Phytochemical Research at Tufts Nutrition

The mission of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (Tufts Nutrition) is to understand the relationship of nutrition to the aging process and to investigate the many age-related physiological changes that can affect the dietary requirements of older people. Increasing attention is now being devoted to the role of phytochemicals in promoting health and reducing the risk for chronic disease among older adults.

Flavonoids are plant secondary metabolites with antioxidant properties. They occur widely in fruits, vegetables, and beverages such as tea, red wine, and fruit juices. They have been shown to exert a range of biological activities, including anti-atherosclerotic, anti-inflammatory, anti-tumor, anti-thrombogenic, and anti-viral effects and may also work to enhance immune responsiveness. Carotenoids function in plants as accessory pigments in photosynthesis and protect against photosensitization in bacteria, plants, and animals. Many epidemiological studies have shown an inverse correlation between consumption of foods rich in these phytochemicals and mortality from cancer and coronary heart disease. In addition, several studies have linked certain carotenoids and flavonoids with roles in visual function.

Tufts Nutrition’s Antioxidants Research Laboratory is exploring the effect of antioxidant polyphenols, particularly the flavonoids, on changes in oxidative stress status associated with aging and chronic conditions such as diabetes, heart disease, and age-related macular degeneration (AMD). Lipid, protein, nucleic acids, and other cellular targets of oxidative damage are being assessed in experimental models and human studies to elucidate antioxidant requirements for optimal health. In-vitro studies have indicated that some flavonoids have a marked synergistic interaction with vitamin E in reducing selected measures of oxidative stress in human lipoproteins. Current investigations include examinations of the bioavailability and antioxidant capacity of flavonoids in healthy older adults as well as in diabetics. Flavonoids from almonds, bilberry, chocolate, green tea, and/or oats are being tested.

The Laboratory for Nutrition and Vision Research and the Nutritional Epidemiology Program’s epidemiological studies have found that antioxidant vitamins are associated with a reduced risk of the development and progression of cataracts and AMD. These observations are now being extended to associations with carotenoid and flavonoid intakes.

Gastrointestinal Nutrition Laboratory researchers have found increases in macular pigment density in the central area of the retina following consumption of spinach and corn, foods rich in the carotenoids lutein and zeaxanthin. High concentrations of this pigmentation have been linked to a decreased risk of AMD. Studies of gender differences in lutein metabolism have shown a significant negative correlation between adipose tissue lutein concentrations and macular pigment for women, but a significant positive relation for men. Studies are exploring the bioavailability of lutein from egg yolks, vegetables, and dietary supplements as well as the effect of supplemental lutein and docosahexaenoic acid on visual function in the elderly.

The consumption of foods rich in provitamin A has been suggested as a realistic and sustainable means to overcome vitamin A deficiency in less-developed countries. To determine the vitamin A value of plant provitamin A carotenoids, vegetables were grown hydroponically with stable isotopes and fed to volunteers. The bioconversion of carotenes to vitamin A from different foods containing equal amounts of provitamin A carotenoids was found to vary with the vegetable tested. The vitamin A value of beta-carotene from the bioengineered Golden Rice will be examined in a clinical trial. The formulation of other carotenoids was found to affect bioavailability when researchers observed absorption of synthetic lycopene three times higher than lycopene from cooked and pureed tomatoes. Advanced mass spectrophotometric methods are used to determine both intact carotenoids and their various metabolic products from intrinsically labeled food in blood and tissue taken from human subjects.

The Neuroscience Laboratory research has revealed that both aging healthy mice and transgenic mice with mutations important to Alzheimer’s Disease (amyloid precursor protein and presenilin-1) perform better in a series of cognitive function tests when fed a diet containing extracts from blueberry. Mice fed blueberry extract also showed significantly greater neuronal signaling. Anthocyanin flavonoids from blueberry also appear to protect nerve cells in culture from amyloid beta and oxidative stress.

These and related research projects at Tufts Nutrition are helping to define the role of phytochemicals in human health and suggest ways to enhance the value of food products and substantiate improved dietary guidelines.

by JEFFREY BLUMBERG
Associate Director
Jean Mayer USDA Human Nutrition Research
Center on Aging, Tufts University, Boston, Mass.

by KATHLEEN CAPPELLANO
Nutrition Information Manager
Jean Mayer USDA Human Nutrition Research
Center on Aging, Tufts University, Boston, Mass.