Fasting blood glucose levels
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Fasting Blood Glucose Levels and Health Outcomes
Fasting Blood Glucose and All-Cause Mortality
Research shows that both low and high fasting blood glucose (FBG) levels are linked to increased risk of death. In people without diabetes or cardiovascular disease, FBG levels below 4.0 mmol/L are associated with higher risks of all-cause mortality, major cardiovascular events, and stroke, while slightly higher but still low levels (<4.6 mmol/L) do not show this risk increase . In patients with diabetes on hemodialysis, a J-shaped relationship is observed: the lowest mortality risk is at FBG 80–100 mg/dL, with higher risks at both lower and higher FBG levels . Large-scale studies confirm that the lowest mortality is seen with FBG between 80–94 mg/dL, regardless of sex and age, and that prediabetes (FBG 100–125 mg/dL) is linked to higher mortality, especially in younger adults .
Fasting Blood Glucose and Risk of Type 2 Diabetes
Higher FBG levels within the normal range (even as low as 87 mg/dL or 4.83 mmol/L) independently predict the development of type 2 diabetes in young men. The risk increases further when higher FBG is combined with elevated triglycerides or higher body mass index (BMI) . This suggests that even "normal" FBG levels at the higher end of the range can signal increased diabetes risk, especially when other metabolic risk factors are present.
Fasting Blood Glucose and Hypertension
Higher baseline FBG is also an independent risk factor for developing hypertension. This association holds true for both men and women, and remains significant after adjusting for other risk factors such as age, BMI, and lifestyle habits. Interestingly, glycated hemoglobin (HbA1c) does not show the same predictive value for hypertension as FBG does .
Fasting Blood Glucose and Stroke Risk
There is a positive, non-linear relationship between FBG and stroke risk. The lowest stroke risk is observed when FBG is between 70–100 mg/dL. As FBG increases above this range, the risk of stroke rises, even in people without diabetes . Low FBG (<4.0 mmol/L) is also associated with a higher risk of stroke .
Genetic and Environmental Influences on Fasting Blood Glucose
Genetic variations, particularly in the G6PC2/ABCB11 genomic region, are associated with differences in FBG levels, accounting for about 1% of the total variation in FBG among nondiabetic individuals . Environmental factors also play a role: long-term exposure to fine particulate matter (PM2.5) is linked to higher FBG levels in elderly people, with those who already have diabetes being especially vulnerable .
Fasting Duration and Blood Glucose Measurement
The traditional requirement of at least 8 hours of fasting before measuring blood glucose may not be necessary. Studies show that after just 3 hours of fasting, blood glucose levels are very similar to those measured after 8 hours, suggesting that shorter fasting periods or even random sampling may be sufficient for accurate assessment .
Effects of Prolonged Fasting on Glucose Metabolism
Prolonged fasting (36 hours) leads to lower fasting glucose, insulin, and C-peptide levels, and improves insulin sensitivity in both non-obese and obese individuals, as well as those with type 2 diabetes. However, in non-obese people, prolonged fasting also results in higher glucose levels during an oral glucose tolerance test, indicating a reduced early insulin response .
Conclusion
Fasting blood glucose is a key indicator of metabolic health, with both low and high levels linked to increased risks of mortality, cardiovascular events, stroke, diabetes, and hypertension. The optimal FBG range for lowest health risk appears to be 80–100 mg/dL. Both genetic and environmental factors influence FBG, and even small increases within the normal range can signal higher risk for future disease. Shorter fasting periods may be sufficient for accurate FBG measurement, and interventions to maintain FBG within the optimal range could help reduce the risk of serious health outcomes.
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