Do carotenoids--the bright red, yellow and orange pigments in fruits and vegetables--warrant a Recommended Dietary Allowance? New findings about the thyroid and oxidation could bring researchers closer to answering this question. Two ARS experiments with female volunteers examined effects of meals low in carotenes. The experiments--one lasting the 14 weeks and the other 17 weeks--were the longest and most rigidly controlled low-carotene studies using human volunteers. About a dozen women participated in each study. Thyroxine, a key thyroid hormone, increased when the women ate few carotenes or other carotenoids at mealtimes. The finding adds to the few previously known links between carotenes and the thyroid. Researchers also found more evidence suggesting carotenes act as antioxidants to protect the body from harmful oxidation. Antioxidants are thought to help prevent heart attack, stroke and cancer. During the low-carotene stints, researchers recorded several biochemical signs of oxidative damage. For example, they found more carbonyl compounds--breakdown products of oxidation--in the volunteers' blood and breath. The scientists apparently were the first to note these changes in humans in a carotenoid study that featured familiar foods. Later experiments elsewhere found similar results. Further ARS studies will try to shed more light on whether a specific minimum daily intake of carotenoids is important for good health.
Western Human Nutrition Research Center, San Francisco, CA
Betty J. Burri, (415) 556-6285

Older people who get plenty of beta carotene may have a better chance of preventing virus infections or a cancerous growth. A wealth of epidemiological evidence has linked a high intake of green leafy and deep yellow vegetables--both rich in beta carotene--with lower rates of many types of cancer. But recent studies found a higher rate of lung cancer in smokers who took beta carotene supplements. And the supplements did not meet expectations for reducing cancer incidence in the 12-year-long Physicians Health Study led by Harvard researchers. The elderly may be an exception, however. Men over age 65 who took a 50-milligram beta carotene supplement every other day during the 12-year study had natural killer cells that were more active than their counterparts who got a placebo. Natural killer cells--or NK cells--are the immune system's sentinels, ever on watch for viruses and cancer cells. They recognize an enemy immediately and destroy it, using proteins to punch holes in its outer membrane. This activity is thought to be an important component of cancer prevention. So ARS researchers tested NK cell activity in 59 men in the physician study. Thirty-eight were middle-aged--51 to 64 years--and 21 were elderly--65-86 years. NK cells from the middle-aged men killed cancer cells at about the same rate whether they got beta carotene or the placebo. Among the elderly men, however, the placebo group's NK cells were significantly less active, while the supplement group's cells kept pace with the middle-age group. The beta carotene dosage used in the physicians study is equivalent to eating two regular-size carrots or 1.5 sweet potatoes daily.
Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, Boston, MA
Simin Nikbin Meydani, (617) 556-3129, s_meydani_im@hnrc.tufts.edu

Ounce for ounce, blueberries, Concord grape juice, strawberries, kale and spinach had the most potent antioxidant activity of 40 fruits, juices and vegetables measured in a "test tube" assay. Health professionals believe that oxygen free radicals, generated by the body's own metabolism as well as environmental pollutants, cause wear and tear on DNA and other cell parts that leads to cancer, heart disease and other diseases of aging. Eating foods that help prevent oxidative damage could enhance health and extend life. So ARS researchers measured the total antioxidant capacity of common fruits, juices and vegetables by an assay known as ORAC--Oxygen Radical Absorbance Capacity. Animal studies on the top-scoring foods are now in progress to see if the ability of these foods to disarm oxygen free radicals in the "test tube" translate to the human body. If so, the advice to eat more fruits and vegetables, particularly berries and greens, takes on added importance. For instance, 3.5 ounces of blueberries--about two-thirds of a cup--had the same antioxidant capacity in the ORAC assay as 1,773 International Units (IU) of vitamin E or 1,270 milligrams (mg) of vitamin C. Blueberries, by far, had the highest antioxidant score of the tested fruits and vegetables purchased in groceries. But scores could vary widely based on growing conditions, season and many other variables in different parts of the country. Concord grape juice had two-thirds the potency of blueberries, and strawberries were about half as potent. Among the vegetables, kale scored a little higher than strawberries, and spinach scored somewhat lower. The ORAC assay is a unique test of total antioxidant capacity in that it measures the degree to which a sample inhibits the action of an oxidizing agent and how long it takes to do so. The researchers are working with equipment manufacturers to develop an instrument for wide application of the assay in analyzing food, blood and other types of samples.
Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, Boston, MA
Ronald L. Prior/Guohua Cao, (617) 556-3310/3141, prior_us@hnrc.tufts.edu cao_am@hnrc.tufts.edu

Chicken drumsticks are giving boron a leg to stand on as an important element for optimum bone growth. Studies of growing chicks show that boron--found mostly in fruits, vegetables, legumes and nuts--can partially compensate for a low vitamin D intake in bone formation. Like human children, chicks raised on a diet deficient in vitamin D develop rickets, a bone deformity in which the actively growing ends, or growth plates, are weak from lack of minerals. Adding boron to the vitamin D-deficient diet significantly improved the accumulation of minerals in the chicks' growth plates. They added several levels of boron to the chicks' diets to approximate the range people might get through typical diets. After four weeks, they inspected the growth plates under a microscope. Those closest to normal came from chicks getting the highest level of boron--4.2 milligrams per kilogram of feed. This is equivalent to the boron levels in a human diet containing plenty of fruits and vegetables. Even in the chicks raised on diets containing adequate vitamin D, the growth plates tended to mineralize better when the animals got ample boron.
Grand Forks Human Nutrition Research Center, Grand Forks, ND
Curtiss Hunt, (701) 795-8423, chant@gfhnrc.ars.usda.gov

Daily servings of dark green and deep yellow vegetables and tomatoes boost immune response, a preliminary study suggests. If the findings hold up in further research, eating more vegetables rich in beta carotene and related carotenoids--lutein and lycopene--may help people ward off a cold or flu as well as protect against cancer. The researchers wanted to know if people could increase their blood levels of these carotenoids by eating "acceptable" portions of carotenoid-rich vegetables. So 12 volunteers lunched daily on five servings of cooked kale and sweet potato and washed it down with tomato juice--together providing 10 times more than typical U.S. carotenoid intakes. After three weeks, the volunteers had a 33 percent increase in immune response as measured by the ability of their T cells to multiply. This is a good measure of immune system function because T cells play a vital role in its response to foreign organisms and cancer cells. The veggie lunches also more than doubled blood levels of beta carotene and increased lutein by 67 percent and lycopene by 26 percent. Sweet potato is rich in beta carotene, while kale and tomato are top sources of lutein and lycopene, respectively. As potent antioxidants, these carotenoids are thought to contribute to the lower rates of heart disease, cancer and other diseases of aging among populations that eat a lot of fruits and vegetables. The findings suggest that carotenoid-rich vegetables also stimulate the immune system. But other tests done during the study failed to show any reduction in oxidation of blood lipids or damage to DNA molecules.
Beltsville Human Nutrition Research Center, Beltsville, MD
Tim R. Kramer/Beverly Clevidence, (301) 504-8459/-8367, kramer@307.bhnrc.usda.gov; bev@bhnrc.arsusda.gov

Secrets about the way our bodies absorb and use fats and two essential vitamins might be revealed by experiments with a unique strain of laboratory mice. Researchers with ARS and the University of California at San Francisco have bred mice that don't correctly absorb fats and vitamins A and E that we store in fat. The mice are the first of their kind. While healthy in other ways, they don't form a molecule called apolipoprotein B in their intestines, where it is needed to take up fat. The scientists showed that the mice had slightly low concentrations of vitamin A in their blood and extremely low levels of vitamin E. We require these vitamins for normal eyesight, brain function and health. Further tests using the mice might help researchers determine why some people absorb vitamins A and E much less efficiently than others. Once nutrition and health-care professionals know what factors to look for, they could alert individuals before vitamin deficiencies appear. This information could also enable adjustments in USDA-administered food assistance programs, to ensure that the recipients' needs for vitamin A and E are met.
Western Human Nutrition Research Center, San Francisco, CA
Betty J. Burri, (415) 556-6285

One or two alcoholic drinks a day can interfere with people's B vitamin levels, according to a study of 41 men and women. Blood levels of vitamin B12 dropped when the volunteers consumed five percent of their daily calories as alcohol. Compromising B12 status, over the long term, could impair memory, giving the impression of senility where there's no disease. Most Americans get ample B12 because it is in animal products, including eggs and dairy foods. That's not true for folate which is supplied by dark, leafy green vegetables--such as spinach, broccoli and collards--and citrus fruits and juices. Although folate levels didn't drop with alcohol consumption, they rose significantly during the alcohol-free period. This supports other evidence that the Recommended Dietary Allowance (RDA) for folate is too low because the volunteers were given the RDA in their test diets. Another indicator that moderate alcohol consumption interferes with vitamin B12 and folate was a drop in homocysteine levels during the alcohol-free period. When people don't have enough of these vitamins to metabolize homocysteine, it accumulates in the blood and damages the vessels. Elevated levels of this amino acid have recently been recognized as a risk factor for cardiovascular disease. The findings also help to settle a long-standing debate over the cause of low B vitamins in alcoholics. Some health professionals argue that it is due to alcoholics' poor nutrition, while other attribute it to the alcohol degrading the vitamins. Both factors appear to contribute.
Beltsville Human Nutrition Research Center, Beltsville, MD
Judith Hallfrisch, (301) 504-8396, hallfris@asrr.arsusda.gov

Researchers are exploring whether rice starch can be altered to slow its digestion--important news for diabetics who want to keep their blood sugar levels stable as food is broken down in the digestive process. Another potential target audience: marathon athletes who need a steady flow of "fuel" during long periods of exercise. Slow-digesting rice starch is created using enzymes and heat. The altered rice starch also might serve as a fat replacer. It can be made in consistencies ranging from a liquid to a thick cream. This product would provide a new use for broken rice kernels that typically sell for about 7 cents per pound, compared with 24 cents for unbroken kernels, and often wind up in pet foods rather than human food.
Food and Feed Processing Research, New Orleans, LA
Harmeet Guraya, (504) 286-4258

Teenage mothers don't meet the nutritional needs of their infants through breast feeding alone and rely on formula to supplement. That's what researchers found when they compared the quantity and quality of breast milk and the breast-feeding behavior of 11 teen mothers with 11 adult mothers during the first six months after delivery. Nutritionally speaking, the teens' breast milk was about equivalent to the adults' breast milk in calories, sugar (lactose), fat, protein and the major minerals. But the amount of milk produced by teen moms was one-third to one-half lower than that of the adult moms. Also, the teens did not nurse as long or as often as the adult moms. It's not known whether this behavior is the cause or the result of teens' lower milk production. But the result was that teen moms fed their babies more formula to supplement the lack of breast milk. Education and support aimed at increasing teens' daily nursing duration might improve production and reduce the need for formula, researchers say.
Children's Nutrition Research Center, Houston, TX
Kathleen J. Motil, (713) 798-7180, kmotil@bcm.tmc.edu

Rats whose laboratory diets were deficient in copper or magnesium were hyperactive and had either learning or memory deficiencies, suggesting that these two essential minerals may affect human behavior. Researchers tested the psychological impact of each mineral because previous experiments have shown both have important roles in brain function. In one study, they fed rats diets containing either adequate copper or about one-tenth the adequate level for 10 weeks. In a second study, they altered the magnesium content of the diets in the same manner. Deficiencies of both minerals prompted the rats to be more active in general. That's consistent with symptoms of magnesium deficiency in people who often experience tremors and disrupted sleep. The animals also turned in circles incessantly, similar to people who exhibit obsessive behaviors. The magnesium-deficient rats circled spontaneously, while the copper-deficient did it only after being stressed by a loud noise, the researchers reported. Also, copper-deficient rats were slower to learn, and the magnesium-deficient animals had more difficulty remembering than their counterparts who got adequate doses of these minerals. Magnesium is found in a wide range of plant and animal foods, including nuts, whole grains, green leafy vegetables, meat, fish and poultry and dried fruit. The richest source of copper is oysters.
Grand Forks Human Nutrition Research Center, Grand Forks, ND
James G. Penland, (701) 795-8471, jpenland@gfhnrc.ars.usda.gov

Eating more fruits, vegetables and cold cereal fortified with folic acid--a form of folate--should significantly reduce the risk of heart disease and stroke that comes from having high blood levels of homocysteine, a new study shows. These foods contribute the most dietary folate, which the body needs to convert homocysteine into a nontoxic amino acid and thus prevent damage to blood vessels. Researchers found an unusually strong relationship between the amount of these foods consumed and blood levels of folate and homocysteine in a study of 855 elderly men and women participating in the Framingham Heart Study. And that's after adjusting the data for age, gender, total calorie intake and the use of supplements containing folate. Study subjects who ate at least five to six servings of fruits and vegetables daily had the highest blood folate levels and the lowest homocysteine levels, as did those who averaged nearly one serving of breakfast cereal daily. Those who ate less than three servings of fruits and vegetables daily and seldom ate cereal had the highest homocysteine levels, the researchers reported. Orange juice and dark green leafy vegetables, such as broccoli and spinach, were the major contributors of folate among the fruits and vegetables. Women's homocysteine levels were lower than men's. Subjects aged 67 to 80 had lower levels than those over 80, despite higher blood folate levels in the latter group. Supplement users had the lowest homocysteine levels, but not much lower than frequent consumers of fruits, vegetables and cereal. This suggests that people of all ages can reduce their health risk substantially simply by changing their diet. That's especially important for the elderly, who tend to have low folate status.
Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, Boston, MA
Katherine L. Tucker, (617) 556-3351, tucker@hnrc.tufts.edu

Last Updated: January 28, 1997
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