Restless legs syndrome and cardiovascular disease and kidney disease

Restless legs syndrome (RLS) is a chronic neurological condition that causes discomfort in the legs in the evening before sleep. Studies have linked RLS with certain cardiovascular diseases such as high blood pressure. This article is about a study that examined RLS in veterans. Specifically, the researchers studied the relationship between RLS and stroke, heart disease, kidney disease, and mortality rate. The researchers compared about 3700 veterans with and without RLS. Results showed higher amounts of stroke, coronary heart disease, chronic kidney disease, and mortality in those that had RLS compared to those that did not.

The results are not surprising. And as the article points out, the findings don't show that RLS causes strokes, heart disease, or kidney disease. One issue is whether the RLS in these veterans was primary, or secondary to another disorder, such as obstructive sleep apnea (OSA). OSA can significantly worsen RLS, meaning that it may be the OSA that is increasing the incidence of cardiovascular or kidney disease - not necessarily the RLS. Also, RLS is known to be common in patients with chronic kidney disease, especially those on dialysis. More studies are needed to tease out the relationship between RLS and these other disorders.

Sleep duration and stroke risk

I've blogged here and here about stroke risk and sleep duration. The data suggest a U-shaped curve with regards to stroke risk and amount of sleep. This means that those who are short or long sleepers are at increased risk.

This study also examined stroke risk and sleep duration. The data was from a larger cohort study and included over 16,000 participants. Sleep duration and sleep quality were assessed with a self-reported questionnaire. The researchers divided up the participants into short sleeper (<6 hours per night), average sleeper (6-8 hours per night), or long sleeper (> 8 hours per night). Of note, this is an arbitrary definition, although generally agreed upon in our field.

Results showed a J-shaped curve, meaning that longer sleepers had a 46% higher risk of a stroke after adjusting for the usual cardiovascular risk factors. Of note, this result was only significant for those aged 63 and older. And the association remained even if the participant reported sleeping longer, but had good sleep quality.

Short sleepers had an 18% increased risk of stroke, but this was not statistically significant. Both groups were compared to the stroke risk of average length sleepers.

The authors concluded that long sleep duration may be an early sign of increased stroke risk, particularly among healthy people.

Insomnia and stroke

Sleep duration and cardiovascular disease gets lots of press, even though the studies are inconclusive. Some speculate a "U" shaped curve where too little sleep and too much sleep is associated with higher risk of cardiovascular disease. It's unclear, but insomnia gets linked to sleep deprivation, and thus the news runs with stories that insomnia can increase risk of cardiovascular disease. I have blogged about it multiple times, here, here, and here. There are relatively few studies that have examined the relationship between insomnia and stroke.

This study is a retrospective cohort study based in Taiwan. They looked at patients with a diagnosis of insomnia, and used a comparison group without insomnia. They excluded those patients with a known diagnosis of obstructive sleep apnea and those with previous diagnosis of stroke. Then they tracked the populations for 4 years to analyze the number of strokes that occurred. There were 21,438 subjects with insomnia diagnoses and 64,314 subjects without insomnia. As expected, prevalence of diabetes, high blood pressure, high cholesterol, depression, anxiety, and atrial fibrillation were all higher in the insomnia population. During the 4 year follow up period, 583 of the insomnia patients developed stroke, whereas 962 of the patients without insomnia developed stroke. The incidence rate was significantly higher in the insomnia patient group than in the group without insomnia.

Again, there are some important limitations in this study, some of which are not addressed by the study authors. One big one is that we really don't know if the patients had primary or secondary insomnia. For all we know, the patients with insomnia and stroke may all have had undiagnosed obstructive sleep apnea. Also, the researchers relied on a diagnosis code for insomnia, but that does not mean these patients had a clinical interview by a sleep physician to determine that diagnosis. We don't know who is making the diagnosis of insomnia or how it is being made. There seems to be too many details left out to make any reasonable conclusions. I do agree with the authors that we need to screen and treat insomnia. It's also important to make an accurate diagnosis.

The reason I harp on this topic is that many of my patients with chronic insomnia inadvertently worsen their insomnia by worrying about the supposed health effects of insomnia. The news media and magazine articles make "insomnia" sound so dangerous. But if these individuals have primary insomnia, then they are not necessarily at increased risk just from the insomnia alone.

Obstructive sleep apnea, stroke, and atrial fibrillation

Obstructive sleep apnea (OSA), stroke, and atrial fibrillation are related. OSA can increase risk of stroke. So can atrial fibrillation. OSA can make it harder for cardiologists to control atrial fibrillation. Here is a study that studied these three conditions. They monitored people with OSA to see if they had a stroke. In those that did have a stroke, atrial fibrillation was much more common. This suggests a relationship between atrial fibrillation and OSA in stroke development. And this relationship was true after adjusting for common conditions like age, diabetes, body mass index, etc.

Snoring not associated with increased mortality, cardiovascular disease, or stroke

As I have mentioned before, snoring has been implicated in cartoid artery blockages in animals, but not in humans. Obstructive sleep apnea (OSA), however, has been associated with cardiovascular disease and strokes. Here is a study from the Sleep Journal about snoring in humans. Researchers studied 380 subjects by having them undergo a home sleep study to assess snoring and OSA. The subjects were then followed for 17 years and their mortality information, cardiovascular disease incidence, and stroke incidence were recorded.

The results showed no association between snoring and mortality, cardiovascular disease, or strokes, when controlling for OSA and other factors. The results help us appreciate the importance of sleep studies, as they allow us sleep physicians to distinguish snoring from OSA.

Obstructive sleep apnea, stroke, obesity, and type 2 diabetes

Obstructive sleep apnea (OSA), stroke, elevated weight, and type 2 diabetes often exist together. Sorting out what contributes to what is difficult to do. The authors of the study in the Sleep Journal studied how OSA severity is related to cardiovascular disease (CVD) in obese type 2 diabetics. The subjects were studied with home sleep tests and asked subjectively about CVD.

The results showed that the risk of stroke increased with the OSA severity. However, OSA severity did not correlate with increased risk of other CVD like coronary heart disease or heart attack. The authors concluded that moderate to severe OSA could further increase stroke risk in obese type 2 diabetics. Of course, more studies will be need to see if treating OSA in those patients reduces stroke risk.

Snoring and carotid artery blockages

Snoring has been linked to blockages in carotid arteries in animals, but it's not clear if snoring contributes to blocked arteries in humans. In the August edition of the Sleep journal, researchers perform the study on subjects that had had strokes or mini strokes (TIAs). They had the patient's complete questionnaires about snoring and they graded the degree of carotid artery narrowing by ultrasound.

The results showed no association between snoring and carotid artery narrowing. However this study did not assess for obstructive sleep apnea which could increase the risk of stroke. Therefore, in patients who have had strokes, or mini strokes, it can be helpful to have them assessed for obstructive sleep apnea.

Sleep Deprivation and Stroke Risk

This article discusses research presented at the Sleep Meeting in Boston. Researchers discovered that patients who slept less than six hours, per their own self-report, were more likely to have stroke symptoms than those that slept longer. This increased risk occurred despite being normal weight and researchers controlled for other factors associated such as high blood pressure, high cholesterol, and sleep apnea. The effect was greatest in African Americans, which could explain how this racial group is more prone to having stroke than other races.

Obstructive Sleep Apnea in a New Animal Model Shows Damage to Brain Arteries

Here is an article about how scientists have developed a new model of obstructive sleep apnea (OSA) in animals. They used this new model to study the affects of OSA on brain arteries. After one month of moderate OSA, there was visible damage to the arteries in the animals brains. The researchers concluded that this vessel damage could contribute to the increased risk of stroke seen in patients with untreated OSA.

Snoring and Carotid Artery Disease

There is an intersting article in the June edition of the Sleep Journal about how snoring damages the lining of carotid arteries, which are the large arteries in our necks that supply blood to the brain.

The authors of this study had already shown that heavy snoring is an independent risk factor for carotid atherosclerosis (hardening of the artery). It was postulated that the vibration from snoring damaged the lining of the walls of the carotid arteries, which than could lead to atherosclerosis.

In this study, researchers put a vibratory sound, similar to human snoring, next to the carotids in anesthetized rabbits for six hours. Just this one time exposure to snoring vibrations damaged the lining of the carotid artery. The results of this study are interesting because prior epidemiologic studies with self-reported snoring have been contradictory with regards to harmful effects of snoring. But it has been arugued that the reliance on self-reported snoring is inaccurate, particularly in the absence of a bed partner to hear the snoring. And objective measurements of snoring have not been a routine part of sleep medicine. The results of this study have public health implications, as snoring is estimated to occur in almost half of the population. If snoring does damage adjacent blood vessels, this could increase stroke risk. Therefore, as a field, perhaps it is time we sleep physicians developed ways to quantify snoring and to take snoring more seriously.

Sleep Duration and Stroke Risk

A study was presented at the American Heart Association meeting where almost 70,000 female nurses were asked how long they slept on average over a 20 year span of time. The researchers than recorded which women had a stroke and analyzed if a certain number of hours of sleep increased the risk of stroke relative to the baseline average of seven hours per night.

The researchers found that women who slept 10 or more hours had a 63% increase risk of stroke. Those women that slept less than 7 or 8-9 hours per night had an insignificant increase in stroke risk. Of note, the researchers adjusted the risk for other factors like alcohol intake, fruit and vegetable consumption, physical activity, and smoking status. Body mass index and the presence of diabetes and high blood pressure were recorded as potential influential factors.

The researchers were unable to determine any underlying biological mechanism that could cause the increased risk of stroke in longer sleepers.

I wonder if some of the women have untreated sleep apnea, which can cause longer sleep durations, in an attempt to get more rest. Untreated sleep apnea does increase the risk of stroke.

Longer sleep durations could mean that these women have brains that function differently or are structurally different, and perhaps those differences could account for the increased stroke risk.

Sleep Apnea Treatment, Stroke Recovery, and Cardiovascular Events

In the September 16th edition of the European Respiratory Journal, there was a study done to assess the benefits of early CPAP treatment on funtional outcome, quality of life, and rates of new cardiovascular events and mortality in patients who suffered their first stroke.

In this study, 325 patients were randomized to CPAP treatment or a control group that did not receive CPAP. 90.5% of the CPAP group had improvements in neurological assessments in one month, which was significantly greater than the 56.3% that showed improvement in the control group. Beyond one month though, results between the two groups did not differ significantly.

Cardiovascular mortality rates did not differ significantly between the two groups. However, the average time from the stroke to the first cardiovascular event was significantly longer in the CPAP group (15 months) than in controls (8 months). This implies that CPAP might help delay the onset of new cardiovascular events in a patient population already at high risk for cardiovascular disease.

Sleep Duration and Cardiovascular Disease

The August edition of the journal Sleep has an article about the association of sleep duration and cardiovascular disease. It was based on a survey of over 30,000 Americans. The results showed that cardiovascular disease was more common in people who reported that they slept less than or greater than seven hours per night. These results were independent of age, sex, race, ethnicity, smoking, alcohol use, body mass index, physical activity, diabetes, high blood pressure, and depression.

The authors of the study did not determine the reason why sleep duration could affect cardiovascular disease, but they provided some theories. Hormonal and metabolic changes can occur in people who sleep less than seven hours, and these changes could impact cardiovascular health. People who sleep longer than seven hours could be sleeping that long due to an underlying sleep disorder, such as obstructive sleep apnea (OSA). OSA can impact cardiovascular health in a negative way.

Getting seven hours of sleep each night may not prevent you from having a heart attack, but getting the right amount of sleep can be an important part of overall good health.