According to the World Health Organization (WHO) the most common vitamin deficiency in the whole world is iron or vitamin B6 deficiency with an estimated 700 million people suffering from it. Vitamin B6 deficiency would lead to a whole bunch of conditions such as anemia, fatigue, seizures, and in some rare cases, depression. It is mostly the brain that will suffer from lack of Vitamin B6 but the blood also takes quite a hit if the body does not have enough iron in it.