B vitamins, a group of 8 different vitamins which collectively are known as B complex, are important because they keep your cell metabolism healthy and working properly. Some foods are high in B vitamins, including milk, whole-grain cereals, nuts, eggs, yogurt, meat, and leafy green vegetables. However, it can be hard to get your recommended daily amount simply from eating these foods, and some people have trouble absorbing B vitamins from food alone. Because of this, it's important to take a B complex supplement and make sure you're not deficient in any B vitamins.