Evidence from Descriptive Studies

In 1981, Doll and Peto made an estimate based largely on descriptive studies that 35% of cancers in the USA may be attributable to dietary factors; but reflecting uncertainty in the sources of data used for this estimate, they noted that the range of possible dietary contribution was from as low as 10% to as high as 70%. The marked variation in the rates of most cancers among countries is evidence that dietary factors may influence the development of cancer. The potential range of dietary factors that may influence cancer risk are presented in Table 1. Despite the fact that descriptive studies provide an excellent source of hypotheses, it is necessary to conduct analytical studies to collect data that will provide more definitive evidence.

Table 1 Examples of suspected dietary factors influencing cancer risk

Dietary factor

Site of cancer

Increased risk

Overnutrition/Obesity

Endometrium, gallbladder, breast,

colon

Alcohol

Liver, oesophagus, larynx,

pharynx, breast, colon

Beer

Rectum

Fat (especially saturated)

Colorectum, breast, prostate

Red meat

Colorectum

Salt

Stomach, nasopharynx

Heterocyclic amines

Colorectum

(from cooked meat)

Decreased risk

Fiber

Colorectum, breast

Vitamins A, C, E

Many sites

Protease inhibitors

Colorectum

Calcium, vitamin D

Colorectum

Folate

Colorectum

Lycopene

Prostate

Carotenoids

Lung

Phytooestrogens

Breast

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