Betty J Burri, PhD, is a research chemist who studies vitamin A and carotenoid metabolism and functions. Dr. Burri received a BA in Physiology at
Dr. Burri has current projects on the metabolism and functions of carotenoids, especially beta-cryptoxanthin, a carotenoid that forms vitamin A. Beta-cryptoxanthin is an antioxidant, and it forms vitamin A, an essential nutrient. Vitamin A is necessary for normal eyesight, growth, development, and immune status. The best sources of beta-cryptoxanthin in the diet are orange fruits, such as mandarin oranges, oranges, and papaya.
There are more than 600 carotenoids in nature, but Dr. Burri focuses on a few that are physiologically important: beta-carotene, alpha-carotene, lycopene, and beta-cryptoxanthin. Her laboratory also emphasizes the use of whole fruits and vegetables, instead of chemically pure vitamin supplements and placebos, in nutrition research.
Dr. Burri is also leading several studies that explore the impact of carotenoid-rich foods on vitamin A status and vitamin A deficiency. Vitamin A deficiency is not common in the
Dr. Burri currently has a study to measure the effectiveness of interventions with orange-fleshed sweet potatoes or mandarin oranges on carotenoid and vitamin A concentrations in breast-feeding women with low vitamin A status. This study is in collaboration with Kazi Jamil the International Centre for Diarrhoeal Disease Research,
Beta-carotene as an antioxidant
Beta-carotene is an important phytonutrient because it is the major source of vitamin A for most of the people in the world.
· Carotenoid depletion decreased antioxidant activity in healthy men and women, but that low physiological concentrations of beta-carotene—the equivalent of one or two servings of vegetables per day--were all that was needed to normalize activity.
· High doses of carotenoids (that were provided as vitamin supplements) did not improve antioxidant activity.
· These results can explain why most epidemiological studies show that eating fruits and vegetables that are good sources of carotenoids are good for you, reducing the risks for chronic diseases; but most clinical trials show little benefit and a potential for harm with high dose supplements.
How beta-carotene forms vitamin A
} Used tiny dose of radio-labeled vitamin A (1 nCi, so low that it is not viewed as being radioactive)
} Measured by accelerator mass spectrometry, which uses a nuclear accelerator to separate and count radioactive carbon atoms
· Apparently similar people absorb beta-carotene quite differently.
· Some otherwise healthy people do not absorb beta-carotene well, which means that they would have to eat more fruits and vegetables—or eat more vitamin A-rich foods—to meet their vitamin A requirement.
· Beta-carotene forms retinyl esters (the storage form of vitamin A) rapidly, and these esters appear in the blood before retinol (the most common form in the blood). This means that we have to measure both retinol and retinyl esters to get a good estimate of how well beta-carotene forms vitamin A.
Vitamin A metabolism
· DGAT1 was the first enzyme identified as an ARAT (acyl retinol acyltransferase)
· It appears to be the most common ARAT, accounting for most of the ARAT activity in the body.
· ARATs are responsible for one pathway of vitamin A metabolism, so identifying DGAT as an important ARAT means that we can find out why some people absorb and store vitamin A much better than others.
Substituting Tangerine for common red tomatoes in the human diet to increase lycopene concentrations
Lycopene is a carotenoid that has been linked to prostate cancer prevention.
The major source of lycopene in the diet is tomatoes, so some men have tried to increase their lycopene consumption to help delay the onset of prostate cancer. However, making a major dietary change is difficult, and some people are allergic to tomatoes. So it would be good to increase lycopene consumption without also increasing tomato consumption. One way of doing that is to increase the lycopene concentrations in tomato, but lycopene is not absorbed well in the body. So another good way is to increase the amount of lycopene that is absorbed from tomatoes. Lycopene in most tomatoes is in a straight-chain (trans) form. However, lycopene in an heirloom variety of tomatoes—the tangerine tomato—is in a bent-chain (tetra-cis) form. Cis-lycopenes are easier to absorb than trans-lycopene, so Tangerine tomatoes (that are rich in tetra-cis lycopene) should be better sources of lycopene than common red tomatoes. They are.
Tomato intervention study design
n Human study, 24 adults (half men, half women).
n Randomized cross-over design, ‘double blind’ with one week treatments and one week washouts.
n Each person ate 300 gm red or Tangerine tomato sauce per day served as chili with salad and bread.
n Red and Tangerine tomato chilies had similar look, feel, and taste. They could be identified only by side-by-side comparison.
n Tangerine tomato chili contained less total lycopene than red chili. It was processed in house and lost more lycopene than expected.
n Red and Tangerine tomatoes increased lycopene and improved antioxidant status.
n Tangerine tomatoes improved lycopene and antioxidant status more than red tomatoes.
Changing plant varieties to improve nutrition
n Pluses: Substituting plant varieties is a simple, acceptable food substitution for people. They often can’t tell the difference. This minor change in diet worked: lycopene and antioxidant status improved.
n Minuses: Substituting varieties is still a complex substitution with sometimes unanticipated results. The Tangerine tomato chili did not have as much lycopene as anticipated, or as much as the red chili. This could happen in other food substitutions.