4. Supports the lymphatic system
The lymphatic system is a network of arteries that carries a clear fluid called lymph. This system is key to transporting fluids throughout the body, and is also important for our immune system. The lymphatic system carries toxins and other waste products so a blockage in any part of this system is associated with poor health.
It has long been thought that sleeping on the left side helps the lymphatic system filter out waste. The lymphatic system drains to the left into the thoracic duct, so once again, this position lets gravity do its thing naturally.