Fasting blood sugar levels and health risks
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Fasting Blood Sugar Levels and All-Cause Mortality Risk
Research consistently shows that both low and high fasting blood sugar (FBS) levels are linked to increased health risks, especially for all-cause mortality. Very low fasting glucose levels (below 4.0 mmol/L or about 72 mg/dL) are associated with higher risks of death, stroke, and major cardiovascular events in people without diabetes or cardiovascular disease . Similarly, in patients with diabetes, a J-shaped relationship is observed, where both low (<80 mg/dL) and high fasting glucose levels increase the risk of death, with the lowest risk found in the 80–100 mg/dL range . In the general population, the lowest mortality risk is typically seen with fasting glucose levels between 80–94 mg/dL, regardless of age or sex . Prediabetes (100–125 mg/dL) is also linked to higher mortality, and the risk associated with high glucose is stronger in younger adults .
Fasting Blood Sugar and Cardiovascular Disease Risk
Elevated fasting blood sugar, even within the high-normal range (95–99 mg/dL), is independently associated with an increased risk of cardiovascular disease (CVD) in people without diabetes Shaye2012Bjørnholt1999. The risk of CVD, ischemic heart disease, myocardial infarction, and thrombotic stroke rises progressively as fasting glucose increases above 100 mg/dL . Both low (<70 mg/dL) and high fasting glucose levels are predictors of stroke and coronary heart disease . In older adults with diabetes, the lowest risk for cardiovascular events is seen with fasting glucose levels between 95–124 mg/dL, and less stringent glucose targets may be safer for those with multiple health conditions .
Fasting Blood Sugar Variability and Health Outcomes
Not only the absolute level but also fluctuations in fasting blood sugar are important. High variability in FBS from visit to visit is linked to a greater risk of microvascular and macrovascular diseases, cardiovascular mortality, and all-cause mortality in both diabetic and non-diabetic individuals . Changes in fasting glucose status, such as moving from normal to impaired or diabetic fasting glucose, are associated with increased risks of myocardial infarction, stroke, and death .
Fasting Blood Sugar and Hypertension Risk
High fasting blood sugar (≥7.0 mmol/L or 126 mg/dL) increases the risk of developing hypertension, even in people without insulin resistance. This risk remains significant after accounting for other factors like age, weight, and lifestyle .
Conclusion
Both low and high fasting blood sugar levels are linked to increased risks of death and cardiovascular events. The safest range for fasting blood sugar appears to be between 80–100 mg/dL for most adults, with slightly higher targets possibly being safer for older adults with multiple health issues. Fluctuations in fasting blood sugar and increases over time also raise health risks. Monitoring and maintaining stable, moderate fasting blood sugar levels is important for reducing the risk of mortality, cardiovascular disease, and hypertension.
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