What Happens to Your Body If You Sleep Less Than 6 Hours a Night, Doctors Say

You may have heart trouble.

Getting less than the recommended amount of sleep can result in symptoms that range from mild to severe—and cardiovascular symptoms are some of the most dangerous among them, experts say.

"Insufficient sleep results in increased activity of the sympathetic nervous system, leading to increased heart rate, vasoconstriction, and elevated blood pressure levels," explains Taryn Fernandes, MD, a supervising physician at MEDvidi, an online mental health treatment center. "Lack of adequate sleep has been linked to a higher risk of developing hypertension, as well as cardiovascular diseases like stroke, coronary heart disease, and myocardial infarction," she adds.

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You may experience hormonal disturbances.

Additionally, getting the recommended seven to nine hours of sleep per night is vital for regulating the body's hormonal balance. "Sleep deprivation can interfere with the normal production of hormones like cortisol, insulin, and growth hormone," Fernandes says.

Rigved Tadwalkar, MD, a board-certified cardiologist at Providence Saint John's Health Center in Santa Monica, CA, says sleep can interfere with your hormones in other ways, as well. "Indirectly, poor sleep contributes to the disregulation of hormones implicated in hunger," he tells Best Life. "This contributes to obesity, which is a strong risk factor for cardiovascular disease."

You may suffer increased mental health issues.

Sleep deprivation can also have an outsized impact on your mental health, says Fernandes. Specifically, getting inadequate sleep has been linked with higher incidence of anxiety, depression, and other mood disorders.

"Lack of sleep may increase susceptibility to psychiatric disorders, such as bipolar disorder and schizophrenia, since sleep plays a crucial role in memory consolidation, emotional regulation, and cognitive functioning," explains Fernandes. She notes that regularly getting less than six hours of sleep per night can cause mood swings, irritability, and decreased motivation.

Your immune system may become weakened.

Since sleep is important in maintaining a healthy immune system, sleeping less than six hours per night could also translate into more frequent sickness. "During sleep, the body produces cytokines, a type of protein that aids in fighting infection, inflammation, and stress," explains Fernandes. "Lack of sleep can lower the production of cytokines, which can weaken the immune system and increase vulnerability to illnesses."

In fact, studies show that when you slash your sleep hours for even a few nights at a time, you produce a reduced immune response—even if you make up for your lost sleep later. "Restricting sleep to four hours per night for six days, followed by sleep for 12 hours per night for seven days, resulted in a greater than 50 percent decrease in production of antibodies to influenza vaccination, in comparison with subjects who had regular sleep hours," writes the Centers for Disease Control and Prevention (CDC).

You may be more vulnerable to dementia.

Sleep is essential for optimal brain function, including memory consolidation, learning, and creativity. "Normally, a good night's sleep literally allows for repair and restoration of brain function to the levels seen at the beginning of the prior day," explains David Merrill, MD, PhD, a geriatric psychiatrist and director of the Pacific Neuroscience Institute's Pacific Brain Health Center in Santa Monica, CA.

Merrill tells Best Life that the brain's "specialized cleaning system," known as the glymphatic system, is most active during the deepest stages of sleep. When the glymphatic system becomes dysfunctional, neurotoxic waste products can accumulate in the brain, leaving you more vulnerable to dementia.

"Sleep disturbances increase dementia risk, but unfortunately, dementia itself can also lead to sleep disturbances," Merrill says. "So you can end up with sleep worsening memory to the point of dementia, which then worsens sleep. In this way, disrupted sleep can be part of a downward spiral, making it all the more important to identify and treat sleep issues during early and mid-life adult development. Ideally, sleep will be optimized years before the potential onset of dementia. The hope is that with improved sleep, we can actually delay the age of onset of dementia. The goal of improving sleep is to extend a person's health span for as long into their life as possible," he adds.

You may feel fatigued.

It should come as no surprise that you may feel tired or fatigued after getting too little sleep—but you may be surprised by just how pronounced your lethargy may be. The Cleveland Clinic points out that fatigue from poor sleep can cause very disruptive symptoms that interfere with even the most routine activities.

For some people, this can lead to an increased incidence of injury or accidents—including car accidents. According to a 2018 study published in the journal BMC Medicine, "sleeping six hours per night was associated with a 33 percent increased crash risk, compared to sleeping seven or eight hours per night."

Your eye health may suffer.

According to Besty S. Jacob, a Florida-based optometrist at True Eye Experts, inadequate sleep can also negatively impact your ocular health.

"Sleeping less than six hours can lead to dry eyes, dark circles, and blurry vision. This is because when we don't get the proper amount of rest, our body does not produce tears as efficiently," says Jacob. "This leads to increased friction in the eye which causes redness and irritation and can eventually lead to more serious conditions such as conjunctivitis or blepharitis," he adds.

You may be at higher risk of metabolic diseases.

Sleep deprivation has been linked with increased risk of developing a metabolic disease such as Type 2 diabetes. It also contributes to poorer outcomes for individuals who have already been diagnosed with a metabolic disease.

"If you get less than seven hours of sleep per night regularly, your diabetes will be harder to manage," explains the CDC. They note that too little sleep can increase insulin resistance, make you feel hungrier, make it harder to maintain a healthy diet and weight, and can raise your blood pressure. Since hypertension is already twice as likely in those with diabetes, this can pose a danger to those already at high risk of the condition.

You may notice lower physical performance levels.

Finally, you may notice that getting less than six hours of sleep per night hinders your physical endurance.  "Not only does quality sleep play a role in overall health and wellness, but it is also crucial to optimal performance—in athletics and life in general," explains Vernon Williams, MD, a sports neurologist, pain management specialist, and founding director of the Center for Sports Neurology and Pain Medicine at Cedars-Sinai Kerlan-Jobe Institute in Los Angeles.

"Studies have shown that getting less than six hours of sleep at night is associated with decreased time to physical exhaustion, reduced aerobic output, reduced peak and sustained muscle strength, impaired metabolic capabilities, and increased injury risk," he adds.

In fact, Williams says that sleep health and optimization of sleep efficiency may be the most effective intervention a person can make to "optimize their overall performance, whether on a sports court, in a classroom, or at work."