Endurance athletes, including marathon runners, distance triathletes and century cyclists, need optimal nutrition to train and compete at their best. A balanced diet should give you all the vitamins and other nutrients you need, but training schedules, travel for races and lack of personal willpower can mean you don't always consume the best foods for your needs. If you're deficient in certain vitamins, you might feel it in your energy levels and recovery. Whole foods offer the best sources of vitamins, but your doctor may recommend supplements if you're especially deficient.
The B vitamins, B-6, B-12, pantothenic acid, thiamine, biotin, niacin, folate and riboflavin, play an intrinsic role in energy production and cell production. They help you metabolize food and turn it into fuel for your runs, rides and swims. An array of B vitamins is available in fortified grains and breads, and many are also found in nuts and meat, fish or poultry products. If you're a vegan or vegetarian, you are at risk of not getting enough B-12, which if left uncorrected can eventually lead to the lethargy and weakness associated with anemia. Eat dairy foods, like Greek yogurt and nonfat milk, or reach for B-12-fortified vegan milks to avoid a deficiency.
You may know that the sun can help your body produce its own vitamin D, but you can also get this essential vitamin from fortified milk, seafood and eggs. Being out in the sun doesn't guarantee your levels are up to par. Too little vitamin D can make you feel weak and lacking in energy during workouts.
The antioxidant properties of vitamin C help endurance athletes repair the inflammation associated with heavy training loads. Vitamin C also aids in the absorption of iron and folate, two nutrients that help with the production of red blood cells, which deliver oxygen to working muscles.