Coenzyme Q10 (CoQ10) is a key part of your cells' energy machinery. It sits inside mitochondria – the “power stations” of your cells – and helps create ATP, the main energy currency your body uses. CoQ10 also acts as an antioxidant, helping to protect cell membranes and delicate structures like sperm cells from oxidative stress. Your body can make CoQ10, and it is found in small amounts in foods like meat and fish, but levels may fall with age or certain medications. That's why CoQ10 is often studied in the context of heart health, fatigue, and male fertility.