Insufficient sleep ups the risk of heart disease and diabetes. But how much do you really need? Experts reveal a hidden factor beyond 8 hours

Falling asleep easily and waking up refreshed is more than a moment of calm — it is vital for nearly every system in your body. Sleep allows the brain to consolidate memories, clear metabolic waste, regulate hormones, and repair muscles. It also recharges the immune system. According to a report from USA Today, without sufficient rest, vital bodily functions eventually fail, underscoring why sleep is far from a luxury.

The hidden factor: Deep sleep
While most adults are advised to sleep seven to nine hours per night, specialists emphasize that deep sleep, or slow-wave sleep, is where true restoration happens. Dr. Wendy Troxel, senior behavioral sleep scientist at RAND Corporation, notes that deep sleep usually accounts for 10% to 20% of total sleep, roughly 40 to 110 minutes for adults. Dr. Raj Dasgupta, pulmonary and sleep specialist at Huntington Memorial Hospital, explains that during this stage, muscles repair, immunity peaks, and the brain consolidates memories. “Deep sleep is when your body does the heavy lifting of repair and recovery,” he says.

Risks of insufficient sleep
Despite recommendations, CDC data shows over one-third of Americans fail to get even seven hours per night. Sleep deprivation impacts nearly every system, increasing risks of obesity, high blood pressure, diabetes, heart disease, stroke, mental distress, and even mortality. Lack of deep sleep also affects cognition, memory, and mood, and even short-term sleep loss of fewer than five hours can impair reaction times equivalent to alcohol intoxication, Troxel warns.

The benefits of more sleep
Getting the full recommended hours enhances focus, memory, mood, heart and metabolic health, and immunity. Even one additional hour, such as moving from six to seven hours, can sharpen attention, creativity, and decision-making. However, consistently oversleeping beyond nine to ten hours may be linked to obesity and other metabolic issues, though these findings could reflect underlying health problems.

Consistency is key. Maintaining regular bed and wake times stabilizes circadian rhythm and promotes faster, more efficient deep sleep. Creating a cool, dark, quiet sleep environment, limiting late-day caffeine, nicotine, and alcohol, and reducing screen exposure also helps. Pre-sleep routines like reading, meditation, stretching, or a warm bath signal your body it’s time to rest.

Making sleep a priority
“Sleep often feels like the easiest thing to sacrifice when life gets busy,” says Troxel. Experts urge a mindset shift: treat sleep as a foundation for health rather than an afterthought. Focusing on both total sleep and the quality of deep sleep can improve physical, mental, and emotional well-being, proving that it’s not just about hours in bed but truly restorative rest.