what nutrient delivers oxygen to the body through the bloodstream and can be found in meat, seafood, whole-grain products and dark leafy vegetables?

Vitamin B Complex
These vitamins play a crucial role in metabolism, provides with energy, red blood cells production and carries oxygen throughout your body. Sources: Whole grain cereals, seafood, poultry, eggs, meat, dairy products, peas and green leafy vegetables.
Hope it helps :)