What are the main components of the circulatory system?

The main components of the circulatory system are the vessels, heart, and blood. The system also includes a person’s blood pressure, as blood pressure involves the blood pumping through the body, and how it affects the heart and blood vessels.

What is a pulse?

A person’s pulse is the alternate expansion and recoil (contraction) of an artery, which can be felt in an artery close to the body’s surface. The pulse occurs because of the rhythmic ejection of blood from the heart into a main artery called the aorta, which causes an increase and decrease of pressure in the artery. The pulse provides important information about the heart action, blood vessels, and circulation. For example, a fast pulse rate may indicate the presence of dehydration. And of course, in a medical emergency, a pulse will help determine whether a person’s heart is pumping.


In general, how does the human heart work?

The human heart (a muscle), located beneath the upper-left portion of a person’s torso, is about the size of a clenched fist. On average, the heart beats about 70 to 75 times per minute (resting) and pumps about five quarts (just over five liters) of blood per minute. Within the heart, two atria receive blood, while two ventricles pump blood out of the heart. The heart also has a natural “pacemaker,” called the sinoatrial node, or the part of the heart that times the contraction by generating and sending electrical signals to what is called the atrioventricular node. The impulses are sent to certain fibers, causing the ventricles to contract. These electrical impulses are also what are detected by an electrocardiogram (EKG) many people receive to check for irregularities in the heartbeat. Several factors can affect the heart’s pacemaker, including two sets of nerves that speed up or slow down the heart, the release of hormones such as adrenaline, and the body’s overall temperature.

Does having diabetes increase the risk of heart disease?

Yes, for most people, diabetes increases the risk of heart disease. In fact, according to the National Institutes of Health, at least 65 percent of people with diabetes die of some form of heart or blood vessel disease. Other research indicates that type 2 diabetes is associated with a two- to fourfold excess risk of cardiovascular disease. This includes such conditions as elevated triglyceride levels and a decrease in HDL (the “good” cholesterol) levels. (For more about triglycerides and cholesterol, see this chapter.)

What is atrial fibrillation?

Atrial fibrillation-often referred to as afib-is the most common abnormal heart rhythm reported. It is estimated that about 1 in 100 people, around 5 in 100 over age 65, and around ten in 100 people over age 80 have this condition. It occurs when the heart beats irregularly in comparison to a normal heartbeat. The symptoms often include heart palpitations, fainting, fatigue, or congestive heart failure. It can also make the blood “pool” within certain heart chambers, causing the heart to “quiver” in a chaotic pattern, which slows the blood flow and creates irregular beats. If the pooled blood stagnates, it can sometimes cause clots to form, which can lead to embolic strokes. Atrial fibrillation is thought of as a problem with the heart’s “electrical control,” mainly a group of cells called the sinus node, also often referred to as the body’s natural pacemaker. If for some reason-and many times, the reasons are difficult to diagnose-the electric signal has a problem, it can cause the heart to pump irregularly.

In atrial fibrilations, the electrical signals sent to the heart muscles are irregular, causing the atria (heart chambers) to not work well together. The resulting, fluttering heartbeat puts people at greater risk of heart attacks.

Are people with diabetes at a higher risk for developing atrial fibrillation?

Some studies indicate that diabetes may be connected to atrial fibrillation (afib). In the past, there was disagreement as to whether diabetes and atrial fibrillation were linked. A study from the Journal of General Internal Medicine published in 2010 indicated that there is a connection, noting that people with diabetes seem to have an almost 40 percent greater risk of developing afib than people without diabetes. The study also found that the risk increases the longer a person has diabetes (with an estimate of afib increasing by 3 percent for each year the person has diabetes) and if the person has uncontrolled blood glucose levels (or if the HbA1c is more than 9 percent). But there is one thing no study has yet found: Which comes first, diabetes or afib?


What are the main types of vessels in the body that transport blood?

The following are the three types of vessels that transport blood throughout the body:

Arteries and arterioles-The arteries and arterioles always transport blood away from the heart (via rhythmic contractions known as the pulse) to the various organs in the body. These vessels are under enormous pressure. Thus, their walls are made of thick and elastic smooth muscles.

Veins and venules-Veins return blood to the heart after it circulates through the body. They are relatively thin-walled vessels that lack muscular tissues but are located within skeletal muscle-which means the blood is propelled upward and back to the heart as the body moves. They also contain one-way “valves” that prevent the backflow of blood within the vein.

Capillaries-The smallest vessels are the capillaries-mostly microscopic vessels that form an elaborate network conveying blood between arteries and veins (the walls are only one cell in thickness). They branch from the ends of small arteries and carry oxygen-rich blood to all tissues of the body-along with allowing for the diffusion of nutrients and wastes between cells and the blood.

What is transcatheter aortic valve replacement?

Transcatheter aortic valve replacement (TAVR) is a surgical procedure for aortic valve stenosis. This is the narrowing of the heart’s aortic valve (one of the main arteries at the top of the heart) that makes the heart muscle work harder, and that can eventually lead to heart failure. People with diabetes are at higher risk of aortic-valve stenosis and have an even higher risk of other cardiovascular complications than others without diabetes.

There are two procedures. One is the aortic valve replacement (AVR), which is usually performed during open-heart surgery (the aortic valve is physically replaced with a mechanical or tissue valve). The other method is the transcatheter aortic valve replacement (TAVR), in which a catheter is inserted with a balloon at the tip. As in a catherization, the catheter is inserted into an artery in the leg, or it can be inserted in a small incision in the chest. The instrument works its way to the damaged aortic valve, and the balloon-which carries a folded tissue or mechanical valve around it-is inflated, pushing the artificial valve into the body’s own valve to fix the problem. TAVR is often used if the patient is at a high risk of complications with AVR as TAVR is a less-invasive procedure than AVR. In more recent studies, it has been shown that the TAVR procedure has a much higher survival rate than the AVR treatment.

What is peripheral artery disease?

Peripheral artery disease, or PAD, is a condition in which the peripheral arteries narrow. The arteries that narrow can include those to the legs (the most common), stomach, arms, and head (brain). It is often caused by atherosclerosis, a disease in which fats, cholesterol, and other substances create plaque that builds up in the peripheral arteries, or the outer regions away from the heart. This buildup causes the arteries to become narrow, reducing or completely blocking the blood flow. The most common symptoms are cramping, pain, or tiredness in the leg or hip muscles during walking (called claudication) or climbing stairs. In many cases, the pain dissipates after resting and returns when the person walks or climbs stairs again. Those most at risk for developing PAD include smokers, people with high blood pressure or high cholesterol, older people, and those who have diabetes.

Is there a connection between peripheral artery disease and diabetes?

Yes, there can be a connection between peripheral artery disease (PAD) and people with diabetes. In fact, if a person has diabetes (either type 1 and type 2), he or she is at a higher risk of developing atherosclerosis, the most common cause of PAD. In addition, PAD most commonly affects the legs and feet, places that may also be affected by diabetic peripheral neuropathy (for more about diabetic peripheral neuropathy, see the chapter “How Diabetes Affects the Nervous System”). PAD (along with diabetic peripheral neuropathy) may lead to pain in the legs (especially during walking), slow-to-heal foot wounds, one foot’s being colder than the other, and, in severe cases, gangrene (in which there is a total loss of circulation), a condition that can increase the risk of foot or leg amputation.

What is the risk that a person with diabetes will develop peripheral artery disease?

It is estimated that a person with type 2 diabetes has a three-times-higher risk of developing PAD than a person without blood glucose problems. If a person has a higher blood glucose level, it means an even higher risk. According to a 2010 study, it is estimated that every one-point increase in a diabetic’s A1c level can increase the risk of having a PAD-related amputation by up to 44 percent for people with type 2 diabetes and 18 percent for people with type 1 diabetes.

How can a person with diabetes lower the risk of peripheral artery disease?

There are several ways a person with diabetes can lower the risk of developing PAD, or peripheral artery disease. The most important, of course, is to monitor blood glucose levels and keep them as balanced as possible, as diabetes promotes the buildup of plaque in the arteries. In addition, exercise can help, as can medications such as statins (especially medicines that help keep the arteries free of plaque).

What are varicose veins?

Varicose veins are enlarged or distended veins, usually occurring in the surface veins of the inside of the thighs and calves of legs. They are caused by the valves inside the veins becoming stretched so they no longer close completely. The affected veins then become filled with blood, often pushing on the skin and appearing as usually bluish or dark purple-colored veins that protrude or bulge through the skin.

Are there any health concerns if a person who has diabetes also has varicose veins?

While varicose veins can be mildly uncomfortable for some, a proliferation of such veins can be accompanied by aching pain, swelling, itching, numbness, or a rash in the legs. In addition, if the veins gradually grow later, they may cause health problems that can require medical treatment. For example, if the pooling of the blood in the vein is significant, it can slow the return of the blood to the heart, possibly causing blood clots and severe infections. And if a varicose vein causes a rash or sore, it could eventually lead to an infection-which is why a person with diabetes and varicose veins should monitor his or her condition closely.

When valves in the veins no longer function properly, the veins get enlarged and distended. Diabetes can compound the problem because of the increased risk of infection it causes.

Can varicose veins occur if a person frequently crosses his or her legs?

Contrary to popular belief, and according to Harvard Medical School, people are not at a higher risk of developing varicose veins if they frequently cross their legs. In fact, heredity is mostly to blame, and it is estimated that more than 80 percent of people are at risk for varicose veins if a parent has the same condition. There are other lesser factors, including high blood pressure, inactivity, smoking, hormonal changes that occur with puberty, pregnancy, and menopause, having a job that requires standing for prolonged periods, and obesity-the last of which often means a person who has type 2 diabetes (for more about obesity, see the chapter “Diabetes and Obesity”).

Are people with diabetes prone to varicose veins?

No, people with diabetes are not prone to varicose veins any more than the general population. But certain conditions may mean a higher risk for people with diabetes. For example, many overweight or obese people with type 2 diabetes have varicose veins, as both are associated with obesity. In addition, because it is estimated that roughly half of people age 50 and up have some degree of varicose veins, and type 2 diabetes is often considered age related, older people may suffer from both conditions.


What is blood pressure?

Blood pressure, as the term implies, is the pressure of the blood in the bloodstream (circulatory system). This pressure rises with each heartbeat and falls when your heart rests between beats and can change from minute to minute, depending, for example, on whether a person is active, sleeping, resting, or under stress. Blood pressure is the lowest in veins and the highest in the arteries when the ventricles of the heart contract. This pumping of blood around the body gives it energy and the oxygen needed to survive. Blood pressure is most often used for diagnosis of certain heart- and blood-related problems in a patient. This is because it is closely related to the force and rate of a person’s heartbeat and the elasticity and diameter of the arterial walls (depending, for example, on whether there is a buildup of plaque in a person’s arteries that would narrow the vessels).

What are the two numbers associated with blood pressure measurements?

Two numbers are associated with blood pressure: the systolic (top number) and diastolic (bottom number). For example, for a reading of 140/90, the top number is the systolic number (the measurement of the pressure when the heart’s ventricles contract as blood pushes through the heart), or 140. The diastolic number (the measurement when the heart relaxes or the pressure maintained by the arteries between heartbeats) is 90. This is often stated as 140/90 mm Hg, or “140 over 90 millimeters mercury,” or how blood pressure is measured by a blood pressure machine. Currently-a much debated topic-the blood pressure for normal resting adults (over age 20) is most often 140/90. These numbers have changed on the basis of new research. In fact, less than a half decade ago, most physicians suggested that a reading of 120/80 was considered healthy (see below about changing blood pressure reading guidelines).

A blood pressure measurement of 120/80 is considered good for healthy adults in their twenties, but older adults may be fine with a reading of 15/90.

What new blood pressure guidelines were recently suggested?

According to the American Heart Association, a blood pressure reading below 120/80 for an adult over age 20 is recommended. But these numbers are currently being debated, and in 2014, the National Institutes of Health changed its blood pressure guidelines for the first time in 11 years. This was based on 2013 research presented in the Journal of the American Medical Association that suggested new guidelines for blood pressure readings depending on age and/or health conditions.

For example, the researchers recommended for the general population an increase from 140/90 to 150/90 mm Hg. It was suggested that among adults age 60 and older with high blood pressure, the goal should be a target blood pressure under 150/90; among adults ages 30 to 59 with high blood pressure, a target blood pressure under 140/90; and among adults with diabetes or chronic kidney disease, a target blood pressure under 140/90. Even though the systolic and diastolic numbers are “higher,” doctors still recommend keeping blood pressure at a healthy low level and, if necessary, to make lifestyle changes to keep it low.

What are hypertension and hypotension?

Hypertension is another way of saying high blood pressure. It is often referred to as a “silent killer.” This is because it usually has no obvious symptoms, meaning not many people are aware they have it. In general, it occurs when a person’s blood is pumping through the heart and blood vessels with too much force. It is usually found when a person has his or her blood pressure taken. If one or both of the numbers in the systolic and diastolic blood pressure measurements are high compared with what is considered normal in the overall human population, it can be an indication of hypertension. Although it is often a debated subject, it is thought that in healthy people, a blood pressure reading of 140/90 is considered normal (this often depends on whether the person’s physician has adopted the new guidelines or not; see above). Hypotension means low blood pressure, in which a systolic pressure is below 100 mm Hg. Most commonly, it is caused by overly aggressive treatment for hypertension.

Why is keeping a healthy blood pressure important to a person with diabetes?

High blood pressure is something a person with diabetes should try to prevent. This is mainly because high blood pressure can damage blood vessels, as does diabetes. Such damage from both conditions can greatly increase the risk of cardiovascular disease and other vascular problems.

What are some risk factors for hypertension?

In the general population, several risk factors are connected to hypertension. For example, severe high blood pressure is three times higher for African Americans versus Caucasians. Older people are at a higher risk for hypertension (it is estimated that almost half of the people age 74 and older have hypertension, whether they have diabetes or not). If you are 35 or older, use oral contraceptives, or smoke, the risk of hypertension is increased. If you are obese or have a body mass index higher than 30 (which is often associated with type 2 diabetes), then the risk for hypertension is greater. And if you have diabetes or kidney disease, the risk of developing hypertension is greatly increased.

Who is affected by hypertension?

High blood pressure can affect any human on the planet. Men, women, and children of all ages and all ethnic origins and races can have high blood pressure. But certain conditions increase a person’s risk of developing hypertension. Some of the most common reasons are obesity, physical inactivity, and an unhealthful diet. High blood pressure has also often been tied to nicotine, salt, caffeine, and alcohol consumption in many studies. In addition, it can be genetic, as it is often common in various families and in certain ethnic groups. If a person’s blood pressure is too high-often from the narrowing of the arteries because of the buildup of fatty deposits on the walls (plaque)-it can cause serious damage to the heart and blood vessels. Such damage can cause the heart to lose its ability to pump well. It can also cause blood vessels to lose their elasticity and ability to carry blood efficiently. High blood pressure also increases the risk of stroke, heart attack, kidney failure, and congestive heart failure.

High blood pressure could lead to a number of serious ailments, from heart disease to even blindness and kidney failure.

Is there a “good” blood pressure reading for people who have diabetes?

The goal for patients with hypertension who do not have diabetes is usually 140/90 or below (not too low, but around that reading). For patients with hypertension and diabetes (or chronic kidney disease), the ideal goal has usually been a blood pressure of 130–135/80 (said as 130–135 [systolic] over 80 [diastolic]) or just below (readings depend on the study). But changes in blood pressure guidelines now propose a maximum target of 140/90.

What percentage of people with diabetes have hypertension?

It is estimated that about 30 percent of people ages 50 and over have hypertension. Depending on the study, it is estimated that 20 to 60 percent of people with diabetes have high blood pressure. Overall, it is known that hypertension often affects people with diabetes. It is not known why there seems to be such a correlation between the two conditions. But it may be a “concurrent” or “simultaneous” effect in which factors associated with both diseases-such as obesity, a high-fat and high-sodium diet, and inactivity-lead to both hypertension and diabetes.

Why are kidney disease, type 1 diabetes, and hypertension linked?

It is thought that hypertension in people with type 1 diabetes may be an indicator of kidney disease. In fact, it is known that hypertension is one of the principal causes of diabetic kidney disease and kidney failure. This occurs as blood vessels are damaged because of tension from high blood pressure. Along with the higher blood pressure, if a person has diabetes, then elevated levels of glucose can also damage blood vessels. And if the person also has high cholesterol, there is an even higher risk of blood-vessel damage. (For more about diabetes and kidney disease, see the chapter “How Diabetes Affects the Urinary System.”)

Does salt affect blood pressure, especially if a person has diabetes?

Most health care professionals agree that, for most people, ingesting too much salt can cause the body to develop high blood pressure over time. In fact, eating too much salt causes the body to hold extra water in order to eliminate the salt from the person’s system. For some people, this causes extra pressure in the blood, causing a rise in blood pressure. The additional water also puts stress on the blood vessels and heart, and when the blood pressure increases, it puts even more pressure on the blood vessels and heart. Thus, the American Heart Association suggests that people with high blood pressure, or a tendency toward developing high blood pressure, should eat foods lower in salt, along with lower amounts of fats and calories. The AHA also recommends that a person ingest no more than 1,500 milligrams of sodium per day. To compare, a teaspoon of salt is about 2,400 milligrams of sodium. (This number has recently been highly debated; for more about the sodium controversy, see the chapter “Diabetes and Nutrition.”)

For a person with diabetes, the effect of salt on blood pressure is also an issue. According to the Joslin Diabetes Center, having diabetes does not mean having to cut salt and sodium from the diet. However, people with diabetes should cut back on their sodium intake since they are more likely to have high blood pressure-a leading cause of heart disease-than people without diabetes.

Consuming too much salt is never a good idea because it affects high blood pressure, which is also an issue with diabetics, of course.

Do some high blood pressure drugs affect the body’s insulin levels?

Yes. Drugs to lower high blood pressure can have different effects on insulin sensitivity in the body. The best way to find out which drugs have such effects is to ask a health care provider about the interactions of certain medications with the body’s insulin. For a person who has prediabetes or diabetes, such questions are necessary, since insulin balance is so crucial to keeping the blood glucose in a healthy balance.

What recent study showed a possible link between the time a person takes his or her high blood pressure medication and type 2 diabetes?

In a recent study, scientists uncovered a possible link between the time when a patient takes blood pressure medication and that person’s risk of developing type 2 diabetes. Unlike people without high blood pressure (hypertension), people with high blood pressure do not experience a drop in blood pressure at night (called “non-dipping”). The researchers monitored people without diabetes, and a certain percentage of them had hypertension. After six years of monitoring the patients, the researchers found that the “non-dippers” were at higher risk of developing type 2 diabetes, while those whose blood pressure dropped at night were at a lower risk. The researchers also did a separate experiment, in which half the participants with high blood pressure took their blood pressure medication in the morning, while the other half took the medication before going to bed. They found that the participants who took their medications at bedtime not only lowered their nighttime blood pressure but also lowered their risk of developing type 2 diabetes by 57 percent compared with those who took the medication in the morning.

Overall, the scientists believe that the connections between type 2 diabetes and blood pressure may be hormonal. For instance, hormones such as adrenaline and angiotensin both contribute to high blood pressure and type 2 diabetes. Thus, for example, when angiotensin is targeted by blood pressure medications and therefore lowered, so is the risk of developing high blood pressure and diabetes. More studies have to be conducted before people change their medications, which is why it is best for a person with diabetes and/or high blood pressure to discuss such possible interactions with a health care professional.

Can high blood pressure be “cured”?

According to most health care researchers, high blood pressure cannot be “cured,” but it can be controlled in many ways. For example, most doctors treat high blood pressure patients with medication and/or through lifestyle modification, with both directed by the health care professional. Overall, a person with diabetes should discuss blood pressure goals with the health care professional.


What are the main components of human blood?

Blood is considered a complex tissue-or group of similar cells-suspended in a fluid medium for easy transport through blood vessels. The following lists the four main components of human blood:

Plasma-Plasma is the liquid portion of the blood, and its principal component is water. Within the water are necessary elements that allow humans to live, especially dissolved salts, nutrients, and gases, along with molecular wastes being removed. It also contains clotting factors, hormones, enzymes, and antibodies.

Red blood cells-The red blood cells-scientific name, erythrocytes-are the most abundant cell type in the blood fluid. These dish-shaped cells measure about 8 micrometers in diameter. They lack a central nucleus like many other types of cells and cannot reproduce. But they have an extremely important job as they carry hemoglobin (a red, oxygen-carrying pigment that, when bound to oxygen, is called oxyhemoglobin) and oxygen throughout the body. These cells only live about 120 days, forming in the bone marrow and being recycled in the liver.

Human blood is composed of plasma, red blood cells, platelets, and white blood cells.

White blood cells-White blood cells are also formed in the bone marrow. They die off fighting infections and are one of the major components of pus.

Platelets-Platelets-scientific name thrombocytes-are small, non-cellular components (actually cell fragments) that form in the bone marrow from megakaryocytes (large bone marrow cells) and are the main reason blood clots so well.

How does human blood clot?

For most humans, the ability of blood to clot is vital. If it couldn’t, then even a small cut could mean bleeding to death. Simply put, blood clotting (or thrombus) involves a mass of protein fibers that trap lymph and red blood cells, eventually hardening into a cap (generally called a scab) that protects the damaged area. The clotting reaction is thought to be platelets in the area of a cut releasing chemicals into the bloodstream, starting the formation of a clot through a series of enzyme-controlled reactions.

What is the connection between blood clotting, arteries, and diabetes?

According to the American Heart Association, diabetes increases the risk of plaque buildup in the arteries, which can cause blood clots. In fact, some studies indicated that a very high percentage of people who have diabetes will eventually die of clot-related causes.


What is blood cholesterol?

Blood cholesterol (or serum blood cholesterol) is a waxy, fatlike substance. Cholesterol is found in all the cells of the human body and helps to maintain the strength and flexibility of the cell membranes (thin layers of the cell). Cholesterol is obtained from food and is also naturally produced by the body. Humans need some cholesterol, but if found in excess levels in the body, cholesterol can often result in an increase in certain diseases, especially heart problems.

Why is there a connection between cardiovascular disease and diabetes?

At this writing, researchers really do not know why there is such a strong relationship between diabetes and cardiovascular disease. This is because the majority of people with diabetes also have other heart disease risk factors, such as high blood pressure, high triglycerides, and obesity (some researchers would add higher levels of LDL, the “bad” cholesterol, and lower levels of HDL, the “good” cholesterol, to the list). But currently, many scientists are debating just how “bad” and “good” the two types of cholesterol are for people and just how much is detrimental.

HDLs are the cholesterols in your blood that help prevent clotting, while LDLs can create blockage.

What are the so-called “good and bad cholesterols”?

There are, according to doctors, “good” and “bad” elements in the human body that can affect the body’s healthy balance, especially in the circulatory system (or in other words, the heart and blood). In particular, if too much LDL, or low-density lipoprotein, often called the “bad” cholesterol, (although it is not a cholesterol; see sidebar) circulates in the blood, it can create a buildup of what is called plaque on the inner walls of the arteries that feed the heart and brain. This in turn can cause the arteries to narrow and become less flexible (in excess, such plaque buildup is called atherosclerosis).

HDL, or what is often called the “good” cholesterol (although, again, it is not a cholesterol) or high-density lipoprotein, is thought to protect the body against heart attacks by carrying blood cholesterol away from the arteries and to the liver, where it is passed from the body. In addition, it may even slow plaque buildup. Yet another player in the body’s cholesterol levels is Lp(a)-a genetic variation of LDL cholesterol. In particular, a high level of Lp(a) may be a high risk factor for the premature formation of fatty deposits in the arteries. Although not much is known about Lp(a) at this time, it may be connected to the buildup of fatty deposits.

What are the suggested cholesterol levels for an adult?

Many factors affect our bodies-and one of them has to do with our cholesterol levels, especially in terms of the heart. The following, from the American Heart Association, lists what is currently thought to be the best cholesterol levels for an adult:

Cholesterol Level Guidelines

Total Cholesterol Level


Less than 200 mg/dL

Desirable level that puts you at lower risk for coronary heart disease. A cholesterol level of 200 mg/dL or higher raises your risk.

200 to 239 mg/dL

Borderline high

240 mg/dL and above

High blood cholesterol. A person with this level has more than twice the risk of coronary heart disease as someone whose cholesterol is below 200 mg/dL.

Why are terms “HDL cholesterol” and “LDL cholesterol” often confusing?

The terms “HDL and LDL cholesterols” are often misnomers. This is because, although they are associated with cholesterol, they are truly not types of cholesterol. In reality, both are fat–protein compounds that transport cholesterol though the blood and thus throughout the body. HDL tends to carry blood cholesterol away from the arteries, and LDL tends to deposit cholesterol on the artery walls. One of the main problems with these terms is easy to see: When the blood cholesterol is attached to a lipoprotein-either HDL or LDL-the entire complex can be referred to as HDL and LDL cholesterol.

What is the connection between atherosclerosis and diabetes?

Atherosclerosis occurs when lipids, particularly cholesterol, build up on the side arterial walls. Risk factors for atherosclerosis include cigarette smoking, a high-fat/high-cholesterol diet, and hypertension. For people who have either type 1 or type 2 diabetes-conditions that include inflammation and slow blood flow-the development of atherosclerosis can be dramatically accelerated.

How do statin drugs work?

Statins are a group of drugs that work to lower cholesterol levels, particularly the “bad cholesterol,” or the low-density lipoprotein known as LDL. The drugs work in two ways: They block an enzyme that is needed for cholesterol production, and they increase LDL receptors in the liver. (Cholesterol can only get into cells by binding to specific receptors that remove the LDL from blood. The extra receptors that statins create help decrease the cholesterol levels.) As Americans are more aware that high cholesterol is a major risk factor for heart disease, statins have become increasingly popular.

What recent study indicated that certain statin drugs can lower the risk of amputation of the extremities, especially for people with diabetes?

Although giving cholesterol-lowering statins to people with type 2 diabetes has been around since 2010, the studies conducted have not been extensive. But a long-term study with close to 17,000 participants conducted in 2016 found that people with PAD (peripheral artery disease)-including many people with diabetes-seem to have a 22 to 33 percent lower risk of leg or other limb amputation when taking statins. The statins, many of them routinely supplied to people who have PAD, apparently lower cholesterol levels enough to cut back on the formation of arterial plaque. For many people with diabetes, the statin dosage has to be high, and if they can tolerate the medication-along with making other lifestyle changes (such as exercising and not smoking)-they can often lower their risk of amputation. (For more about PAD, see this chapter.)

Can statins increase the risk of developing diabetes?

No one really knows, but a study presented in 2015 suggested that statins can increase the risk of developing type 2 diabetes. In particular, the drugs appear to increase a person’s insulin resistance and also impair the ability of the pancreas to secrete insulin. But more research needs to be done, as this study pertained only to the risk of developing diabetes-and was limited to men.

What are triglycerides?

Triglycerides are a type of fat (lipid) found in the blood. When a person consumes a meal or snack, the body converts any of the calories it does not need to use right away into triglycerides. This is stored in the fat cells. If a person needs energy, then certain hormones allow the triglycerides to be released into the bloodstream. Because, like cholesterol, triglycerides cannot dissolve in the blood, they circulate throughout the body with the help of proteins called lipoproteins.

What is dyslipidemia (or dyslipidaemia)?

Dyslipidemia is a condition in which a person has an abnormal amount of lipids (mainly triglycerides), cholesterol, or both. It can also mean the person has high triglycerides, low HDL cholesterol, and often type 2 diabetes. (The most common type is called hyperlipidemia, or elevated lipid levels). Dyslipidemia is divided in two ways by researchers: by phenotype, or the way it is presented in the body (including the specific type of lipid that is increased in the body), and by etiology, or the reason for the condition (such as if it is genetic or secondary to another condition). Because of its connection to fats and to being overweight or obese, dyslipidemia is often associated with people who have type 2 diabetes-and vice versa.