# Sleep is critical to your body The human body needs a good sleep hygiene to function properly; even the US military, who invested a lot of time and money in the search for ways to keep soldiers awake longer, eventually concluded that no treatment could replace lost sleep. Sleep deprivation comes with many problems: it increases levels of *ghrelin*, a hormone which causes you to retain fat and feel more hungry, and *cortisol*, the stress hormone which is linked to visceral fat and promotes muscle breakdown, and it decreases levels of *leptin*, the satiety hormone, *melatonin*, which has anti-ageing and anti-cancer properties and promotes weight loss by increasing brown adipose tissue, and *HGH*, which stimulates growth, cell reproduction and cell regeneration. Furthermore, during sleep, your brain clears 60% more waste — such as amyloid beta which is linked to Alzheimer's — through your glymphatic system. See also [[Quality sleep guidelines]] and [[The frequency following response can help you go to sleep]] to improve your sleep. --- ## 📚 References - [[@whativelearnedWhySleepCritical2017|WHY Sleep is critical for the Body and Brain | Science of Sleep]]