Health Research Models and Epidemiological Evidence

Table 4 summarizes the various types of evidence that have been used to test the hypothesis that lycopene may have health-promoting or protective properties in man. The ultimate proof of efficacy, which would be long-term controlled intervention studies with clinical diseases and or mortality as the end points, are extremely difficult,

Table 4 Types of evidence being sought, that a nutrient such as lycopene may protect against oxidation-induced or other disease processes

1. Model in vitro systems, e.g., oxygen-derived free-radical trapping in pure chemical mixtures.

2. Tissue (cell and organ) cultures, e.g., reduction of optical opacity development in cultured eye lenses; reduced growth rates or apoptosis in tumor cell cultures.

3. Animal studies demonstrating a reduction of oxidation-induced damage or disease with lycopene supplements or with lycopene-rich foods such as tomatoes or tomato products.

4. Human observation studies using intermediate biochemical markers: e.g., inverse relationships between lycopene intakes or its blood levels and biochemical markers, such as lipid or DNA oxidation products.

5. Studies using pathology-related intermediate markers, e.g., arterial thickening or reduced arterial elasticity; precancerous polyposis, etc.

6. Relationships (without intervention) between tomato intakes or estimated lycopene intakes or lycopene contents of serum, plasma, or tissues (e.g., fat biopsies) and actual disease prevalence or incidence in human cross-sectional, case-control, or prospective epidemiological studies.

7. Intervention studies: lycopene supplements producing a reduction in biochemical markers of oxidation damage or in functional markers, or, eventually, in actual human disease incidence or progression.

expensive, and time-consuming to obtain, and cannot address all possible benefits in a single intervention trial.

The two disease categories that have so far received most attention for possible long-term benefits of lycopene have been the amelioration of cancers and of heart disease. Both benefits are plausible in view of the physicochemical and biological properties of lycopene outlined above, because both categories of disease are characterized by tissue damage, which is thought to be induced or exacerbated by reactive oxygen species in the environment or those generated within the body.

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