In an ideal world runners would a healthy, balanced whole food diet would provide us with the perfect balance of nutrients for our daily and exercise requirements. There are times however when this is not happening and supplementation is required. The best supplements for runners are those that provide health benefits not being met by diet alone.
An example of this may be Omega 3 oils which have many benefits such as lowering blood pressure, improving joint mobility and reducing lactic acid threshold.
There has been a lot of talk over recent years about beetroot supplementation improving endurance and cardiorespiratory performance. Beetroot is high in nitrates which metabolise into nitric oxide. Research has shown that nitric oxide can strengthen heart and muscle contractions, increase blood flow and improve lung efficiency. If there is a particular running area that you are struggling in maybe think about overhauling your diet and supplementing if required.