cellular repair and growth. They can be responsible for making your hair and nails look healthy. Other vitamins are vital to the transport of important minerals around your body.
Deficiencies in specific vitamins can manifest themselves in pretty horrific ways. B12 deficiencies, for example, can result in horrific levels of fatigue. This is because B12 is responsible for the transport of iron across your body. So any time you run a B12 deficit you are also running an iron deficit - no matter how much iron you actually consume.
Vitamin D behaves much like a hormone in your body, as it's responsible for ensuring your bone health is optimal due to the great deal of minerals its responsible for transporting. Particularly calcium.
Up until 1935, human vitamin intake has been exclusively relegated to food consumption. That was, up until we discovered the ability synthesize vitamins and extract them from various sources of food.