Although the specific mechanisms for manganese absorption and transport have not been determined, some evidence suggests that iron and manganese can share common absorption and transport pathways (10). Absorption of manganese from a meal decreases as the meal's iron content increases (7). Iron supplementation (60 mg/day for four months) was associated with decreased blood manganese levels and decreased MnSOD activity in white blood cells, indicating a reduction in manganese nutritional status (11). Additionally, an individual's iron status can affect manganese bioavailability. Intestinal absorption of manganese is increased during iron deficiency, and increased iron stores (ferritin levels) are associated with decreased manganese absorption (12). Men generally absorb less manganese than women; this may be related to the fact that men usually have higher iron stores than women (13). Further, iron deficiency has been shown to increase the risk of manganese accumulation in the brain (14).

Supplemental magnesium (200 mg/day) has been shown to slightly decrease manganese bioavailability in healthy adults, either by decreasing manganese absorption or by increasing its excretion (15).

In one set of studies, supplemental calcium (500 mg/day) slightly decreased manganese bioavailability in healthy adults. As a source of calcium, milk had the least effect, while calcium carbonate and calcium phosphate had the greatest effect (15). Several other studies have found minimal effects of supplemental calcium on manganese metabolism (16).