Normal fasting insulin levels
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Understanding Normal Fasting Insulin Levels
Definition and Importance of Fasting Insulin Levels
Fasting insulin levels are a critical measure in understanding an individual's metabolic health. Insulin, a hormone produced by the pancreas, plays a vital role in regulating blood glucose levels. Normal fasting insulin levels are essential for maintaining glucose homeostasis and preventing metabolic disorders such as type 2 diabetes and insulin resistance.
Normal Fasting Insulin Levels and Their Implications
Normal Ranges and Risk Factors
Normal fasting plasma glucose levels are defined as less than 100 mg per deciliter (5.55 mmol per liter) 1. However, even within this normal range, higher fasting plasma glucose levels can independently predict the risk of developing type 2 diabetes, especially in young adults 1. For instance, men with fasting plasma glucose levels of 87 mg per deciliter (4.83 mmol per liter) or more have a progressively increased risk of type 2 diabetes compared to those with lower levels 1.
Insulin Sensitivity and Secretion
Higher fasting free fatty acid (FFA) levels are associated with lower insulin secretion in both children and adults, which can lead to a higher incidence of type 2 diabetes 5. This relationship underscores the importance of maintaining normal fasting insulin levels to ensure proper insulin secretion and sensitivity.
Basal Insulin and Cardiovascular Outcomes
The provision of sufficient basal insulin to normalize fasting plasma glucose levels may reduce cardiovascular events. However, studies have shown that targeting normal fasting plasma glucose levels with insulin glargine had a neutral effect on cardiovascular outcomes and cancers, although it did reduce new-onset diabetes 3. This indicates that while normalizing fasting glucose is beneficial, it must be balanced with the risk of hypoglycemia and weight gain.
Factors Influencing Fasting Insulin Levels
Obesity and Insulin Resistance
Obesity is a significant factor that elevates basal insulin levels, which in turn predicts the magnitude of the insulin response to glucose ingestion 9. Elevated fasting insulin levels in obese individuals are often associated with insulin resistance and beta-cell dysfunction, which can lead to impaired glucose tolerance and type 2 diabetes 10.
Age and Metabolic Deterioration
The process of glucose metabolism deterioration advances with age. More than half of prediabetics have impaired fasting glucose levels but normal postprandial glucose levels, indicating that fasting insulin levels can be a crucial early marker for metabolic disorders 2.
Prolonged Fasting and Insulin Sensitivity
Prolonged fasting increases fasting FFA levels, which can reduce insulin sensitivity and the acute insulin response. However, the use of antilipolytic agents like acipimox during prolonged fasting can partially reverse these effects, suggesting that managing FFA levels is important for maintaining normal fasting insulin levels 4.
Clinical Implications and Management
Screening and Early Detection
Normal fasting plasma glucose levels can help identify individuals at increased risk for diabetes, especially when combined with other factors like body-mass index and triglyceride levels 1. Regular monitoring of fasting insulin levels can aid in early detection and intervention, potentially preventing the progression to type 2 diabetes.
Treatment and Lifestyle Management
For individuals with high normal fasting glucose levels, lifestyle interventions such as diet and exercise are crucial. In some cases, pharmacological treatments like GLP-1 (7-36 amide) can effectively normalize fasting plasma glucose levels in poorly controlled type 2 diabetic patients 6.
Conclusion
Normal fasting insulin levels are a vital indicator of metabolic health. Maintaining these levels within the normal range is essential for preventing insulin resistance, type 2 diabetes, and associated cardiovascular risks. Regular monitoring and early intervention, combined with lifestyle modifications, can significantly improve metabolic outcomes and overall health.
Sources and full results
Most relevant research papers on this topic
Normal fasting plasma glucose levels and type 2 diabetes in young men.
Higher fasting plasma glucose levels within the normal range are an independent risk factor for type 2 diabetes in young men, and may help identify seemingly healthy men at increased risk for diabetes.
Observational Study
Highly CitedJoint analysis of fasting and postprandial plasma glucose and insulin concentrations in Venezuelan women.
Venezuelan women with impaired glucose metabolism can be categorized into prediabetics and diabetics, allowing more specific treatment and predicting metabolic disorder progression.
Observational StudyBasal insulin and cardiovascular and other outcomes in dysglycemia.
Insulin glargine had a neutral effect on cardiovascular outcomes and cancers, but reduced new-onset diabetes and increased hypoglycemia, while modestly increasing weight.
RCT
Large Human TrialHighly CitedEffects of prolonged fasting and sustained lipolysis on insulin secretion and insulin sensitivity in normal subjects.
A 24-hour fast increases free fatty acid levels and reduces insulin sensitivity, but acipimox during the fast partially reverses these effects.
RCTHigher fasting plasma free fatty acid levels are associated with lower insulin secretion in children and adults and a higher incidence of type 2 diabetes.
Higher fasting free fatty acid levels are associated with lower insulin secretion in children and adults with normal glucose tolerance and a higher risk of impaired glucose tolerance and type 2 diabetes.
Observational StudyHighly CitedNormalization of fasting hyperglycaemia by exogenous glucagon-like peptide 1 (7-36 amide) in Type 2 (non-insulin-dependent) diabetic patients
Exogenous GLP-1 (7-36 amide) effectively normalizes fasting plasma glucose concentrations in poorly-controlled Type 2 diabetic patients, maintaining glucose-dependence of its insulinotropic actions.
RCTHighly CitedHow good a marker is insulin level for insulin resistance?
In population studies, only fasting insulin levels should be used as a marker of insulin resistance, particularly in subjects with abnormal glucose tolerance.
Observational StudyHighly CitedMean basal insulin dose is 0.2 U/kg/d at near normal glycaemia for type 1 or 2 diabetes on continuous subcutaneous insulin infusion or once‐nightly basal insulin
A small total basal dose (TBD) is necessary to achieve near-normal basal glucose control in type 1 or 2 diabetes patients when meal-related hyperglycemia is minimized.
Non-RCT
Rigorous JournalThe significance of basal insulin levels in the evaluation of the insulin response to glucose in diabetic and nondiabetic subjects.
Obesity is associated with elevated basal insulin levels, which predict the magnitude of the insulin response to glucose ingestion, while diabetes does not.
Observational StudyHighly CitedHigh normal fasting glucose level in obese youth: a marker for insulin resistance and beta cell dysregulation
Normal fasting plasma glucose levels in obese youth decline from low to high, indicating a risk for insulin resistance and beta cell dysfunction, potentially identifying children for targeted diabetes screening and lifestyle management.
Observational StudyRigorous Journal