| Many People Get Too
A recent survey Booth conducted in collaboration with the
Proctor & Gamble Company supported what she had seen in an earlier study of
U.S. diets by the vitamin K lab. If you're between the ages of 18 and 44,
there's a good chance you didn't get enough vitamin K todayor any other
She and her colleagues estimated vitamin K intake from 14-day food intake
diaries of a nationwide sample of about 2,000 households.
Phylloquinone, the most common form of vitamin K, was the researchers'
benchmark for vitamin K intake.
"People over age 65 consumed more phylloquinone than those in the 20 to
40 age bracket," she says. Only half the females age 13 and over and less
than half the males got the RDA, she notes. "This confirms there are very
low intakes nationwide."
Booth says recent evidence suggests the current RDA may not be sufficient
for maximizing vitamin K's function in bones. The vitamin adds chemical
entities called carboxyl groups to osteocalcin and other proteins that build
and maintain bone. Exactly how much vitamin K is needed to optimize this
function is still being established.
Phylloquinone is found in some oils, especially soybean oil, and in
dark-green vegetables such as spinach and broccoli. For instance, one serving
of spinach or two servings of broccoli provide four to five times the RDA of
Most of the survey respondents also consumed another form of vitamin
Kdihydrophylloquinoneproduced during the hydrogenation of oils.
About half of U.S. soybean oil is hydrogenated, according to the Institute of
Shortening and Edible Oils in Washington, D.C. The degree of hydrogenation
ranges from light, for margarines, spreads, and cooking oils used in
restaurants, to heavy, for deep frying and bakery products.
Booth says that as much as 30 percent of total vitamin K intake may come in
the form of dihydrophylloquinone, but it is less biologically active than
phylloquinone. In fact, it was half as active with a clot-forming protein and
was completely inactive with a bone-forming protein. "So hydrogenated oils
shouldn't be considered an important source of vitamin K," she emphasizes.
Veggies vs. Oils
What is the best source of vitamin K? Vegetables provide the lion's share of
this vitamin in the diet. But nutritionists have assumed that people absorb
more from oil or oil-based supplements than from vegetables.
To find out, Booth led a study with colleagues at Yale University School of
Medicine to compare the absorption and useknown as
bioavailabilityof vitamin K from broccoli and from oil fortified with the
vitamin. For 5 days each, volunteers consumed a helping of broccoli or
fortified oil along with a base diet. This increased their phylloquinone intake
to around 400 µg/dayfive to six times the RDA.
"What's really exciting," Booth says, "is to look at the
functional markers for vitamin K status. There were no differences between
vitamin K from broccoli and vitamin K from oil overall. That's good because
green leafy vegetables contain so many other nutrients."
For instance, when the volunteers ate broccoli, blood levels of an important
carotenoidluteinincreased compared to when they ate the base diet
Booth says scientists are now using different measures of vitamin K status
because the traditional yardstickblood coagulation timeis not
sensitive enough to detect changes in status. So the researchers relied on
changes in plasma phylloquinone levels and two functional markers.
One functional marker is the bone-building protein osteocalcin. To be fully
active, it must be saturated with carboxyl groups, and that's vitamin K's job.
So the researchers looked for changes in saturation in the osteocalcin. After 5
days of eating broccoli or oil fortified with vitamin K, says Booth, more
osteocalcin was saturated with carboxyl groups.
The second functional markerurinary Gladidn't change. Short for
gamma carboxyglutamic acid, Gla indicates overall vitamin K activity in the
body. Its lack of change was expected, says Booth, because the supplementation
period was short. She has since found that it takes 10 days on the same diet to
cause a change in urinary Gla.
Phylloquinone in blood plasma increased as expected. Booth says changes in
plasma levels help show recent changes in intake. But they are not good markers
of long-term vitamin K status because they fluctuate according to the diet.
Older and Younger Adults Benefit
The study included 18 older men and women and 18 younger volunteers to see
whether bioavailability changes with age. There was no difference between the
20- to 40-year-old group and the 60- to 80-year-old group. This surprised the
"Older people tend to have higher blood levels of phylloquinone,"
explains Booth, "so we thought they might not respond to dietary increases
as much as the younger group."
"Instead, the study showed that older people can get just as much
benefit from increasing vitamin K intake." And that's good news because
there is some evidence that hip fractures may be associated with lower
saturation of osteocalcin.By Judy
McBride, Agricultural Research Service Information Staff.
This research is part of Human Nutrition, an ARS National Program (#107)
described on the World Wide Web at
Sarah L. Booth is at the
Jean Mayer USDA Human Nutrition Research
Center on Aging at Tufts University, 711 Washington St., Boston, MA 02111;
phone (617) 556-3231, fax (617) 556-3149.