Although there are many commonalities in human sleep, there is also a great deal of variation. The average person needs somewhere between seven and nine hours a night, but we all know outliers. Some people seem to survive on as little as four hours per night without an issue while others need ten hours or more in order to function optimally the next day. According to a new study, needing far more sleep than average can give you a higher chance of developing serious cardiovascular disease. Too much sleep raises stroke risk, as does daytime napping and a few other habits we previously considered normal.

The Dangers of Stroke

Stroke affects around 15 million people across the globe every year. These cardiovascular events occur when there is a problem in the blood vessels that supply the brain, leading to decreased blood flow (and thus the supply of oxygen and nutrients) for a long enough time for brain tissues to be permanently harmed. In an ischemic stroke, blood flow is blocked completely, often by a plaque or by a blood clot. In a hemorrhagic stroke, a blood vessel ruptures, flooding the brain with blood at the site of the break while starving cells and tissues that are downstream.

Although common, strokes can be devastating. More than a third of people who get them — around 6 million — will die from the event. Another 5 million will suffer lifelong disability. People who survive the event often lose the use of the affected area of the brain for the rest of their lives. They may have speech deficits or a loss of control over a part of their body. While there are therapies that can train stroke sufferers to perform some tasks using different areas of the brain, many people are left permanently disabled.

There are many risk factors for stroke. Anything that harms your blood vessels, such as high blood pressure and high cholesterol, increases your risk. Behaviors that increase inflammation, such as smoking, can also contribute. According to a new study, abnormal sleep behaviors such as daytime napping and sleeping too much raises stroke risk as well.

How Too Much Sleep Raises Stroke Risk

The new study, performed in China, looked at the health and sleeping habits of 31,750 people who were aged 62. None of the study participants had a history of stroke or any other chronic health condition. Around 8 percent of participants admitted to taking napping for more than 90 minutes on a regular basis. Almost one quarter reported sleeping for at least nine hours every night.

Researchers then followed the participants for around six years, taking note of all major health events. Just over 1,500 people had strokes over this period. When researchers compiled the data, there was an interesting correlation. People who slept longer than nine hours and those who took long daytime naps had an 85 percent increased risk of having a stroke compared to people who slept a short or average amount of time at night.

The quality of sleep also appears to play a role in stroke risk. People who rated their sleep quality as poor were 29 percent more likely to have a stroke.

Sleep and Cardiovascular Health

The researchers involved in this study acknowledge that there are several limitations to their research. First, the study only looks at a correlation or link. They did not look for (and thus did not find) evidence that sleeping too much is a direct cause of stroke. There is a possibility that people who have undiagnosed health issues that lead to stroke may also need more sleep. Second, the study did not look at snoring and sleep apnea, which can decrease sleep quality and increase the amount of time people need to sleep while causing an increased risk of cardiovascular disease.

However, there were some interesting connections. Researchers note that increased sleep needs have been linked to increased cholesterol levels and greater waist circumference, both of which have been linked to cardiovascular disease and increased sleep needs.

Are You Sleeping Too Much?

If you sleep nine or more hours every night, it is important to find the reason. You may have sleep apnea, a disorder in which people suffer airway obstructions that cause snoring and decreased oxygen intake over the night. You also may have poor physical conditioning from a lack of exercise or other lifestyle issues. This can lead to fatigue and increased sleep needs, but it also is a risk factor for cardiovascular disease. Last, you may be in the early stages of heart disease, which can be treated before it leads to a stroke.

Most causes of increased sleep needs are treatable. Although not getting enough sleep is a health risk, needing an increased amount of sleep is a sign that something is wrong with your health. Listening to your body is the first step to getting treatment before you have a devastating health effect.

Sleep is important for your whole-body health. It also can be an important indicator of your overall health. If simple lifestyle changes are not helping you to feel rested after a normal amount of sleep, talk to your doctor about how you can get the medical treatment and rest that you need.