TEA AND COFFEE BREWS ARE NOT DIETARY SOURCES OF VITAMIN K1 (PHYLLOQUINONE)

Authors: BOOTH SARAH L - TUFTS-HNRCA; MADABUSHI H T - UNIV CALIF AT DAVIS; DAVIDSON KENNETH - TUFTS-HNRCA; SADOWSKI JAMES A - TUFTS-HNRCA

Submitted to: Journal Of The American Dietetic Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: In a literature review on the dietary sources of vitamin K or phyl- loquinone (an important regulator for blood clotting), we dis- covered large discrepancies in the reported K contents of tea and coffee. We measured the vitamin K content of 14 different varieties of green and black tea leaves and 4 varieties of coffee. We found significant tvariations in the vitamin K content of the dried teas which may be attributed to differences in composition, storage, processing, harvesting, and geographic origin. We also found a large variation in the vitamin K contents of coffee. Instant coffee did not contain appreciable amounts of vitamin K, and decaffeinated coffee contained even less. After brewing, the vitamin K content of the tea leaves was lower, but not significantly, than in the dried state. Coffee after brewing was found to have a significantly lower K content than before brewing. Thus, we concluded that though coffee has a high vitamin K content before brewing, brewed coffee is not a dietary source for vitamin K. In addition, we concluded that any therapeutic effects from tea cannot be attributed to its vitamin K content.

Technical Abstract: The phylloquinone content for 14 types of dried tea leaves was determined by HPLC. The mean phylloquinone content of dried tea leaves is 894+/-336 mcg/100g and corresponds to previously reported values for green and black teas. The amount of phylloquinone found in the tea samples analyzed varied more than 5-fold. This variability was greater than expected and may be a result of the differences in composition of the different teas. Since there were significant differences (p<0.001) between two brands of black tea and two brands of green tea, other factors such as storage, processing, harvesting, and geographic origin may also influence the actual phylloquinone content of tea. Four coffee samples were analyzed prior to brewing and contained from 0.5 to 25 mcg of phylloquinone per 100 g. Instant coffee did not contain appreciable amounts of phylloquinone (25 mcg/100g), and decaffeinated ground coffee grains contained less (3.9 mcg/100g). Although there was a trend toward lower phylloquinone content in the boiled tea leaves than in the dried tea leaves after correction for differences in water content, the differences were not significant. In contrast, the phylloquinone content of the coffee grains following brewing was significantly lower than before brewing (p<0.01). However, the phylloquinone contents of both the tea and coffee brews were 0.03 mcg/100 mL or less. Regardless of the observation that tea leaves and regular ground coffee beans contain high concentrations of phylloquinone, the brew is not a dietary source of this vitamin. If there are therapeutic effects on prothrombin levels associated with the consumption of tea as reported in the literature, it cannot be explained by the phylloquinone present in the liquid brew from tea.