Friday, March 30, 2012

Sleeping Less Than 6 Hours... or more than 8? Enter Heart Disease.

I'm always scanning the literature in different specialties for relevant articles befitting issues in sleep and neurology. This is a great and appropriate look at what happens when we sleep too little or two long. There is actually numerous studies showing that a window of greater than 6 but less than 8 hours is the healthiest range for humans; this is just a current one involving many people and looking at heart health.

This comes from:
Aggarwal S, et al “Sleep patterns and prevalence of cardiovascular outcomes—analysis of National Health and Nutrition Examination Survey Database 2007-08” American College of Cardiology 2012; Abstract 1185-325.
This data involved more than 3,000 people older than 45 who participated in the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2008.
In a nationally representative study, getting less than 6 hours of sleep each night was associated an increased likelihood of having:
Congestive heart failure (1.67 times more likely)
Heart attack (2.01 times more likely)
Stroke (2.01 times more likely)

BUT, sleeping more than 8 hours was associated with greater odds of having:
Coronary artery disease (1.19 times more likely)
Chest pain (2.07 times more likely)

The findings are consistent with prior studies that have identified relationships between the quality and duration of sleep and heart health.
Another recent study of more than 140,000 participants showed that perceived sleep disturbance on at least 3 nights out of the week was associated with obesity, diabetes, MI, coronary artery disease, and stroke.

A 2008 study showed a relationship between shorter sleep duration and an indicator of coronary artery disease. In that study, each additional hour of sleep was associated with a 33% lower likelihood of coronary artery calcification.

And a large Norwegian study found that people who had trouble falling or staying asleep appeared to have an elevated risk of MI.

Although an observational study cannot prove cause and effect, there are possible mechanisms through which getting too little sleep may worsen cardiovascular health.
Shorter sleep duration has been tied to hyperactivation of the sympathetic nervous system, glucose intolerance, increased cortisol levels, increased blood pressure, decreased variability in heart rate, disruption of the hypothalamic axis, and increased inflammation.
A possible mechanism for the relationship between too much sleep and cardiovascular outcomes is less clear, but it could be that patients who are sleeping for more than 8 hours a night have more underlying coronary artery disease and angina to begin with, more comorbid conditions like chronic obstructive pulmonary disease or diabetes, or socioeconomic circumstances that cause them to sleep longer.
The researchers acknowledged some limitations of the analysis, including the retrospective design, the possible influence of recall bias, and the lack of information on sleep quality.