Metabolic Syndrome: Additional Details
Insulin is a hormone that allows glucose to move into tissue cells, where is it is used for energy production. Insulin then prompts the liver to either store the remaining excess blood glucose as glycogen (for short-term energy storage) and/or to use it to produce fatty acids (which then become triglycerides). In people with insulin resistance, additional insulin must be released by the pancreas to overcome the tissue cells' resistance and allow glucose to enter the cells. This resistance and response to resistance can lead to increased insulin and glucose concentrations in the blood. Over time, increased glucose levels can harm blood vessels and organs such as the kidneys. Increased insulin levels can increase sodium retention by the kidneys, resulting in increases in blood pressure (which can lead to hypertension).
The liver uses triglycerides, cholesterol, and protein to make triglyceride-rich very low-density lipoproteins (VLDL). In the blood, an enzyme removes triglycerides from VLDL to first produce intermediate density lipoproteins (IDL) and then low-density lipoproteins (LDL - the "bad" cholesterol). LDL is not all bad; it is an essential part of lipid metabolism and is necessary for the integrity of cell walls and for sex hormone and steroid production. However, in excess, LDL can oxidize and accumulate, eventually leading to fatty deposits in artery walls and to hardening and scarring of the blood vessels (and to cardiovascular disease and blood clots).
LDL molecules are produced in a variety of sizes. Small dense LDL (sdLDL) are thought to be more prone to have their cholesterol deposited in artery walls than their larger counterparts. In obese and/or insulin-resistant people, excessive amounts of VLDL and triglycerides remain in the blood and lead to increases in the number of sdLDL produced.
High-density lipoprotein (HDL – the "good" cholesterol) ordinarily transports excess cholesterol from the tissues back to the liver. In the liver, the cholesterol is either recycled for future use or excreted into bile. HDL's reverse transport is the only way that cells can get rid of excess cholesterol. It helps protect the arteries and, if there is enough HDL present, it can even reverse the build up of fatty plaques in the arteries. When there are excessive amounts of VLDL and triglyceride present, however, HDL concentrations in the blood decrease.