納豆の少量摂取における血中ビタミンKの変動について

抄録

Patients on oral anticoagulant therapy present a clinical problem when they take large amounts of natto, because immoderate ingestion of natto results in reduction of the effect of warfarin so that thrombotest and PT-INR are adversely affected.
We previously demonstrated an undesirable effect of immoderate ingestion of natto in a trial in patients given 100g of natto each. In the present study changes in blood levels of vitamins K were determined after the administration of reduced doses of 10 and 30g of natto.
There was no change in blood levels of MK-4. Howevere, the blood levels of vitamin K₁ increased from 0.53±0.26ng/ml to 0.72±0.25ng/ml at 4 hours after the administration of 10g of natto (p<0.001). After the administration of 30g of natto the blood level of vitamin K₁ increased from 0.46±0.28ng/ml to 0.70±0.21ng/ml at 4 hours (p<0.001). The blood level of MK-7 increased from 0.58±0.15ng/ml to 2.43±0.77ng/ml at 4 hours, 1.66±0.69ng/ml at 24 hours, and 1.28±0.46ng/ml at 48 hours after the administration of 10g of natto (p<0.001).
After the administration of 30g of natto the blood level of MK-7 increased from 0.57±0.18ng/ml to 7.24±2.92, 4.53±1.82, and 3.00±1.09ng/ml at the same time points as mentioned above, respectively (p<0.001).
The results of this study suggest the wisdom of discouraging patients on anticoagulant therapy from taking natto, since it may reduce the effect of warfarin, be the amount ingested 30g or 10g insted of 100g.