Manganese is a trace mineral needed in humans for the enzymes prolidase, glucosyl transferase, arginase, superoxide dismutase, pyruvate carboxylase and phosphoenolpyruvate carboxylase. Manganese may also bind to ATP and ADP to prevent cyclic AMP accumulation in cells. Manganese deficiency is thought to be rare in humans, but the extent of sub-clinical insufficiency is not known because manganese metabolism is not fully understood. Absorption and retention of manganese in animals is highly variable and is also affected by age and sex. In humans, estimates of manganese absorption have ranged from 1% to 30%, although manganese can be returned to the gut within an hour through bilary secretion. It is unknown why sex should influence manganese absorption but it may relate to the fact that manganese interacts with other minerals such as iron and the iron status of women is different to that of men.
Researchers1 have investigated the absorption and retention of manganese in 20 men and 20 women aged 18 to 40 years in order to further understand sex differences. Subjects consumed a diet deficient in manganese (3.51mg/Mn/d) for 2 weeks, and were then fed a test meal containing radio-labelled 54Mn in a 240mL juice drink. For 2 weeks, faeces and urine were analysed to assess the absorption and retention of the radio-labelled manganese, and whole body manganese was assessed with a whole-body counter. The results showed that the absorption of manganese in men was lower than in women. However, the manganese absorbed by men had a longer half-life when compared to women. When the study authors analysed plasma ferritin levels, they found a significant association with manganese absorption. There was also an association between manganese absorption and the manganese half-life.
These results suggest that manganese absorption and metabolism differs between men and women, possibly due to the differences in plasma ferritin between the sexes. This supports data from other studies that shows interactions between iron and manganese. As iron status is reduced (to around 30µg/L serum ferritin) iron absorption increases. In this study, the women had a mean serum ferritin levels of 39µg/L, whereas the men had serum ferritin levels of 115µg/L. Therefore the iron status of the individual may be affecting the manganese absorption. Because women absorbed more of the manganese, this may explain the short half-life seen in plasma manganese levels. Male rats have been shown to also have longer manganese half-life times as well as higher liver concentrations of manganese, supporting these findings. These results suggest that manganese and iron interact in human metabolism.
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