Objective Molybdenum (Mo) and chromium (Cr) are essential trace elements in human nutrition. Since there are no available information on Mo and Cr contents of breast milk in Japanese, Dietary Reference Intake in Japan has not set Adequate Intakes (AIs) of Mo and Cr for infants. In the present study, to estimate AIs of Mo and Cr for Japanese infants, we determined the both elements in breast milk samples from Japanese women.

Methods Seventy-nine breast milk samples were collected from Japanese women in Kyoto, Hokkaido, Nagasaki, Hiroshima and Kanagawa Prefectures. Mo and Cr in breast milk were determined by inductively coupled plasma mass spectrometry.

Results At the case of Mo, 51 samples showed values of less than 5 ng/ml as Mo content and only 12 samples showed values of more than 10 ng/ml. Minimum, maximum, mean, standard deviation, geometrical mean and median of the Mo were 0.04, 25.91, 5.42, 5.33, 3.55 and 3.18 ng/ml, respectively. At the case of Cr, 38 samples showed values of less than 1 ng/ml, 20 samples showed values of 1 to 2 ng/ml, and only 6 samples showed values of more than 5 ng/ml. Minimum, maximum, mean, standard deviation, geometrical mean and median of the Cr were <0.02, 18.67, 1.72, 2.57, 0.54 and 1.00 ng/ml, respectively.

Conclusions When using the geometrical mean values, AIs of Mo and Cr for Japanese infants were estimated to be 2.8 and 0.4 microgram/d, respectively.