Blood sugar levels in healthy adults
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Normal Blood Sugar Levels in Healthy Adults
Research shows that healthy, non-diabetic adults typically have average blood sugar (glucose) levels around 98–99 mg/dL (5.4–5.5 mmol/L), with slightly higher averages (104 mg/dL or 5.8 mmol/L) in those over 60 years old. Most of the time, their glucose levels stay between 70–140 mg/dL (3.9–7.8 mmol/L), with only about 2% of the day above 140 mg/dL and about 1% below 70 mg/dL. Blood sugar levels in healthy adults rarely fall outside the 80–120 mg/dL (4.4–6.7 mmol/L) range under normal conditions, and fasting levels are usually between 5.0–7.2 mmol/L (90–130 mg/dL) before meals, with less than 10 mmol/L (180 mg/dL) after eating 134.
Blood Sugar Variability and Physical Activity
Healthy adults show low blood sugar variability, with a typical coefficient of variation around 17%. Physical activity plays a significant role in maintaining normal blood sugar. Adults with low physical activity are more likely to have abnormal blood glucose, even if they are not overweight. Inactive individuals are almost twice as likely to have abnormal blood sugar compared to those who are active, highlighting the importance of regular exercise for everyone, not just those at risk for diabetes 15.
Cognitive Effects of High-Normal Blood Sugar
Even within the normal range, higher blood sugar levels can have subtle effects on cognitive function. Studies in young healthy adults found that those with higher blood glucose (within 62–117 mg/dL) performed worse on tests of spatial perception. This suggests that even small increases in blood sugar, still considered normal, may impact brain function .
Health Risks of Higher-Normal Blood Sugar
Research indicates that blood sugar levels at the higher end of the normal range are linked to increased risks of cardiovascular disease and mortality, even in people without diabetes. For example, adults with borderline high blood sugar (7.8–11.0 mmol/L or 140–198 mg/dL) have a higher risk of stroke, heart disease, and death compared to those with lower levels. Each 1 mmol/L (18 mg/dL) increase in blood sugar, even within the normal range, is associated with a higher risk of these outcomes .
Conclusion
In healthy adults, normal blood sugar levels are tightly regulated, usually staying between 70–140 mg/dL throughout the day. Regular physical activity helps maintain these healthy levels. However, even blood sugar at the higher end of the normal range can affect cognitive function and increase the risk of heart disease and death. Maintaining blood sugar in the lower part of the normal range and staying physically active are important for long-term health.
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