Developments in Brief : Blood Platelet Study Finds Clue to Why Risk of Heart Attack Rises in Morning

Blood clot-forming platelets apparently become most active just after people awaken, according to Harvard researchers who said this finding may help explain why the risk of heart attack increases in the morning.

Previously, Dr. James E. Muller and colleagues at Harvard Medical School reported that heart attacks were most likely to occur between 9 a.m. and noon. In an attempt to find out why, they tested the blood of 15 healthy men every three hours for 24 hours, and found that platelets were much more likely to clump together at 9 a.m.--an hour after the subjects arose. There was no significant increase at any other hour.

Heart attacks usually occur when a blood clot blocks a coronary artery narrowed by fat deposits.

The findings, reported in the current issue of the New England Journal of Medicine, do not prove that increased platelet activity causes heart attacks. Rather, they suggest that such activity may be an important component. It could provide researchers with insights into new ways of preventing heart attacks, the nation’s leading killer, Muller said.

There are about 1 million non-fatal heart attacks and about 500,000 deaths from heart attacks each year in the United States.

“We’ve got a disease that accounts for one-fourth of all deaths in the United States each year and we have basically no idea as to why they occur,” he said. “Now we have a clue as to what may precipitate them.”

The researchers speculated that the platelets may become more active in the morning because that is the time when a person becomes more active, triggering the release of substances that influence platelet activity. To test this hypothesis, they studied 10 subjects on alternate mornings after they arose at the normal time and after they delayed arising by lying still in bed. The researchers found that the increase in platelet activity was delayed.

“It’s a clue that some component of the activity of getting up in the morning is causing it,” said Muller, adding that the researchers are now trying to determine which component of arising is involved. “It could be waking up, standing up, beginning the morning activities,” he said.

Dr. Kenneth Shine of UCLA, who is president of the American Heart Assn., said the findings are interesting but need to be confirmed and followed up with additional study.