Insulin is a hormone made by the pancreas and it acts to regulate carbohydrate, fat, and protein metabolism in the body.
Without insulin secreted into the bloodstream from a very small area called the Islets of Langerhans, most cells in our bodies would die due to lack of energy.
This is because insulin transports glucose (sugar), amino acids, and fatty acids into cells, where they are used for energy or stored.
Numerous factors affect insulin secretion, including exercise, diet, stress, insulin resistance, adrenal dysfunction, and genetics.
Low insulin levels are a feature of insulin resistance in which insulin has difficulty reaching its target tissues due to insulin receptor defects or insulin receptor signaling defects.
Insulin resistance is at the heart of many chronic health conditions, including obesity, diabetes, cardiovascular disease, and possibly Alzheimer’s.
It controls how quickly you absorb food after eating as well as regulating fat storage.
When insulin is low, it slows down the absorption of nutrients from your gut (this means that you may not feel full even when you have finished a meal).
With insulin at optimal levels, insulin will help store excess calories as fat, so they are available later on when needed for energy during an activity like exercise or fasting periods such as nighttime sleep.
Insulin works in opposition to glucagon, which is insulin’s antagonistic hormone. Glucagon acts in the liver and other tissues to maintain blood glucose levels by stimulating the release of stored sugar into the bloodstream for use as energy or glycogen storage when insulin levels are low.
Insulin has many effects throughout your whole body, including:
- Increasing cell growth
- Decreasing cell death
- Promoting the storage of glucose, fatty acids, and amino acids inside cells (the major insulin effect)
- Increasing the absorption of sodium and water by your kidneys which can lead to insulin resistance when insulin levels are chronically high
- Insulin also causes your adrenal glands to release their hormones which can make stress response worse
Insulin resistance is associated with higher insulin levels. This combination of insulin resistance and insulin excess has been linked to many chronic diseases such as obesity, diabetes, cardiovascular disease, and Alzheimer’s. (1, 2)
Recent research suggests that insulin resistance may be triggered by an inflammatory response from elevated insulin levels. (3)
In addition, insulin resistance and insulin excess work together to perpetuate chronic inflammation and insulin resistance, leading to other health conditions such as acne, psoriasis, breast cancer, and prostate cancer.
What are the functions of insulin in the body?
The insulin hormone has a variety of functions, but mainly it is responsible for helping cells absorb glucose from the bloodstream. InsInsulin functions like a key, controlling insulin receptors to let glucose (blood sugar) into your cells. (4)
Insulin also has major effects on amino acids, protein and lipid metabolism.
Most notably, insulin lowers the level of glucose in your blood even while you are eating, therefore it is a hormone that summarizes or stores food energy.
It does this by suppressing the breakdown of glycogen (a stored form of glucose) in the liver and directing much of the food energy toward storage as fat.
Insulin also plays a role in your body’s use of protein and lipids, including certain fatty acids. Proteins are often broken down (catabolized) to amino acids or “burned” for energy (oxidized).
Insulin has an influence on both processes, but it favors storage over breakdown and oxidation.
The same is true for lipids: Insulin suppresses the release of fatty acids from fat cells, promoting their storage instead.
However, when glucose levels are high, insulin will allow fat to be released from the fat stores into the bloodstream.
Why Is insulin important?
Insulin is perhaps the most important hormone in the human body. It provides essential structural components and regulates metabolic pathways to ensure an organism’s survival and activity over 24 hours.
The ability of insulin to regulate blood glucose levels makes it extremely important in maintaining energy homeostasis within a cell, particularly neurons, which require continuous combustion for proper function.
Insulin also plays a role in proper neuronal development, helping to promote the growth of dendritic spines and synapse formation. Insulin is also implicated in neuroprotection by maintaining glutamate levels and inhibiting calcium influx through NMDA receptors during periods of excitotoxicity. (5)
Insulin was first discovered as an extract from the pancreas in 1921 by a team of Canadian researchers. It was later identified as the primary regulator of glucose in the body, aiding insulin-dependent diabetes patients since its discovery, and insulin has been used as an effective treatment for these patients ever since.
Insulin also helps to promote healthy development during puberty, skeletal growth and plays a key role in maintaining energy balance.
The reason insulin is involved in many processes within an organism because insulin resistance can lead to diabetes, obesity, and metabolic syndrome. (6)
What Is Insulin Made Up Of?
Insulin is a peptide hormone consisting of 51 amino acid residues and two chains, insulin-A(1-29) and insulin-B(30-51).
The A-chain contains the insulin molecule that is acted upon by insulin receptors on cells, while the B-chain helps with correct folding of the insulin to be used correctly in the body. (7)
Insulin has two ligands, insulin-like growth factor (IGF) and insulin-like growth factor-binding protein 3 (IGFBP3). IGF is a hormone that aids in insulin signaling pathways, while IGFBP3 keeps insulin from binding to IGF receptors.
Insulin receptors are located on the surface of many cells, especially in muscle and fat cells. Insulin receptors are also present in the brain, but they are not insulin-dependent, and insulin cannot cross the blood-brain barrier.
Insulin has many functions because insulin can bind to different parts of insulin receptors on cell membranes depending on receptor density in a wide range of tissues throughout an organism’s body.
Insulin can be thought of as a key to an insulin-locked insulin receptor on muscle and fat cells.
Once insulin is bound correctly to insulin receptors, insulin ‘unlocks’ the cell membrane for glucose and lipid uptake.
Insulin resistance occurs when insulin cannot bind to insulin receptors correctly due to excess adipose in cell membranes or loss of insulin receptors in cell membranes.
This hinders insulin from unlocking the insulin receptor, and glucose uptake cannot occur properly in insulin-resistant adipose cells. In addition, insulin resistance can lead to insulin overproduction by the pancreas as a response to insulin unresponsiveness on peripheral tissue levels.
Insulin resistance can affect insulin signaling pathways that play an important role in neuronal plasticity. Insulin’s ability to cross the blood-brain barrier can be inhibited, leading to insulin resistance to result in insulin insensitivity in the brain.
Insulin insensitivity in the brain can lead to many possible disorders, including hippocampal sclerosis, impaired glucose tolerance, cognitive impairment, and insulin resistance, which is one of the primary causes of Alzheimer’s. (8)
Diabetes and Insulin
Insulin is one of the most important hormones in the human body. Its name comes from its role as insulin and for working with insulin to regulate metabolism or convert food into fuel (glucose) for use by all cells in the body.
There are two major types of diabetes mellitus: type 1 diabetes and type 2 diabetes. Type 1 diabetes occurs when insulin-secreting cells of the pancreas are destroyed.
Without insulin, glucose cannot enter cells and be used for energy.
The result is a potentially fatal condition called “diabetic ketoacidosis,” where high blood sugar levels can cause coma and even death.
Type 2 diabetes is typically insulin resistance, which can also be associated with insulin insufficiency, where the insulin-producing cells cannot keep up with insulin demands by cells in the body.
People at risk of type 2 diabetes are those who are overweight and inactive or obese and inactive (particularly those with abdominal obesity).
Type 2 diabetes accounts for 90-95% of cases of diabetes and typically occurs in adults.
Insulins Role In Weight Gain And Metabolism
Insulin is associated with insulin resistance, but insulin seems to play a role in metabolism as well. Insulin has been shown to increase appetite, and insulin excitation of hunger centers in the brain increases food consumption while conversely, insulin deficiency decreases food consumption.
In addition, insulin inhibits lipolysis, gluconeogenesis, and glycogenesis, which promotes fat storage rather than fat breakdown. (9)
It’s also been shown to increase lipogenesis, gene expression involved in adipogenesis, and insulin resistance in skeletal muscle cells.
Insulin signaling is also associated with the insulin receptor substrate 1 (IRS1), insulin receptor substrate 2 (IRS2), and phosphoinositide 3-kinase(PI3K).
IRS1 plays a role in insulin pathways by insulin binding to insulin receptors on the surface of IRS1. PI3K and insulin receptor proteins play a role in insulin receptor signaling pathways that initiate insulin’s metabolic effects, enhance insulin resistance and promote obesity, thus making insulin the key player in growth hormone production as well.
IRS2 prevents inflammation caused by pro-inflammatory cytokines like IL-1B and TNF alpha and insulin resistance in adipose cells. Insulin signaling also inhibits insulin-like growth factor 1 production, and insulin receptor activation of phosphatidylinositol 3-kinase plays a role in insulin regulation of glucose transport.
Insulin is not just for energy storage, but insulin plays an important role in insulin resistance and obesity.
Insulin plays a role in insulin resistance from the insulin signaling pathways to insulin receptor activation of IRS proteins via phosphatidylinositol 3-kinase.
Insulin’s Role In Cardiovascular Health And Vascular Function
In order for blood vessels to expand when needed, insulin is necessary because vasodilation (where blood vessels dilate to allow for increased blood flow) is insulin-dependent, and insulin signaling has also been shown to increase nitric oxide, which relaxes the smooth muscles of blood vessels.
Insulin receptor activation plays a role in insulin’s effect on vascular function. Insulin resistance can lead to insulin insensitivity which results in impaired vasodilation.
In resistance, vasodilation is very impaired, and blood vessels cannot relax in response to hypoxia. This lack of a mechanism to increase blood flow can lead to dangerous health conditions, including heart attacks and strokes.
Diabetes is a chronic condition that can lead to insulin resistance, insulin insufficiency, and other health complications.
The insulin hormone plays an important role in the body’s ability to regulate blood sugar levels. Insulin also has effects on immune function, metabolism, vascular function, and cardiovascular health. Insulin resistance leads to impaired vasodilation, which can lead to heart attacks or strokes.
Insulin is also associated with obesity and insulin resistance, leading to type 2 diabetes or just insulin insufficiency.
Each of these health conditions related to the effects of insulin requires medical intervention in order for each patient affected by it to achieve optimal metabolic function.
There are several different ways to treat this condition, from weight control, dietary changes, exercise, and many different drugs.