable diet and lifestyle habits is the key to healthy blood sugar levels.
Eat a high-quality diet
At mealtime, choose a variety of high-quality and nutrient-dense foods. Pairing a fibrous source of carbohydrates (whole grains, fruits, or vegetables) with a protein and fat source can reduce glycemic response. This means that your blood sugar is less likely to spike and your body will not need to produce as much insulin, lessening the risk for insulin resistance.
Try snacking on an apple with nut butter, eating a mixed-greens salad with protein (chicken or fish), or making brown rice and beans for dinner.
Regular aerobic exercise or resistance training is known for improving blood sugar control and insulin sensitivity. The American Heart Association recommends aiming for 150 minutes per week of exercise, or at minimum reducing the amount of time spent sitting or at rest. Even taking time throughout the day to ensure you’re moving regularly, stretching, or standing can make a difference. 
Keep your stress levels at check
Taking even 5 minutes a day to practice mindfulness, breathing, or meditation can reduce cortisol and blood sugar levels. 
Learn what your HbA1c levels are and track changes overtime
Optimizing your blood sugar levels leads to a range of health benefits and extends your healthspan by lessening your risk for age-related conditions. While measuring this biomarker is still often limited in a clinical setting to those at risk of or those who have prediabetes or diabetes, all adults benefit from knowing where their HbA1c levels stand.
InsideTracker plans offer a convenient solution to measuring this marker and seeing how your levels relate to the different healthspan categories. Depending on whether your levels are optimized or not, you’ll also see science-backed recommendations for how to improve your levels with food, supplements, and lifestyle habits.
Since HbA1c remains relatively stable over three to four months, it can take that long to see noticeable changes in the value after implementing lifestyle recommendations. Getting your HbA1c measured two to four times a year offers a comprehensive insight into your long-term blood sugar control and how different habits throughout the year impact your glycemic response.
 Buettner, Dan. He Blue Zones Solution: Eating and Living Like the World's Healthiest People. National Geographic Society, 2015.