June 2001

From American Heart Association

The heart has no need for weed, especially for middle-aged people

DALLAS, June 12 – Researchers who previously reported that marijuana is a trigger for heart attack are now warning that the drug may play a more pivotal role as some users enter middle age – a time when their risk for heart disease is already increasing – according to a study in today’s Circulation: Journal of the American Heart Association.

In a study of individuals who have had heart attacks, the risk of heart attack was 4.8 times higher in the first hour after smoking marijuana compared to periods of nonuse, reports Murray A. Mittleman, M.D., Dr.PH., lead author of the study and director of cardiovascular epidemiology at Beth Israel Deaconess Medical Center in Boston. The risk was 1.7 in the second hour after smoking the drug, and was about the same as the risk of a non-user after that.

“Marijuana use in the age group prone to coronary artery disease is higher than it was in the past,” says Mittleman. “As with any risk factor for heart attack, or for heart disease in general, the risks become more pertinent as we grow older. Marijuana use is no exception.”

Studies conducted more than 30 years ago showed that marijuana use could provoke angina, or chest pain. Smoking marijuana has been shown to increase heart rate and alter blood pressure. It may also trigger a heart attack by causing a plaque inside a coronary artery to rupture and form a clot, which can block the flow of blood to the heart muscle. In addition, the researchers say marijuana is associated with an increase in the heart’s demand for oxygen, while at the same time decreasing the supply of oxygen. Thus, some marijuana-associated heart attacks may be caused by an oxygen supply to the heart that is inadequate to cope with the increased oxygen demands that occur as a result of smoking the drug.

Among the study participants, 124 people (116 men and 8 women) reported smoking marijuana within the year prior to their heart attack. Marijuana users were about 44 years old on average with 23 percent aged 50 to 69.

Mittleman and his associates reviewed data on 3,882 people enrolled in the Determinants of Myocardial Infarction Onset Study, a study aimed at gathering more information about factors associated with myocardial infarction, or heart attack. The study population comprised 2,624 men and 1,258 women aged 20 to 92 years, all of whom had been interviewed an average of four days after having a heart attack. Among 37 individuals who said they smoked marijuana within 24 hours of their heart attacks, 28 (76 percent) reported smoking it at least weekly. In addition, seven of nine patients (78 percent) who reported smoking marijuana within one hour of the onset of heart attack symptoms said they were weekly users. The majority of marijuana smokers, 67.7 percent, reported at least monthly use, while 41.2 percent of users said they smoked marijuana at least weekly.

Relative risk was estimated by comparing the frequency of marijuana use in each of the two hours before heart attack symptoms began with the expected frequency of marijuana use over the prior year (according to the patients’ reports of how often they used it). “Although the relative risk does not appear to vary with age, the absolute increase in risk associated with smoking marijuana is greater for people whose risk is higher to begin with,” says Mittleman. For example, he explains that the absolute risk that a 20-year-old will have a heart attack in the next hour is almost zero. The same risk for a 50-year-old is higher. If both of these individuals smoke marijuana in the next hour, and the risk for each individual increases five-fold, then the absolute increase in risk will be much greater for the 50-year-old, he says.

Compared to non-users, marijuana smokers were more likely to be men (94 percent vs. 67 percent), to be current cigarette smokers (68 percent vs. 32 percent), and to be obese (43 percent vs. 32 percent). Users were less likely to have a history of angina (12 percent vs. 25 percent of nonusers) or high blood pressure (30 percent vs. 44 percent).

The study is the latest in a series of analyses looking at activities of the 3,882 people at or near the time of a heart attack. The objective is to identify possible triggers of heart attack and acquire more information about how people at risk might avoid heart attacks. Previous evaluations of the study population identified strenuous physical activity and sexual intercourse as infrequent triggers of myocardial infarction.

“The risk associated with marijuana use is about the same as the risk we found for strenuous physical exertion,” says Mittleman. “The risk with marijuana use was a little higher than what was observed for sexual intercourse.”

The risk of heart attack associated with marijuana use is much smaller than the association with cocaine use, which confers about a 25-fold increased risk of heart attack during the first hour, he adds. The investigators identified a few people who engaged in physical activity or sexual intercourse, as well as marijuana use, prior to their heart attacks, but the numbers were too small to allow them to determine whether the risk was further increased in those people.

“Understanding the mechanism by which marijuana use causes a heart attack may provide insight into the triggering of infarction by this and other stressors,” says Mittleman.

Co-authors of the study include Rebecca A. Lewis; Malcolm Maclure, Sc.D.; Jane B. Sherwood, R.N.; and James E. Muller, M.D. This study was supported by a grant from the National Heart, Lung and Blood Institute.

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please call: (214) 706-1396
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NR01-1301 (Circ/marijuana)
Media Advisory: Dr. Mittleman can be reached at (617) 632-7653. His e-mail is mmittlem@caregroup.harvard.edu. His fax is (617) 632-7675. (Please do not publish contact information.)

This article comes from Science Blog. Copyright © 2004

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