Diabetes: the overlooked risk factor in stroke

Nutrition Health Review, Summer, 1996

Although all stroke risk factors need to be taken seriously, diabetes may be the one overlooked most often. Many of the 14 million people in the United States with diabetes are unaware that insulin resistance affects more than just the body's ability to use glucose; it also has the potential to dramatically increase blood pressure.

Hypertension is a major complication leading to stroke in diabetic patients, who are two to four times more likely than the nondiabetic population to suffer an ischemic stroke. (Diabetes does not appear to increase risk of hemorrhagic stroke.) Because hypertension produces no symptoms except in severe cases, many patients with diabetes realize that they have high blood pressure only after experiencing complications, such as a stroke.

Diabetes is a complex syndrome involving abnormalities of carbohydrate, lipid, and protein metabolism stemming from either a deficiency of insulin or the metabolic effects of insulin on cells. Insulin is a hormone. produced by the pancreas, which regulates the metabolism of glucose and other carbohydrates, lipids, protein, and potassium.

Insulin resistance, such as in type II diabetes, accounts for 90 to 95 percent of all cases of diabetes and affects blood pressure in several ways. Although questions still surround the relationship between hypertension and diabetes, the following may shed light on why diabetic patients as well as obese patients, who also often deal with insulin resistance, have a higher rate of hypertension. In general, high insulin levels associated with insulin resistance in obese patients contribute to high blood pressure.

Insulin induces blood vessel (vascular) growth. A decreased effect of insulin on vascular tissues can lead to increased contraction of blood vessels, thus increasing blood pressure. An analogy is that of a garden hose with a nozzle. When the nozzle is completely open, water flows freely without much force. Partially tighten the nozzle, and pressure in the hose increases. Such is the effect of contracted blood vessels on the flow of blood and vascular pressure.

Insulin also regulates two vascular smooth muscle pumps. Decreased activity of both pumps in accordance with increased levels of intracellular calcium have been reported in insulin-resistant obese states of hypertension. As a result, decreased amounts of insulin in the cells may lead directly to abnormal cellular metabolism and increased external vascular resistance, which can lead to hypertension.

Furthermore, insulin promotes sodium reabsorption from tubules of the kidneys. Obese individuals tend to be sensitive to the salt-retaining action of insulin, which may also influence blood pressure.

Controlling hypertension is vital and requires regular monitoring. The Joint National Committee on the Detection, Evaluation, and Treatment of High Blood Pressure recommends a blood pressure check at least every two years and more often for people with a family history of hypertension. An average systolic blood pressure of 140 millimeters of mercury (mm. Hg.) and above or an average diastolic blood pressure of 90 mm. Hg. and above indicates a diagnosis of high blood pressure. Normal blood pressure is 130/85 mm. Hg. or less.

Although no health organizations recommend routine screening for diabetes, people with a family history of the syndrome should consult their physicians about having their blood glucose levels tested. For diabetics, keeping blood glucose levels under control is equally important. Studies have shown that when blood glucose levels are high at the time of a stroke, brain damage is more severe and extensive than when blood glucose is well-controlled. In addition, special consideration needs to be given in the treatment of diabetes-related hypertension because certain antihypertensive medications can affect diabetes control and worsen complications of the syndrome.

The best defense diabetic patients can have is awareness of hypertension's dire potential in relation to their existing condition. Because people with diabetes also are more susceptible to other stroke risk factors, such as abnormal cholesterol levels, atherosclerosis, and obesity, maintaining a healthful way of life remains essential as well.