Aim: To determine the concentration of vitamin K including K1 (phylloquinone) and K2 (menaquinone-n; MK-n) in the maternal milk of Japanese women.
Methods: We collected human milk samples from more than 4000 mothers living throughout Japan from December 1998 to September 1999, and analysed the contents of vitamin K1 and K2 in 834 of the samples. We defined as group A the 555 samples among them that met the following conditions: breast milk of mothers who were under 40 y old, not in the habit of smoking and/or using vitamin supplements, and whose babies showed no symptoms of atopy and whose birthweights were 2.5 kg or more. Vitamins extracted from the enzymatic hydrolysates of the human milk were purified with a Sep-Pak Plus silica cartridge, and then measured by a method based on high-performance liquid chromatography (HPLC) combined with coulometric reduction and fluorometric detection.
Results: The mean concentration of vitamin K (K1 + K2) of mothers of group A and all groups were 0.434 +/- 0.293 and 0.517 +/- 1.521 microg/100 ml (average +/- SD), respectively, and menaquinones containing 4, 6 and 7 isoprenoid residues could be detected in the milk samples. Vitamins K1 and MK-4 were found to be predominant in the milk samples, and the concentration of MK-4 in colostrum was higher than that of MK-4 in mature milk. We also found that the MK-7 concentration in the milk of mothers living in eastern Japan was higher than that of mothers living in western Japan.
Conclusion: The different features of vitamin K1 and MK-7 concentrations in the milk of Japanese women may be due to differences in dietary foods.