Requirements: There is no specific RDA for manganese; however, we probably need somewhere from 2.5-5 mg. per day. The average diet contains about 4 mg., depending on manganese soil levels, and intakes from food may range from 3-9 mg. per day. To be safe, I believe that we should get at least 4-5 mg. per day. When we take extra calcium and/or phosphorus, we probably also need extra manganese. However, taking supplemental manganese may decrease iron utilization and storage, so we need to make sure we get enough iron as well.
Since dietary manganese is relatively nontoxic, even 10-20 mg. per day is safe. Multivitamin/mineral supplements usually contain from 2-4 mg., but the amount may range from 1-9 mg. Separate manganese supplements are available in the chelated form or as manganese sulfate or gluconate. These are best absorbed when taken between meals and without other minerals, as these may interact with manganese and reduce its absorption. We should probably limit our intake of additional manganese to 10-15 mg. per day on a regular basis. Up to 50 mg. daily has been used in some research studies without negative effects.