May is National High Blood Education Pressure Month and, with about 50 million Americans having high blood pressure, this chronic disorder continues to be a major public health problem.
The May 22, 1996, issue of the Journal of the American Medical Association spotlights the problem of high blood pressure management, as well as new clues into its development and related conditions. Many of these studies were supported by the NHLBI. Three are summarized below--on congestive heart failure, dietary protein, and long-term treatment. NHLBI scientists are available for comment on them.
As NHLBI Director Dr. Claude Lenfant notes in an opening editorial, "Hypertension can be treated successfully," yet current approaches are "less than optimal." Only by learning more about its causes and influences can its occurrence be prevented--the best approach of all.
1 - Hypertension and Congestive Heart Failure
Earlier and more aggressive treatment of hypertension is vital to prevent congestive heart failure (CHF), according to a new study from the Framingham Heart Study. The study team, led by Dr. Daniel Levy, Framingham Heart Study director, found that high blood pressure accounts for nearly 40 percent of CHF in men and nearly 60 percent in women.
The article, "The Progression From Hypertension to Congestive Heart Failure," draws data from both the original Framingham Heart Study and the Framingham Offspring Study. The 5,143 participants, ages 40-89, were followed for at least 20 years, beginning in January 1970. At that time, all were free of CHF.
The study shows that hypertension is the foremost risk factor for CHF--in 91 percent of the cases, it occurred before the development of CHF. And men were two times more likely and women three times more likely to develop heart failure if they had hypertension.
2 - Dietary Protein and Blood Pressure
Animal and vegetable proteins in the diet may lower blood pressure--the opposite of long-held scientific belief. But more research is needed before protein can be added to the list of nutrients that affect blood pressure.
That's the conclusion in "Dietary Protein and Blood Pressure," a major review of data from human and animal observational and intervention studies published or presented since 1980. The authors are Drs. Eva Obarzanek, Paul A. Velletri, and Jeffrey A. Cutler, all of NHLBI.
In the U.S., dietary protein had long been thought to raise blood pressure but newer studies from China, the United States, and elsewhere suggest that animal and vegetable proteins lower blood pressure.
However, animal research has not yet been done to test the link between dietary protein and blood pressure or to uncover the mechanism. In particular, the authors call for the development of animal models.
More human intervention studies are needed too, they add. The few human intervention studies done so far have found no clear sign that protein lowers blood pressure--in part because they were too limited to distinguish the effects of dietary protein from those of other nutrients.
Finally, research also must assess potential kidney problems that might result from a high protein intake in some groups, such as the elderly, according to the authors.
The authors conclude that the enormity of the blood pressure problem in the United States makes urgent the quest to define all possible lifestyle factors that affect blood pressure.
3 - Long-Term Effects of Hypertension Treatments on Plasma Lipids
Lifestyle changes, such as weight loss, a healthy eating plan, and physical activity, are crucial for reducing blood lipids in those treated for Stage I hypertension.
That finding is from the "Long-Term Effects on Plasma Lipids of Diet and Drugs to Treat Hypertension: Results of the Treatment of Mild Hypertension Study (TOMHS)." TOMHS was started in the 1980's to examine the effects on blood pressure and lipids of lifestyle changes alone and in combination with five classes of antihypertensive medication. The five classes are: a diuretic, a beta blocker, an alpha antagonist, a calcium antagonist, and an angiotensin converting enzyme (ACE) inhibitor.
Prior data had suggested that some antihypertensive drugs, such as diuretics and beta blockers, might adversely affect blood lipids, especially if taken in high doses or without dietary changes to counter the adverse effect. Also in question was whether such an adverse effect persisted or waned over time.
TOMHS followed 902 men and women, ages 45-69, with Stage I hypertension (140-159/90-99 mm Hg). Stage I hypertension affects about 36 million Americans. (Normal blood pressure is <130/<85 mm Hg; the level between those is called "high normal" blood pressure.)
The TOMHS Research Group, led by Dr. Richard H. Grimm, Jr., Director, Shapiro Center for Evidence-Based Medicine, Hennepin County Medical Center, University of Minnesota in Minneapolis, found that the lifestyle changes gave significant reductions in blood pressure and long-term improvements in all major lipid fractions. When an antihypertensive drug was used as well, high blood pressure was lowered even more. All antihypertensive drugs worked equally well in reducing blood pressure.
The drugs had varying effects on the lipid fractions but none caused long-term significant adverse effects. Only the alpha antagonist (doxazosin) produced a significant improvement in total cholesterol and low-density lipoprotein cholesterol. An early adverse increase in blood lipids from the diuretic (chlorthalidone) disappeared over time.
"TOMHS findings lend further support," the authors stress, to the need for physicians to counsel hypertensive patients to lose weight and follow a low-fat eating plan. Physicians also should pay attention to a patient's "blood lipid levels when treating high blood pressure," they add.
Making such individualized treatment decisions, however, has been hard for physicians because of persisting questions about some antihypertensive drugs' effects on morbidity and mortality from heart disease and all causes. Several clinical trials are now under way to help answer these questions. One is the 9-year NHLBI-sponsored Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), which expects to enroll about 40,000 patients age 55 and older. It is being conducted through medical practices across the United States--about 500 physicians are participating.
ALLHAT now has a toll-free telephone line that the public can call to find out how to participate in the trial. The number is: 1-888-99-HEART.
Physicians interested in participating in ALLHAT can call the ALLHAT Clinical Trials Center at 1-800-690-7870.
A Special Note: Dietary Sodium and Blood Pressure
The editorial by NHLBI Director Dr. Lenfant also has a refutation of the issue's article, "Effect of Reduced Dietary Sodium on Blood Pressure: A Meta-Analysis of Randomized Controlled Trials." The NHLBI position is contained in a statement from the National High Blood Pressure Education Program on the need for Americans to protect their cardiovascular health by moderating their sodium and salt consumption. The statement's position was adopted in the subsequently issued 1995 U.S. Dietary Guidelines for Americans.