How often do we need to consume vitamins? at what doses is good for the body?

1 multivitamin is ok: If a person has knowledge of nutrition and has a very balanced diet, then she may not need to take a daily multivitamin because her foods contain enough. It's often recommended each person take a multivitamin because many people don't have a truly balanced diet. Some people also need extra vitamin D, calcium, folate, omega3, etc., depending on individual needs. Generally there are no side effects.