Forever and ever! Unless you are totally organic, your body is not getting what it needs in the every day foods you eat. If you are totally organic, you are still not getting what you need due to depleted soil. I take multivitamin every day and have had very few health challenges this year. It works for me.
I take supplements and it's made a difference in the way I feel and the amount of illnesses I've had. I take a lot of Vitamin C too since it's a water based vitamin and the body excretes what it doesn't use.