A multicountry study just published in Nutrients finds that smoking, diets rich in animal products, and alcohol have the strongest correlations with cancer incidence rates. The cancer incidence rates are from 2008 as assembled by the International Agency for Research on Cancer of the World Health Organization.
This study is an ecological study in which incidence rates for the various types of cancer for males and females from 87 countries with high quality cancer incidence rate data as well as all 157 countries with cancer incidence rate data were compared statistically with indices for various risk modifying factors. Dietary supply data were obtained from the Food and Agriculture Organization of the United Nations. Data for various periods back to 1980 were included since there is generally a lag of up to 20 years between dietary changes and peak cancer rates. The animal products index includes meat, milk, fish, and eggs. Lung cancer incidence rates were used as an index for the effects of smoking and air pollution. This index integrates the effect of all factors contributing to lung cancer and other cancers linked to lifetime smoking and is a much better index than a snapshot of smoking rates. Latitude was used as an index of solar ultraviolet-B irradiance and vitamin D production.
For the 87 countries with high quality cancer data, the smoking and animal products indices explained over half of the cancer incidence rates, with alcoholic beverage supply explaining a smaller amount. For males, the smoking index was twice as important as the animal product index, while for females, the animal product index was twice as important. These two factors explained 70% of the variation in all cancer less lung cancer rates between countries. The range for these cancers for males extends from 75 to 300 cases/100,000/year, while that for females extends from 80 to 260 cases/100,000/year.
The results for some specific cancers are interesting.
The types of cancer for which animal products had the strongest correlation include female breast, corpus uteri, kidney, ovarian, pancreatic, prostate, testicular, thyroid cancer, and multiple myeloma. The reason why animal products increase the risk of cancer is most likely since animal products promote growth of the body as well as tumors through production of insulin-like growth factor-I (IGF-I). For example, older Japanese are generally shorter than Westerners while younger Japanese are about as tall as Westerners. The traditional Japanese diet derived 10% of its calories from animal products, primarily seafood. Japan has made the nutritional transition to the Western diet, with 20% of the calories derived from animal products. Rates of cancer types common in Western countries rose considerably in Japan during the past 20-30 years.
The findings regarding animal products extend the results reported earlier. For example, in 1907 a study reported in the New York Times reported that cancer rates were much higher among people in ethnic groups such as Germans, Irish, Scandinavians, and Slavonians, who were considered meat eaters, while cancer rates were lowest for Italians and Chinese, who were practically vegetarians.
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