A recent study shows a link between sleep and heart attack risk.

The New England Journal of Medicine reported on a study that looked at the effect of daylight-savings time on heart attack risk the week following the time changes. It reported fewer heart attacks after the fall time change compared to an increase in heart attacks following the spring time change.

The reason could be the stress placed on the heart when waking up earlier than the body is used to waking up.This process is not disrupted as much in the fall when an extra hour of sleep is gained through the time change.

"When you get up an hour earlier, the body is not ready," said Dr. John Windsor, chief of cardiology at St. Alexius Medical Center. "Subsequently, heart attacks occur."

Heart attacks occur in response to stress on the cardiovascular system. The time change is harder on men in the fall and women in the spring, said Lana Curl, director of the Medcenter One Sleep Center. The reason is not yet clear, she said. It does appear to increase for people with heart attack risk factors.

The body starts to wake up when the brain increases adrenaline. The adrenaline increases the heart rate and blood pressure.

"Adrenaline acts like an alarm clock," he said.

In turn, this increases oxygen in the blood and thins the blood. The blood is thickest when the body starts to wake up, which also makes it more likely to clot. The change in heart rate and blood pressure can cause stress where the arteries are narrowed by cholesterol deposits.

When a person's body reacts to stress, heart rate and blood pressure also increase.

"Mondays are notorious for heart attacks," Curl said.

Part of the reason is that people change their sleep schedule on the weekend, and the stress of starting the work week is greatest Monday morning.

The upcoming holidays, however, are when hospitals see the most patients with heart attacks. Christmas day and New Year's day have the most, out of any other day of the year, Windsor said. The cause is a change in eating habits, sleeping habits and holiday stress. These changes pose a risk for people already prone to a heart attack.

"Holidays are a stressful time," he said. "The body does not identify good stress from bad stress. A wedding is as stressful on the body as a funeral."

Heart attack symptoms are different in men than women. Women generally experience fatigue, shortness of breath and weakness, and men feel chest heaviness, shortness of breath and excessive sweating, he said.

People won't necessarily have a heart attack when they are experiencing stress, but once they begin to feel less stress.

Windsor recommends people at risk of a heart attack to get regular aerobic exercise and eat foods low in fat and cholesterol. People also should moderate how much they drink to no more than a glass or two of wine on occasion, he said. People should also stop smoking, he said.

The heart also is taxed when people have obstructive sleep apnea, one of the most common sleep disorders, Curl said. This is caused when a person stops breathing, which in turn reduces the oxygen available to the heart. Sleep apnea occurs in 10 percent to 20 percent of the population.

Besides a sleep disorder, other risk factors for heart attack include weight, cholesterol and blood pressure.

"In the last year, there has been an increase of cardiac referrals by 20 percent," she said.

One of the reasons Curl sees heart patients referred for sleep tests is when blood pressure cannot be controlled by medication.

(Reach reporter Sara Kincaid at 250-8251 or sara.kincaid@;bismarcktribune.com.)