Human Epidemiological And Casecontrol Studies For Lycopene

Large epidemiological studies have shown that people who eat tomato products experience lower rates of cancer (Weisburger, 1998) and heart disease (Klipstein-Grobusch et al., 2000; Kohlmeier et al., 1997; Kristenson et al., 1997). Many epi-demiological and case-control studies suggest that tomatoes, or lycopene, can delay or prevent certain types of cancers (Giovannuci et al., 1995; Jordan et al., 1997; de Stefani et al., 2000; Palan et al., 1996). Promising results have been found for cervical (Batieha et al., 1993) and breast (Dorgan et al., 1998; London et al., 1992) cancer.

The most studied interaction — and probably the most promising results — are against prostate cancer (Gann et al., 1999; Giovannucci et al., 1995; Hsing et al., 1990; Kristal and Cohen, 2000; Norrish et al., 2000; Rao et al., 1999). Estimates of lycopene consumption in these studies can be better predictors of prostate cancer risk than beta-carotene or total carotenoid consumption. Prostate cancer is a common and increasing medical problem (Carter and Coffey, 1990; Garnick and Fair, 1998), therefore, identifying a phytonutrient that may delay its onset would be useful.

There have been no clinical trials published on lycopene intervention, but several interventions have looked at preliminary biomarkers. For example, studies have reported that tomato consumption increased DNA protection from oxidation (Porrini and Riso 2000); and that tomato juice (Uprichard et al., 2000) or tomato oleoresin, a semipurified source of lycopene, decreased lipoprotein oxidation (Agarwal and Rao,

  1. Other studies have shown no effect from dietary supplements (Dugas et al.,
  2. or tomato consumption (Pellegrini et al., 2000).

The fact that most lycopene in the diet comes from tomatoes and tomato products has had both beneficial and deleterious impact on research. It has been beneficial, because it is probably easier and more accurate to get good dietary intake estimates or food records when only a few foods are important. Furthermore, tomatoes are generally not hidden nutrients, as flour, salt, and sugar might be. Typically, when we eat tomato products we know that they contain tomatoes. Better and easier estimates of dietary intakes should lead to better nutrition research based on these estimates. Although lycopene is found in foods other than tomatoes, these foods are eaten rarely by most people. Substituting tomatoes for lycopene does not give a significantly biased result for people eating typical European or Western diets. Further, tomatoes are eaten by most ethnic groups, and cut across most cultures and lifestyles. For example, eating raw tomatoes in salads is associated with healthy lifestyles, while eating cooked tomato sauce on pizza (a better vehicle for lycopene) is associated with bad diets. So, unlike most phytonutrient-rich foods, tomatoes are probably not a surrogate for a healthy lifestyle, good income, increased education, or health consciousness.

Unfortunately many epidemiological studies have been conducted and reported as if 'tomato' and 'lycopene' were equivalent terms; however, a tomato is a complex entity, not a single phytonutrient. Tomatoes also provide substantial amounts of vitamin C and other carotenoids including beta-carotene, phytofluene, zeta-carotene, gamma-carotene, neurosporene, and phytoene. A recent study demonstrated that phytofluene is more bioavailable than expected based on its concentrations in tomatoes (Paetau et al., 1998). This suggests that phytofluene might play a role in protecting human health. Beta-carotene and vitamin C both have known biological functions. Furthermore, tomatoes are good sources of fiber and potassium. Thus, the functions hypothesized for lycopene from epidemiological studies may actually be associated with an unrelated phytonutrient.

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