More on the vitamin A/osteoporosis connection: margarine and vitamin K - Literature Review & Commentary - Brief Article

Townsend Letter for Doctors and Patients,  July, 2002  by Alan R. Gaby

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During the hydrogenation of phylloquinone (vitamin K1) rich oils (such as soybean and canola oil), phylloquinone is converted to its hydrogenated form, dihydrophylloquinone. The mean intake of dihydrophylloquinone by US adults is approximately 20 mcg/day, or about 20% of the total vitamin K in the diet. To determine whether the hydrogenation of vitamin K affects its biological activity, 15 healthy men and women consumed a phylloquinone-restricted diet (10 mcg/day) for 15 days and were then randomly assigned to a 10-day repletion period with 200 mcg/day of either purified phylloquinone or dihydrophylloquinone. After a washout period of at least 4 weeks, they underwent the same vitamin K depletion protocol and were then repleted with the alternate supplement. There was an increase and subsequent decrease in measures of bone formation (p = 0.002) and resorption (p = 0.08) after phylloquinone restriction and repletion, respectively, but dihydrophylloquinone had no effect on measures of bone formation and resorpti on. In addition, the absorption of dihydrophylloquinone was less than that of phylloquinone. These results indicate that dihydrophylloquinone is not as well absorbed as phylloquinone, and also lacks vitamin K activity, at least where bone formation and resorption are concerned.

Comment: In the April 2002 issue of the Townsend Letter, I discussed the controversy concerning whether modest increases in vitamin A intake can promote the development of osteoporosis. I pointed out that vitamin A intake, in today's vitamin A-fortified, processed-food environment, is a marker for the consumption of processed foods such as margarine and sugary breakfast cereals. I suggested that the trans-fatty acids in margarine, rather than the added vitamin A, might have an adverse effect on bone. The results of the present study suggest that the consumption of margarine and other sources of hydrogenated vegetable oils may promote bone loss through an additional mechanism; namely, the destruction of vitamin K. This study strengthens the notion that consuming partially hydrogenated vegetable oils is not a good idea, whereas modest increases in dietary vitamin A intake probably do not cause osteoporosis.

Booth SL, at al. Effects of a hydrogenated form of vitamin K on bone formation and resorption. Am J Clin Nutr 2001;74:783-790.

COPYRIGHT 2002 The Townsend Letter Group
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