Vascular disease affects the circulatory system, the body’s network of arteries, veins and capillaries that carries nutrients and oxygen to the tissues and removes carbon dioxide and other wastes. The cardiovascular system includes both the heart and blood vessels, including the loop through the lungs. The primary vascular disorder is atherosclerosis—hardening of the arteries in the heart, brain and other organs.
How the vascular system functions contributes greatly to the development of chronic conditions such as atherosclerosis, high blood cholesterol, diabetes and high blood pressure. The endothelial cells lining the arteries are active in maintaining normal blood vessel tone—the tension in the walls of arteries—and the chemical, growth and immunological processes that occur in the blood vessels. Smooth muscle cells in the walls of the arteries also regulate blood pressure and contribute to vascular function (Figure 1).
In vascular disease, atherosclerosis causes the artery walls to thicken and narrow, making the blood vessels susceptible to blockage and decreasing their flexibility. If platelets, small blood cells that trigger blood clotting, form a clot where the blood vessel narrows or branches, blood flow is reduced or prevented. If a blood vessel is blocked, a heart attack or stroke follows. With reduced circulation, blood flow in the veins leading to the heart may back up, causing fluid to build up in other parts of the body. Figure 2 shows how plaque builds up in a normal artery to narrow it and decrease blood flow.
The atherosclerosis disease process includes the binding of cholesterol-rich lipoproteins in the inner lining of the artery (endothelium), inflammation of the artery, formation of foam cells that lead to plaque formation and calcification of the arterial wall. Atherosclerosis is generally accepted as an inflammatory disease. Vascular disease that affects the heart is commonly known as coronary heart disease, that affecting the brain as cerebrovascular disease and that affecting the limbs (principally the legs) as peripheral vascular disease.
What health conditions are associated with vascular disease?
Many vascular disorders are associated with the atherosclerotic buildup of plaque, which is formed from cholesterol, fat, calcium and other substances in the blood.
- Aneurysm—balloon-like bulge in an artery
- Angina—chest pain that occurs when an area of the heart muscle doesn’t get enough oxygen-rich blood
- Arrhythmia—an abnormal rate or pattern of heartbeats
- Atherosclerosis—hardening and narrowing of the arteries as a result of plaque buildup
- Cerebrovascular disease—disorders of the blood vessels supplying the brain
- Coronary heart disease—failure of coronary circulation to supply adequate circulation to the heart muscle and surrounding tissue
- Heart attack—also called myocardial infarction, occurs when blood flow to a section< of the heart muscle becomes blocked; if blood flow is not restored quickly, that section of the heart muscle begins to die from lack of oxygen
- Hypertension—abnormally high blood pressure (a reading of 140/90 mm Hg or greater); normal blood pressure is 120/80 mm Hg or lower, with intermediate values considered prehypertension
- Peripheral artery disease—plaque buildup in arteries carrying blood to the head, organs and limbs
- Stroke—occurs when a blood clot clogs a blood vessel in the brain (ischemic stroke) or when a blood vessel breaks and bleeds into the brain (hemorrhagic stroke)
- Venous blood clots—when an atherosclerotic plaque cracks or breaks, platelets clump together at the site to form blood clots that can travel to the arteries or veins in the brain, heart, kidneys, lungs and limbs
What factors influence the development of vascular disease?
Atherosclerosis is by far the most common cause of vascular disease. The long-held view underlying vascular disease risk told us that consumption of total fat, saturated fat and dietary cholesterol raised total and low-density lipoprotein cholesterol (bad cholesterol) levels in the blood, thereby causing cardiovascular disease. But the famous Framingham Heart Study showed there are many factors affecting the chance of developing heart disease, stroke and vascular disease—including smoking, stress, unhealthy diet, lack of exercise, high blood pressure, high blood cholesterol, low levels of high-density lipoprotein cholesterol (good cholesterol), diabetes, advancing age, being overweight, family history of premature heart disease, high blood triglycerides and others. Dietary habits contribute to many of these factors and can be effective in reducing their contribution to vascular disease. In particular, the quality of fat we eat, including the omega-3 fatty acids from fish, can reduce the impact of several of these factors.
HOW DO WE KNOW THAT LONG-CHAIN OMEGA-3 FATTY ACIDS AFFECT VASCULAR HEALTH?
Early observations on diet and vascular disease
Over two decades ago, investigators reported that deaths from coronary heart disease were more than 50 percent lower among people who consumed at least 30 grams of fish per day than among those who did not eat fish. Even before that, it was known that native Arctic populations, whose diet was rich in sea animals, were free of heart disease, thanks in part to the long-chain omega-3 fatty acids (omega-3s) they consumed. Population studies and clinical trials indicated that dietary fish oils favorably modified various risk factors and had the potential to reduce vascular disease progression, the chance of dying from heart disease and the possibility of sudden cardiac death. In elderly individuals, eating tuna or other broiled or baked fish was associated with a lower chance of experiencing ischemic stroke. Other studies found that the consumption of omega-3s reduced the chance of vascular disease, heart attack, inflammation, heart arrhythmias, sudden cardiac death, atherosclerosis and ischemic, but not hemorrhagic, stroke.
In the secondary prevention of cardiovascular disease—that is, prevention following the occurrence of an initial coronary incident—studies have largely concluded that the consumption of fish or omega-3s significantly reduces the chance of another heart attack or major cardiac event. The American Heart Association and many other professional groups have recommended the consumption of at least two fish meals a week to reduce the chance of heart disease. They note, too, that the plant-based omega-3 alpha-linolenic acid has only weak effects on heart disease and does not affect as many factors as the omega-3s in seafood.
Omega-3s and vascular disease
The precise mechanisms for how omega-3s affect vascular disease are becoming better understood. Long-chain omega-3s are key components of cell membranes where they affect the communication within and between cells. By partially replacing their corresponding omega-6 counterparts in membranes, omega-3s can dampen the effect of omega-6s on inflammation and heart arrhythmias. In vascular endothelial cells, omega-3s have numerous anti-inflammatory effects, especially at the sites where plaque accumulates.
Omega-3 fatty acids affect all stages of vascular disease, including alterations in blood lipids and lipoproteins, blood pressure, platelet adhesiveness, relaxation of the arteries (which eases blood flow and lowers blood pressure), changes in the electrical properties of the heart and alterations in gene expression. Omega-3 fatty acids also reduce the growth of endothelial cells and the release of growth factors from injured blood vessels. These effects may help reduce the recurrence of narrowed blood vessels.
MAINTAINING VASCULAR HEALTH THROUGH DIET
Establish healthy eating habits
Making healthy eating habits a way of life contributes beneficial nutrients and diminishes many conditions that promote vascular disease and other disorders. Healthy food patterns, especially when accompanied by positive lifestyle habits such as exercising regularly and not smoking, can improve endothelial function, too. Improved nutrition has also been associated with less peripheral artery disease. Eating patterns like those in the Mediterranean (Figure 3) and the DASH diets minimize the intake of saturated and trans fatty acids, too much salt, and fried and heavily processed foods. Instead, they emphasize eating generous amounts of fruits and vegetables, cereals rich in dietary fiber, fats such as olive and canola oils, herbs and spices instead of salt, nuts, moderate red wine, very little red meat, and eating fish and shellfish at least twice a week.
Increase omega-3 intake
In North America and elsewhere, current dietary intakes of omega-3s are well below those recommended by the American Heart Association and other health authorities. In the U.S., an average of 100 to 150 mg of omega-3s is consumed daily. Intakes of 250 to 500 mg per day are considered more beneficial to health. People with higher intakes of omega-3s have healthier endothelial function compared with those whose intakes are low. Thus, increasing omega-3 intake is likely to benefit vascular function, inflammatory processes and the diseases associated with these conditions.
A food-based approach to increasing omega-3 consumption means regularly including items such as seafood—especially fatty fish—and many products enriched with long-chain omega-3s. These include eggs, yogurt, milk, spreads, some juices and beverages, and certain snack foods. The caution is that foods claiming to have omega-3s may contain only the plant-based omega-3 alpha-linolenic acid. This omega-3 usually has only weak effects or none on many vascular and heart disease risk factors. The only way to know which omega-3s are in a product is to read the food ingredient label.
For people who do not eat fish, vegetarians or those needing about one gram a day of omega-3s to control their blood cholesterol or triglycerides, fish oil supplements may be a safer and easier way to reach the higher doses of omega-3s recommended. The US Food and Drug Administration considers intakes up to 3 grams a day to be safe.
There is now substantial evidence that regular consumption of omega-3s in amounts of 250 to 500 mg per day benefits vascular health and function and reduces the dangers of heart disease and several other chronic health conditions. Consuming more of these fatty acids may be one of the easiest and most effective ways of protecting the cardiovascular system.
*A fully referenced version of this article is available from the editor.