Can do via diet but
While 4700 mg/day is recommended, the average man gets 3200 & woman 2400 in the US, so some believe 4700 is over-ambitious.
Supps only have 99mg because higher doses irritate stomachs. Beans, greens, potatoes, tomatoes, avocado & fruit are among the best sources. See http://tinyurl.com/k3jfd5r & http://tinyurl.com/yp35vj for more on sources &
and http://tinyurl.com/l6fcw3d for a debate on the RDI.