Cholesterol and Blood Vessels
By Fred Bove, M.D., Ph.D.
I was recently asked how we can screen divers to prevent heart attacks while diving. Should we do stress tests, electrocardiograms or other procedures to be sure a diver is not at risk?
Long before these tests become necessary, we should be working to minimize risk factors for blood vessel disease. This is strongly related to the fats (lipids) in the blood, made up mainly of cholesterol and triglycerides. Cholesterol is usually made in the body but can be found in egg yolks, poultry skin and some shellfish; triglycerides are obtained from foods in addition to being made in the body. Individuals with abnormally high levels of blood fats are at high risk for developing atherosclerosis (hardening of the arteries). When the arteries that supply blood to the heart or brain are narrowed, these organs are deprived of oxygen. The heart may be damaged or may develop abnormal rhythms that may become lethal. Inadequate blood supply to the brain causes strokes.
Surveys of sudden death in adults, related to physical activity, indicate that most of these incidents are owing to narrowing of the coronary arteries.
Narrowing may occur over many years without any sensation until a severe obstruction is present or the severely narrowed artery is completely blocked by a blood clot and a heart attack occurs. In the case of narrowed arteries to the brain, a disabling stroke may occur. Atherosclerosis can also cause abnormal kidney function and disease of the blood vessels to the legs, which will cause severe disability owing to pain and amputation when the limb is severely damaged by lack of oxygen.
Atherosclerosis is accelerated by cigarette smoking, elevated blood lipids, hypertension, diabetes and lack of exercise; it progresses with age. The diver who is most prone to blood vessel problems is a male more than 40 years old who is a long term smoker, has hypertension, is overweight, has abnormal blood lipids and does not exercise. Unfortunately, this describes a significant portion of the sport diving community and raises concern for heart attack risk while doing any form of exercise, including diving. Since individuals in their 50s, 60s and even 70s are becoming divers, some individuals with undetected blood vessel disease will be diving.
DIET AND LIPIDS
Blood lipids include cholesterol, triglycerides and the components of cholesterol, high density lipoprotein (HDL) and low density lipoprotein (LDL). The ideal situation is a cholesterol level below 200 mg/dl, an LDL below 130 mg/dl, an HDL above 35 mg/dl and triglycerides below 150 mg/dl. High blood cholesterol and high LDL are known to increase risk for blood vessel damage and heart disease, stroke, kidney failure and loss of limbs.
Blood lipid tests are usually ordered along with other blood tests by your physician. A physical exam done periodically, which includes a blood pressure check, a test for blood lipids, blood sugar and measures of kidney function, will give you the information needed to reduce your risk of blood vessel disease.
Blood lipids are strongly influenced by your diet. We hear constantly that there is too much fat in the American diet, which raises the levels of fat (lipids) in the blood. Eventually some of this fat is deposited in blood vessels and causes atherosclerosis. A healthy diet limits fat to 30 percent of the total diet or about 50 grams of fat a day. An example of a daily adult diet would be a total of 1,500 calories, with 450 from fat, 900 from carbohydrates and the rest from protein. If you are exercising frequently and using more than 1,500 calories daily, the additional calories are best made up of carbohydrates. Reducing animal fats will also contribute to reducing blood cholesterol and LDL.
If you have trouble getting your blood cholesterol below 200 (mg/dl) you may need medication. Most people with cholesterol levels above 200 would benefit from a cholesterol lowering medication if diet cannot bring the value to that level. Triglycerides are influenced strongly by body weight and blood sugar. Most adults who are significantly overweight will ultimately develop diabetes, one of the serious risk factors for blood vessel disease. Long standing diabetes often causes damage to blood vessels in the heart, kidneys, brain and legs. Many diabetics suffer severely from poor circulation in the feet and legs, from kidney disease, strokes and heart attacks.
A person who is overweight, with diabetes, hypertension, high blood cholesterol and who smokes is at very high risk for developing blood vessel disease in the heart, brain, kidneys and legs.
For safe diving, you should know your risk for blood vessel disease. Your physician can provide you with the information you need to take care of your blood vessels, and advice on how to minimize your risk of heart attack, stroke and other damage. You can find previous medical columns and other diving medicine information on our Web site: www.scubamed.com.