Getting enough sleep on a regular basis is one important way to protect the health of your heart. Poor and insufficient sleep is associated with a range of cardiovascular problems, including high blood pressure, heart attack, and heart failure. Both men and women are at increased risk for these conditions. But we continue to learn that when it comes to health problems associated with sleep, the particular risks to men and women are not always the same. A new study suggests that for women who already have heart disease, poor sleep may be particularly dangerous to their heart health.
Statistics from the American Heart Association reveal that heart disease is a bigger problem for women than most of us think:
- Heart disease is the No. 1 killer of women, and is more deadly than all forms of cancer combined.
- Heart disease causes one in three women's deaths each year, killing approximately one woman every minute.
- An estimated 43 million women in the U.S. are affected by heart disease.
- Since 1984, more women than men have died each year from heart disease.
- Only one in five American women believe that heart disease is her greatest health threat.
Research indicates that poor-quality sleep -- and waking too early in particular--is associated with increased inflammation among women with heart disease. There was no similar association found for men, suggesting that women with heart disease and sleep problems may be at particular risk for inflammation that can be damaging to the heart.
Researchers at the University of California San Francisco investigated the relationship between sleep quality and inflammation linked to coronary heart disease. They also sought information about how an association between sleep and inflammation might differ between men and women. Their investigation included 980 men and women at the outset, and 626 completed the five-year study. All of those included were suffering from coronary heart disease. The average age of men in the study was 66. Women were slightly younger, with an average age of 64. Researchers measured sleep quality by asking participants to rate their sleep over the previous month. They also asked for reports of some of the most common sleep problems, including difficulty falling asleep, difficulty staying asleep, waking frequently throughout the night, and waking too early in the morning. Researchers assessed inflammation levels using three biomarkers: Interkeukin-6, C-reactive protein, and Fibrinogen.
After five years, researchers repeated tests for inflammation and once again sought reports on sleep quality and sleep problems. When they analyzed data for both men and women together, researchers found no links between inflammation and sleep quality. However, when they analyzed data taking gender into account, researchers found a relationship between inflammation and sleep existed for women, but not for men:
- Women who reported poor sleep quality experienced greater increases in levels of inflammation over the five-year period than men.
- Women who reported their sleep quality as "very poor" or "fairly poor." experienced increases to their inflammation markers that were 2.5 times greater than men who reported the same levels of poor sleep.
- The association between inflammation and sleep remained intact for women even after taking into account other factors that might influence inflammation, including age, cardiac function, body mass index, medication use, and lifestyle factors.
- The link between inflammation and sleep for women with coronary heart disease was particularly strong among those women who had a tendency to wake too early in the morning.
- Women were more likely than men to report waking too early. They were slightly more likely than men to report waking frequently during the night and having difficulty falling asleep.
- Because the majority of women in the study were post-menopausal, researchers hypothesized that low estrogen levels might explain the link between poor sleep and inflammation. This question was not examined in the study itself.
This is not the first study to suggest that lack of sleep may be particularly dangerous for women's heart health. Researchers in the United Kingdom also found inflammation linked to lack of sleep in women. This large-scale study included 4,600 adult men and women. As in the current research, changes to women's inflammation levels were linked to sleep problems, whereas no such association was found in men. In an Italian study that included both men and women, women with resistant hypertension -- a form of high blood pressure that is not responsive to medication -- were five times as likely to have sleep problems. There was no similar link between resistant hypertension and poor sleep in men.
This latest study provides some important information about one way that sleep may affect heart health. It's also another reminder that when it comes to health in general and sleep in particular, gender matters. In recent years there has been an increased focus on learning more about the differences in sleep between men and women, and how these differences may contribute to specific health risks. Evidence suggests that circadian rhythms in men and women are markedly different. Our circadian clocks are remarkably sensitive and precise, and even a small difference in circadian timing can have a significant impact on sleep. We need to continue to pay attention to gender differences in sleep, as a way to better understand, diagnose, and treat both sleep problems and the broad array of health concerns now associated with poor sleep.
Michael J. Breus, PhD
The Sleep Doctor®
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