For many years, the exact reasons for sleep have been a difficult puzzle for scientists to put together. Some say it rejuvenates the exhausted brain, yet we know that the brain remains quite active during sleep, when memories are consolidated. Some studies have suggested that our most creative thoughts occur when we are asleep. Studies on brain activity and metabolism also suggest that rest is not the primary object of sleep.

The discovery of the brain’s glymphatic system may provide the answer to the question of why we sleep. Scientists have found that during sleep, the brain actually shrinks slightly, opening glymphatic channels that allow greater clearance of toxic molecules from the brain’s tissues. In fact, the glymphatic system works best when we are asleep.

On the other hand, when people are awake and mentally busy, glymphatic flow slows and toxic molecules build up in the brain. Sleep is required to clear the waste that accumulates during the daytime. Careful studies using animals have demonstrated that the brain’s glymphatic system worked best when sleeping on the side, rather than on the back.

Dr. Jerry Lemole has studied the glymphatic system carefully, and is working on the details of how its impairment is linked to Alzheimer’s disease and (possibly) other neurodegenerative disorders. He is also writing a book on how to improve lymphatic flow.

How much sleep a person needs varies, especially with aging. Older people may need as little as five to six hours of restful sleep a night, while younger children require at least eight hours.

Sleep is critical for childhood growth, as each time children fall asleep their pituitary gland secretes a burst of growth hormone. This is true even for short naps. If repeated or prolonged, sleep deprivation can result in damage to the brain, especially the hippocampus.

The compound gotu kola (Centella asiatica) has been shown to reduce anxiety and stress, and reduce injury to the brain caused by sleep deprivation. It can also be used to treat insomnia.

Ashwagandha (Withania somnifera) also reduces stress and anxiety — and importantly, lowers elevated levels of cortisol, which is known to damage the hippocampus and to cause insomnia and waking in the middle of the night.