The role of sleep and growth hormone in promoting human growth has long been established. It has also been found that sleep helps stimulate HGH levels. Human growth hormone (HGH) stimulates biological activity that converts glucose into glycogen, which is used as energy during physical activities and rest. During the night, high levels of HGH can help support healthy growth and repair of the human body's tissues. Without adequate sleep, the level of HGH begins to decline causing low energy levels, aching joints and other signs of ageing.