Evidence that the vitamin folate--known as folic acid on supplement
labels--may reduce the risk of colorectal cancer got another boost in a recent
study of rats. As the amount of folate in their diet increased, the number of
rats that developed tumors of the colon and rectum from high doses of a known
carcinogen decreased proportionately. So did the number of tumors per rat. In
the human diet, green vegetables, organ meats and citrus are rich sources of
The second leading cause of cancer deaths in the United States, colorectal
cancer claims 60,000 lives annually. Each year, 150,000 new cases are
diagnosed, and up to 90 percent are thought to be related to diet.
Epidemiological studies by others repeatedly have found more precancerous
growths--or adenomatous polyps--in the colons of people with low folate intakes
or blood levels. They also found the converse: Fewer polyps in the colons of
people with high folate intakes or blood levels.
Looking for a cause-and-effect link, ARS researchers turned to a rat model
in which the colon cells go through precancerous changes similar to those of
humans. One group of rats was given the recommended folate level for rats in
their feed. A second group got four times the recommended level, and a third
group got 20 times the recommended level, while the control group got no
About 70 percent of the control rats developed tumors after being
challenged with high doses of the carcinogen dimethylhydrazine. That dropped to
40 percent of the group given the recommended folate level and to only 10
percent of the group given four times the recommended level. Excessive amounts
of folate, however, did not increase protection. In fact, the group getting 20
times the recommended level tended to have more tumors than the rats getting
four times the requirement. The same pattern occurred for the number of tumors
The findings extend those of an earlier study in which extra folate
protected the colorectal cells of this breed of rats against precancerous
changes after challenge with a much lower dose of the same carcinogen.
For more information, contact Joel B. Mason, (617) 556-3194, Jean
Mayer USDA Human Nutrition Research Center on Aging at Tufts, Boston, MA
Getting enough dietary folate can reduce the risk of heart disease and
stroke, even in those who have a glitch in their genes for converting the amino
acid homocysteine to a less toxic relative. Folate--also known as folic acid or
folicin--activates one of the enzymes that promote this conversion and thus
helps to prevent a backup of homocysteine in the cells, which gets dumped into
the blood stream. Studies indicate that elevated blood levels of homocysteine
increase the risk of cardiovascular disease, apparently by promoting artery
In 1988, a group of Canadian researchers discovered a mutation on the gene
that acts as a blueprint for this enzyme. That mutation produces a less
efficient enzyme. ARS researchers, in collaboration with one of the Canadian
researchers, wanted to know if the enzyme's activity depends on the level of
folate in the blood. So they tested blood samples from 365 people enrolled in
the National Heart, Lung and Blood Institute's Family Heart Study and found
that it did--but only in the subjects who had two copies of the genetic
variant, one on each chromosome.
Twelve percent of the subjects had this double variant, the researchers
reported in Circulation (vol. 93, no. 1). In this double-variant group,
those whose blood folate levels were below the study median--6.8 nanograms per
milliliter--had significantly higher homocysteine levels than the subjects with
only one or no copy of the variant. But those whose folate levels were above
the median had normal homocysteine levels.
This genetic variant is quite common, the study found. Forty-seven percent
of the subjects had at least one copy, while 41 percent had none. It's easy to
get enough folate through the diet. Green vegetables and citrus are rich
For more information, contact Paul
F. Jacques, (617) 556-3322, Jean Mayer USDA Human Nutrition Research Center
on Aging at Tufts, Boston, MA
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Body builders will find no help in a bottle of chromium supplements,
contrary to claims that it boosts strength and muscle mass while reducing fat.
A new, well-controlled study of 36 sedentary young men who volunteered for a
weight training program found what other studies have been reporting: Those who
took an extra 200 micrograms (mcg) of chromium daily gained no more strength or
muscle bulk than those who got a placebo. And none of the men had a significant
change in body fat, even after two months of working out five days per week.
One third of the men took chromium picolinate. Another third took chromium
chloride--an inorganic form of the mineral--for comparison, while the rest got
a look-alike placebo. Their overall strength increased from 28 to 36 percent,
on average, depending on the group. Their scores, however, were not
statistically different from one another because of the wide range of body
types in each group. The researchers concluded in the American Journal of
Clinical Nutrition (vol. 63, no. 6) that the benefits of chromium
supplements on body composition occur only in people with low intakes.
Most Americans consume less than 50 mcg each day--the bottom of the range
thought to be adequate--and may be operating on marginal levels. Because the
chromium content of foods varies, sometimes dramatically, one insurance against
deficiency is to eat a wide variety of foods and choose fortified cereals and
whole grain breads over the more refined products.
The study also found that the men taking chromium picolinate, but not
chromium chloride, showed early signs of iron deficiency in three different
assays of iron status. This suggests that extended use may be detrimental,
especially in women before menopause, and needs further study.
For more information, contact Henry C. Lukaski, (701) 795-8353, Grand
Forks Human Nutrition Research Center, Grand Forks, ND; no e-mail address.
On the positive side, chromium picolinate supplements markedly reduced
blood sugar and insulin in Chinese people with type II diabetes in two to four
months. The most sensitive measure of diabetic control--hemoglobin A1C--dropped
to normal in those taking 1,000 micrograms (mcg) daily. And it was
significantly lower in the group taking 200 mcg daily compared to the group
that got a placebo. The results of this ARS-led study conducted in China are
preliminary and need to be reproduced in this country before chromium can be
recommended for the treatment of diabetes. But they hold promise for the
mineral to be added to current treatments.
Chinese physicians recruited 180 patients with type II diabetes in three
Beijing hospitals and assigned them to three groups of 60 each. One group took
500 mcg of chromium picolinate at two different times daily; another group took
100 mcg twice daily, and the third took a look-alike placebo. All of the
patients produced insulin; none was in an advanced stage of the disease.
The patients getting 1,000 mcg--or 1 milligram (mg)--daily ended the
four-month study with an average hemoglobin A1C of 6.6 percent, compared to 8.5
percent for the placebo group. This is a measure of how much sugar is bound to
hemoglobin, which runs around 6.2 or less in healthy people. Fasting glucose
was down to 129 milligrams per deciliter versus 160 mg/dL in the placebo group
and around 120 mg/dL in nondiabetic people.
Patients getting 200 mcg daily ended the study with a hemoglobin A1C of 7.5
percent--also significantly below the placebo group. But blood glucose was not
significantly lower. Both the high- and low-chromium groups had a significant
drop in plasma insulin. People in the early stages of type II diabetes produce
more insulin than normal because it's less efficient at clearing blood glucose.
Chromium appears to make the self-secreted hormone more efficient. It doesn't
affect injected insulin.
For more information, contact Richard A. Anderson, (301) 504-8091,
Beltsville Human Nutrition Research Center, Beltsville, MD
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Cereals, particularly bran cereals, are among the top sources of chromium,
according to state-of-the art analyses of 40 foods. Of the seven cereals
analyzed, five contained between 10 and 20 percent of the minimum suggested
chromium intake in a one- or two-ounce serving. But a slice of whole wheat
bread or an ounce of toasted wheat bran provides only about one percent of the
minimum, suggesting that much of the chromium in foods is contributed by other
factors and is not intrinsic to the food itself. The high levels in cereals
probably are inadvertently added during fortification with other minerals or
Chromium also may be introduced as a result of processing or handling. One
cup of canned mushrooms had more than 10 percent of the suggested minimum
chromium intake, as did one teaspoon of cocoa powder. But chocolate syrup had
only half as much per serving. Canned whole tomatoes and pineapple slices
scored highest in chromium content in this study, with one cup providing 33 to
43 percent of the minimum suggested intake. Many canned and processed foods are
prepared in stainless steel vessels, which have a high chromium content. This
appears to be a case of good contamination because the body can convert
inorganic chromium to a usable form.
For these analyses, the researcher selected 20 frequently consumed foods
and 20 other foods, including cereals, condiments and snack foods, that were
expected to have higher chromium levels. There are no comprehensive data bases
on the chromium content of foods. And, until a decade ago, analytical methods
for detecting chromium in foods were quite unreliable. Recent advances in
graphite furnace atomic absorption spectrometry, used in this study, provide a
rapid and highly accurate method of detecting the small amounts of chromium in
For more information, contact
Nancy J. Miller-Ihli, (301)
504-8252, Beltsville Human Nutrition Research Center, Beltsville, MD
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Middle-aged women in the military who fail to meet the body fat standard
based on tape measurements now have some data to question their score. In a
study of women between the ages of 40 and 60, the tape measure method
overestimated body fat by nine to 14 percent in some women and underestimated
it by seven to 11 percent in other women compared to underwater weighing--a
long-accepted standard. That's because the equations each branch of the
military uses to estimate body fat from circumference measurements of arms,
legs and abdomen were developed from studies of younger people.
The researchers wanted to know if the equations accurately reflect body fat
in older personnel because service men and women who do not meet the standards
must undergo a weight control program until they lose the excess fat. Failing
that, they can be subject to discharge. The cutoffs for body fat range from 26
percent for all women in the U.S. Marine Corps to 36 percent for women over age
40 in the U.S. Army.
Based on these standards, the Army equation overestimated body fat in the
fewest number of women tested--one out of 52, or two percent of the group. The
Navy equation overestimated body fat most often--in seven of 35 women tested,
or 20 percent. Most of those who met the standards based on tape measurements
also met them in underwater weighing, the researchers reported in Medicine
and Science in Sports and Exercise (vol. 27, no. 7).
The findings point to the need for a larger study to assess and possibly
revise these equations for over-40 personnel. The researchers chose to study
older women first because this group is most underrepresented in the current
equations. But they suspect the equations may also need revision for older men.
For more information, contact
Bathalon, (202) 782-2011, Walter Reed Army Medical Center, Washington, DC
or Virginia A. Hughes, (617)
556-3079, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts,
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The U.S. population gets about 90 percent of its calories, fiber, calcium,
iron, fat, saturated fat and eight other nutrients of public health interest
from 527 foods, according to newly released data from the USDA 1989-91
nationwide food consumption survey. These 527 foods qualify as key foods
because of the amount consumed per capita as well as their nutritional content.
Whole milk is a key food for 13 of the 14 nutrients of concern, and two percent
milk provides 12 of these nutrients in significant amounts. Eggs and cheddar
and mozzarella cheeses contribute 10 or more of the selected nutrients--which
include sodium, cholesterol, vitamin A, carotene, vitamin B6, vitamin C,
potassium and zinc in addition to the six already listed. Like milk, many of
the top key foods, such as white bread and breakfast cereals, are fortified.
ARS nutritionists updated the list of key foods based on results of the
1989-91 nationwide food consumption survey. It is used to prioritize the foods
to be chemically analyzed for the ongoing revision of the electronic nutrient
data bases. To determine which foods contribute at least 80 percent of selected
nutrients, the nutritionists turn to their electronic recipe files to break
down combination foods, such as macaroni and cheese or a fast-food burger, into
their ingredients by percentage. For example, macaroni and cheese is about 39
percent macaroni, 35 percent milk, 16 percent cheese, three percent margarine
and so on. That allows the nutritionists to add all the pasta, milk, cheese,
etc., consumed over the course of a day. They then merge these totals with the
nutrient values for each food. A report on the specific procedure will appear
in an upcoming issue of the Journal of Food Composition and Analysis.
Staffers are now developing a key foods list from survey data collected in
For more information, contact
David Haytowitz, (301)
734-8491, Beltsville Human Nutrition Research Center, Riverdale, MD
Back to Contents
Ticks that transmit Lyme disease to humans may find it deadly to get a free
ride on white-tailed deer. That's because of a new deer feeder dubbed "the
four-poster" and patented by ARS. The feeder gets its name from four
pesticide-loaded rollers that rub tick-killing chemicals on a deer's head and
neck as it sticks its head inside the device to feast on corn. Treated deer
help eliminate ticks from wooded areas rather than leaving the pests behind to
find another host. Because the deer don't eat the pesticide, this method is
safe for use during the October-December hunting season when the majority of
adult black-legged ticks feed on deer. Eliminating adult ticks prevents
egg-laying and another generation.
Pesticides used in the rollers are experimental, but researchers say the
"four-poster" is more effective than fencing deer out of
tick-infested areas. Lyme disease is most prevalent in the Northeast, the upper
Midwest and California. If the studies prove to protect people, individual
states could grant special permits to use pesticides on white-tailed deer.
For more information, contact J. Mathews Pound, (210) 792-0342, U.S.
Knipling-Bushland Livestock Insects Research Laboratory, Kerrville, TX; no
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Test kits to check for antibiotic residues in cow's milk also work well with
goat's milk. Doubts had existed because goat's milk has a higher somatic cell
count and different composition than cow's milk--differences that could affect
the outcome of antibotic residue tests designed for cow's milk. But in a recent
study with milk from 85 goats, commercially produced residue test kits designed
for cow's milk gave only one false positive outcome in 935 tests.
Surveys indicate at least 5 percent of bulk milk shipments have been found
to contain detectable amounts of antibiotics used to treat livestock. This
potential human health hazard led to development of the residue test kits.
For more information, contact,
Max J. Paape, (301) 504-8302,
Immunology and Disease Resistance Laboratory, Beltsville, MD
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Two commercial blueberry varieties produced in Florida hold up well under
irradiation, a treatment that could replace methyl bromide, now used to rid the
fruit of quarantine pests. Methyl bromide, a chemical fumigant, is scheduled to
be banned in the United States in 2001. ARS scientists subjected Climax and
Sharpblue blueberries to low-dose irradiation with only minor effects that
should not affect consumer acceptance, they reported in HortScience
(vols. 29 & 30). Blueberries shipped to some U.S. and export markets must
be certified free of certain quarantine pests. Currently, methyl bromide is the
only approved quarantine treatment for blueberries against the apple maggot,
blueberry maggot and plum curculio.
For more information, contact William R. Miller/Roy E. McDonald, (407) 897-7309, U.S.
Horticultural Research Laboratory, Orlando, FL
Florida-grown sweet potatoes can be given a light dose of irradiation to
control the sweet potato weevil. That's the finding of ARS researchers. Sweet
potatoes are an important crop in the southeastern United States, and an
excellent market awaits in areas where the weevil is not present. But shipment
to weevil-free areas such as California is prohibited unless the product has
been fumigated with methyl bromide, the postharvest quarantine treatment
approved to kill this pest. And that treatment has its limitations: Sweet
potatoes have a shorter shelf life after fumigation, and methyl bromide is
scheduled to be phased out by the year 2001. Irradiation, used as a quarantine
treatment for potato weevils, leaves no residue and does not adversely affect
the taste or appearance of the sweet potatoes, even after they've been cooked.
For more information, contact Jennifer Sharp, (305) 238-9321,
Subtropical Horticulture Research Station, Miami, FL
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