Growing older is unquestionably the greatest risk factor for insulin resistance, prediabetes, and diabetes.¹ However, does aging cause changes in blood glucose levels and, ultimately, type 2 diabetes? This is still being debated.² 

While a small percentage of people are at a higher risk of having problems with glucose metabolism, the vast majority of people can avoid or at least delay the onset of type 2 diabetes.³ This is important because having diabetes speeds up the aging process. The relationship between aging, insulin sensitivity, and type 2 diabetes is complex, involving a number of factors such as body composition, family history, and comorbid diseases.¹

How Is Diabetes Diagnosed?

According to the Centers for Disease Control and Prevention, diabetes affects 27.3 million Americans. This represents approximately 11.3% of the population. One in every five people with diabetes is unaware that they have the disease. An additional 96 million U.S. adults have prediabetes.⁴ 

Adult blood glucose targets are standardized and do not change with age. However, because age is a significant risk factor for diabetes, knowing your blood glucose is critical to understanding your risk for type 2 diabetes. 

According to the American Diabetes Association and the World Health Organization, diabetes is diagnosed when you meet one of the following criteria:¹ 

• Random plasma glucose ≥200 mg/dL (11.1 mmol/L)
• Fasting plasma glucose ≥126 mg/dL (7 mmol/L)
• 2-hour plasma glucose post-75 gram oral glucose tolerance test (OGTT) ≥200 mg/dL (11.1 mmol/L)
• Hemoglobin A1C  ≥6.5%.

Prediabetes is diagnosed when your blood glucose is higher than it should be but does not meet the criteria for diabetes. It is an intermediate stage between having normal glucose tolerance and full-blown type 2 diabetes. Identifying prediabetes and making changes if you have any modifiable risk factors can prevent or at least delay the progression to type 2 diabetes. 

The criteria for prediabetes include:⁵ 

• Fasting blood glucose between 100 mg/dL and 125 mg/dL
• 2-hour plasma glucose post-75 gram OGTT between 140 mg/dL and 199 mg/dL
• Hemoglobin A1C between 5.7% and 6.4%

The Centers for Disease Control and Prevention also offer a Prediabetes Risk Test you can take to get a better understanding of your risk factors.⁶

An isolated fasting blood glucose  misses many older adults with type 2 diabetes. When 1,152 adults were tested using a hemoglobin A1C, fasting plasma glucose, and a 2-hour OGTT, 131 were diagnosed with type 2 diabetes: 

• A fasting plasma glucose test only identified 40 (31%)
• A 2-hour OGTT identified 89 (68%)
• A hemoglobin A1C identified 66 (50%)

Each of these tests identifies a subset of the population, but no single test can identify everyone with type 2 diabetes.¹ Knowing your level of risk for insulin resistance and type 2 diabetes can help you determine how often you should check your blood glucose. 

Another study found that hemoglobin A1C levels rise with age, regardless of age-related increases in insulin resistance, diabetes and prediabetes prevalence, or glucose levels. The cause of the increase in hemoglobin A1C is unknown, but it could be related to glycation or red blood cell lifespan. This means that using age-independent reference values for hemoglobin A1C in older adults may significantly overdiagnose prediabetes and diabetes. Researchers emphasize the importance of monitoring glucose levels in addition to hemoglobin A1C. ⁷ 

Normal Blood Sugar Levels for Adults with and Without Diabetes

Normal blood sugar levels for people without diabetes differ slightly from those with diabetes. Older adults with diabetes are at an increased risk of hypoglycemia (low blood sugar).

Low blood sugar can increase the risk of:⁸ 

• Falling
• Confusion
• Cardiovascular events such as heart attacks and chest pain
• Cognitive function declines
• Fatigue
• Dizziness

For this reason, older adults, especially people with medical problems, have slightly wider target ranges for blood glucose to reduce the risk of hypoglycemia. 

Target Blood Sugar Ranges for Adults^8,9

Adults without diabetes

• Fasting blood sugar: 70—99 mg/dL
• Before eating: 80—130 mg/dL
• 1-2 hours after eating: 80—140 mg/dL
• Bedtime target: 100—140 mg/dL
• Target hgA1C: Below 5.7%

Healthy adults with diabetes

• Fasting blood sugar: Less than 100 mg/dL
• Before eating: 80—130 mg/dL
• 1-2 hours after eating: 80—180 mg/dL
• Bedtime target: 100—140 mg/dL
• Target hgA1C: 7% or less

Older, healthy adults with diabetes

• Fasting blood sugar: 90—130 mg/dL
• Bedtime target: 90—150 mg/dL
• Target hgA1C: 7.5% or less

Adults with complex health problems

• Fasting blood sugar: 90—150 mg/dL
• Bedtime target: 100-180 mg/dL
• Target hgA1C: 7.5% or less

Adults with very poor health and complex medical problems

• Fasting blood sugar: 100—180 mg/dL
• Bedtime target: 110—200 mg/dL
• Target hgA1C: 8.5% or less

<p class="pro-tip">Read more about average blood sugar levels for people without diabetes.</p>