Good quality sleep is linked to overall physical and mental health, but is sleeping too much bad for you? Put simply, it can be. Oversleeping, as well as a lack of it, has been linked to a higher risk of chronic illnesses including coronary heart disease, type 2 diabetes, anxiety and obesity in adults aged 45-plus, according to a study published in PLoS one.

But why is sleep important? Theresa Schnorbach, a psychologist and sleep scientist specializing in Clinical Psychology and Cognitive Neuropsychology, tells Live Science that it’s critical to maintaining our physical and mental wellbeing.

“It is essential for regulating the body’s metabolic and hormonal processes,” she says. “It also serves a restorative purpose by flushing out the toxins accumulated in the brain. Sleep also strengthens our immune system by enabling specialized immune cells to work more efficiently at fighting off infections.

Not to mention, it can also help us to heal emotional wounds. “During the rapid eye movement (REM) sleep state, which usually occurs around 90 minutes into the sleep cycle, concentrations of the stress-related, anxiety-triggering chemical noradrenaline are shut off within the brain,” Schnorbach says. “Simultaneously, the brain’s emotion and memory-related structures are reactivated, helping us to process upsetting memories or experiences.”

You can monitor your sleep using one of the best fitness trackers or sleep apps, but ironically, if you spend too much time asleep you will probably still wake up feeling tired and lethargic. This is because any significant deviation from regular sleep patterns can upset the body’s internal rhythm and increase daytime fatigue. Here, we’ll find out more about what happens when you oversleep, and just how much sleep you should be getting.

How much sleep should you get a night?

Dr. Guy Meadows, clinical lead and co-founder at Sleep School, says that sleep is our natural way to recharge, repair and even detoxify our body and mind from the previous day’s efforts and stresses, preparing us to perform at our best again and again.

But how much sleep you need depends on your age, activity level, general health and lifestyle, and this figure will change over the course of your life.

Generally, the Centers for Disease Control and Prevention (CDC) recommends seven to nine hours for adults, eifght to ten hours for teenagers and 14-17 hours for new-borns. During times of stress or illness you may feel you need more sleep than usual.

Theresa Schnorbach

Theresa Schnorbach is a psychologist and sleep scientist, specializing in clinical psychology and cognitive neuropsychology. She has completed a post-graduate training in cognitive behavioural therapy for insomnia (CBT-I) with the German Sleep Society, endorsed by the European Research Society.

Related: What are the best supplements for sleep?

When is oversleeping a problem?

The ‘right’ amount of sleep can be a little subjective – with some people feeling fantastic after having seven hours, while others might need a bit more.

According to the Sleep Foundation, oversleeping (also known as long sleeping) is defined as sleeping more than nine hours — a length of time that most experts agree is excessive for adults.

Sleep disorders

“Oversleeping is often associated with physical or mental disorders, such as sleep apnea, depression, or side effects of medications, and effects that may be linked to over-sleeping including diabetes, heart disease, obesity, and mental illness,” Schnorbach tells Live Science.

Hypersomnia – the opposite of insomnia – is a condition where you both oversleep and feel excessively sleepy during the day. Narcolepsy and other sleep disorders commonly cause hypersomnia.

Meadows says: “Hypersomnia is characterized by excessive daytime sleepiness whereby you might feel the urge to sleep for longer than you need and yet still wake tired. Hypersomnia can be both primary and secondary. Primary means that there is usually no identifiable cause; secondary suggests that other medical conditions, mental health issues, drugs, sleep disorders or a lack of sleep due to shift work could be the cause.”

Impaired brain function

Sleeping too much – more than eight hours – could have a detrimental effect on the brain, according to the world’s biggest sleep study published in the journal Sleep. Neuroscientists at Western University’s Brain and Mind Institute found that too much shut-eye could reduce cognitive ability and reasoning skills.

Weight gain

Research published in Sleep found that people who slept for nine to 10 hours a night were 21% more likely to become obese over a six-year period compared with those who slept for seven to eight hours. The link between sleep time and obesity was the same even when food intake and exercise were factored.

Related: How does sleep affect weight loss?

Depression and mental health

Oversleeping is a possible symptom of depression and anxiety and can make things worse. A study published in Sleep Medicine Reviews found that long sleepers had a higher rate of depression.

Lifestyle factors

If you don’t get enough sleep because of lifestyle factors, such as drinking too much alcohol or taking certain prescription medicines, your body tries to make up for it by oversleeping. Studies have found that having too much sleep can play a role in increased inflammation in the body, which is connected to an increased risk of a ton of health conditions from diabetes to Alzheimer’s.

“Poor lifestyle habits that negatively affect sleep quality and duration include excessive consumption of caffeine, alcohol, sugar and nicotine, as well as lack of exercise,” says Meadows. “Live a healthy lifestyle that promotes sleep. Aim to drink no more than two to three caffeinated beverages per day and switch to herbal or decaf alternatives at midday. Be active everyday, opting for aerobic type exercise such as walking, dancing or jogging versus weight training or sprinting. Aim to leave at least two hours between your workout and bedtime to allow your core body temperature to cool.

If you are sleeping too much, Schnorbach suggests looking at your lifestyle to see if there are any habits that could be impacting the quality of your sleep, and leading you to oversleep.

“I would also recommend speaking to a doctor or healthcare professional as oversleeping could be a symptom of a physical or mental health issue,” she says.

This article is for informational purposes only and is not meant to offer medical advice.