When a person’s plasma lipid concentration exceeds the upper limit of normal, it is referred to as hyperlipidemia; when plasma lipoprotein levels exceed the upper limit of normal, it is referred to as hyperlipoproteinemia. Since most lipids are transported throughout the body bound to plasma proteins, hyperlipidemia is often reflected as hyperlipoproteinemia.
I. Normal Blood Lipids and Lipoproteins
The major lipid components in plasma include cholesterol, triglycerides, phospholipids, free fatty acids, and trace amounts of steroid hormones and fat-soluble vitamins. Blood lipid levels in healthy Chinese individuals are lower than those in people from Europe and the United States.
Normal fasting blood lipid values (for reference only): Total cholesterol 110–200 mg/dL, with a maximum of 230 mg/dL; triglycerides 20–110 mg/dL, with a maximum of 130 mg/dL; phospholipids 110–210 mg/dL; free fatty acids 200–600 μEq/L.
Blood lipid levels are influenced by various factors: cholesterol and triglycerides increase with age; in women, cholesterol levels are higher than usual before menstruation and during pregnancy; levels often rise temporarily after a high-fat meal; blood cholesterol is often elevated in those who consume large amounts of animal fats or cholesterol-rich foods; and triglyceride levels are often higher in those who consume large amounts of carbohydrates. In addition, various hormones, medications, and other factors can also influence these levels.
With the exception of free fatty acids, which bind to albumin, all other lipids in plasma bind to globulins to form water-soluble lipoproteins, which are then transported throughout the body via the bloodstream. Lipoproteins can be divided into four categories: (1) high-density lipoproteins (HDL), also known as α-lipoproteins; (2) low-density lipoproteins (LDL), also known as β-lipoproteins; (3) very low-density lipoproteins (VLDL), also known as pre-β-lipoproteins; and (4) chylomicrons.
In healthy individuals, cholesterol has two sources: one is exogenous, derived from cholesterol-rich foods such as egg yolks, butter, brain tissue, organ meats (particularly animal liver), and fatty fish and meats; the other is endogenous, synthesized from acetyl-CoA by various tissues within the body, with 90% of this production occurring in the liver and intestinal mucosa. Most of the cholesterol entering the liver from the intestines and tissues is broken down into bile acids within the liver and excreted into the small intestine via the bile ducts with bile. A small portion is broken down into bile salts and excreted in the feces, while the majority is reabsorbed by the liver, forming the enterohepatic circulation.
Sources of triglycerides in the plasma of healthy individuals: First, those derived from the digestion and absorption of food are exogenous and are contained in chylomicrons; second, endogenous triglycerides synthesized in the liver from carbohydrates and other sources, which are contained in pre-β-lipoproteins. After a high-fat meal, the number of chylomicrons in the blood increases, potentially resulting in milky-appearing plasma. This peaks 4 hours after the meal and persists for 8 to 12 hours; in healthy individuals, the plasma clears within 12 to 16 hours. Excessive fat intake leads to exogenous hypertriglyceridemia. Excessive sugar intake, in turn, ultimately leads to endogenous hypertriglyceridemia.
II. Classification by Etiology
Etiology can be divided into two major categories: (1) Primary cases, where the cause is unknown and most are familial; (2) Secondary cases, which are associated with various diseases. The classifications are as follows:
1. Hypercholesterolemia: ① Secondary: diabetes, atherosclerosis, nephrotic syndrome, myxedema; ② Primary: familial hypercholesterolemia.
2. Hypertriglyceridemia: ① Secondary: severe diabetes, atherosclerosis, nephrotic syndrome, chronic pancreatitis, fatty liver, glycogen storage diseases, and pregnancy, among others. ② Primary: idiopathic hypertriglyceridemia.
3. Hyperlipoproteinemia: ① Intra- and extrahepatic biliary tract obstruction caused by various factors, and cholestatic liver and biliary diseases, including intrahepatic canalicular hepatitis. ② Idiopathic biliary cirrhosis.
4. Mixed type: Hypercholesterolemia and hypertriglyceridemia; causes include uncontrolled diabetes, acute pancreatitis, chronic pancreatitis, nephrotic syndrome, alcoholism, and multiple myeloma.
III. Clinical Classification
Hyperlipoproteinemia can be classified into five types based on plasma appearance, lipid profile measurements, and lipoprotein paper electrophoresis:
Type 1: Hyperchylomicronemia, a congenital lipoprotein deficiency that is relatively rare. It is most commonly seen in adolescents, particularly those under 10 years of age, who often experience acute abdominal pain after consuming a high-fat meal. Erythematous xanthomas appear early, accompanied by moderate hepatosplenomegaly, which fluctuates with triglyceride levels; when triglycerides exceed 2000 mg/dL, lipoid retinopathy develops.
Type II: Hyperlipoproteinemia, which is more common. It is characterized by xanthomas on the eyelids and tendons, subcutaneous nodular xanthomas on the elbows, knees, and buttocks, juvenile keratitis, and early-onset (before age 40) atherosclerosis, which progresses relatively rapidly. Cholesterol levels are significantly elevated. Some cases are hereditary, while others may result from a diet high in cholesterol or be secondary to conditions such as multiple myeloma, nephrotic syndrome, and liver disease. Type II is subdivided into subtypes Ia and IIb.
Type III: Both blood cholesterol and triglycerides are elevated. This is less common and follows an autosomal dominant inheritance pattern. It typically presents between the ages of 30 and 40, with the appearance of flat xanthomas and tendon xanthomas, often accompanied by obesity and glucose metabolism abnormalities. It is characterized by early-onset atherosclerosis of the coronary and peripheral arteries, which progresses rapidly.
Type IV: Hyper-pre-β-lipoproteinemia, the most common type, is characterized by cardiogenic elevation of triglycerides associated with carbohydrate metabolism disorders; cholesterol levels are not necessarily elevated. It is most commonly seen after age 20 and is characterized by nodular and rash-like xanthomas in tendons and subcutaneous tissue, eyelid xanthomas, and retinal lipidosis. It is associated with early-onset and rapidly progressing atherosclerosis and may be accompanied by pancreatitis and diabetes.
Type V: A mixed type, combining features of Types I and IV; it is relatively rare and of limited clinical significance.
IV. Diagnosis and Treatment
Key points for diagnosing this condition include noting in the medical history whether there is a family history of the disease, as well as the presence of diabetes, gout, or liver and kidney diseases. During the physical examination, attention should be paid to the presence of xanthomas, xanthelasmas, early-onset corneal rings, and peripheral vascular disease. A diagnosis can then be made based on blood lipid and lipoprotein test results.
In Traditional Chinese Medicine (TCM), this condition falls under the categories of “dizziness” and “phlegm-turbidity,” and is further classified into Liver-Kidney Yin Deficiency and Internal Damp-Heat.
V. TCM Differential Diagnosis and Treatment
1. Liver-Kidney Yin Deficiency: Manifestations include dizziness, lightheadedness, tinnitus, blurred vision, restlessness, forgetfulness, soreness and weakness in the lower back and knees, a red tongue with little coating, and a thin, taut pulse. The treatment principle is to nourish the liver and kidneys, using the Shouwu Yanshou Dan formula with appropriate modifications. If there is hyperactivity of liver yang, manifested by prominent headaches or a sensation of head distension, add Cassia seeds (Jue Ming Zi) and Pueraria root (Ge Gen); for deficiency of qi and blood, add Astragalus (Huang Qi) and Chinese angelica (Dang Gui); for numbness in the limbs, add Gastrodia elata (Tian Ma) and Milettia vine (Ji Xue Teng).
2. Internal Damp-Heat: Manifestations include dizziness, heaviness in the head, headache, irritability with heat sensation and chest tightness, fatigue and lethargy, a bitter taste in the mouth and dry throat, obesity or constipation, a reddish tongue with a yellow, greasy coating, and a slippery pulse. The treatment principle is to clear and drain damp-heat, using Longdan Xiegan Decoction with appropriate modifications.
VI. Prevention of Hyperlipidemia
Many cases of hyperlipidemia result from poor dietary habits or are secondary to conditions such as diabetes; early intervention can help prevent its onset.
According to a traditional Chinese folk remedy, a decoction made from 10 grams each of hawthorn (Shanzha) and Hangzhou chrysanthemum (Hangju), along with 15 grams of cassia seeds (Jue Ming Zi), can be consumed as a tea substitute to treat hyperlipidemia and is also beneficial for hypertension and coronary heart disease.