This video explains it beautifully :

This is one of the first wild herbal medicines to come into season after the winter and in this capacity its nutritional profile is near perfect. In days gone by, most of us survived winter on a diet heavy in meat, grains and preserved foods; this diet was severely lacking in vitamins, minerals, antioxidants and micro-nutrients. As such, when March arrived, the appearance of these little green shoots were eagerly awaited as a potent source of nutrients. In fact, they are one of the most nutritiously dense plants growing in Europe and acts perfectly as an all-in-one multivitamin and multi-mineral to re-balance the nutrients lost during the winter months. Western science now supports this notion, showing that nettles contain incredibly high levels of vitamin C and iron, along with vitamin A, most B vitamins, potassium, calcium, chromium, copper, magnesium and zinc. Adenosine triphosphate, or ATP, is often referred to as the “molecular unit of currency” in the cellular energy economy because it is the primary molecule used by cells to store and transfer energy. When our cells carry a high level of toxins (often called exogenous toxins) it impairs cell function, and reduces the production and usage of ATP, thereby reducing collective levels of cellular energy output, which is what makes you feel tired and lethargic. This easy to forage herb can help, by simulating liver function, and in particular the clearance of cellular toxin.