The epidemiological enigma of gastric cancer rates in the US: was grandmother's sausage the cause?

Much has been written concerning the 'epidemiological enigma' of falling gastric cancer rates in the US. Up until the 1930s gastric cancer was the leading cause of cancer mortality in the US. 1 Today it is eighth. This sharp decline during the 20th century remains an unexplained yet startling phenomenon. 2 The leading theories to explain this change concern the advent of refrigeration and infection with Helicobacter pylori. Refrigeration began in the early 1900s and gained widespread use by the 1950s. As a result the US diet began to include more fresh fruits and vegetables (high in anti-carcinogenic anti-oxidants) and less preserved meats (high in nitrites and carcinogenic nitro-samines). 3 The temporal correlation between refrigeration and gastric cancer rates, however, has not held true for countries such as Japan, where widespread refrigeration noted in the 1960s has not resulted in a gastric cancer decrease. Infection with H. pylori. 4 is currently regarded as the main contender to explain the enigma and studies have demonstrated a causal link between H. pylori infection, chronic atrophic gastritis, and the intestinal type of gastric carcinoma. 5 However, multifactorial causality is likely to be involved and other critical cofactors are yet to be identified. 6 The role of dietary nitrite and N-nitrosamines in the patho-genesis of gastric cancer has remained a matter of debate for over 30 years. 7 N-nitroso compounds are potent carcinogens in primate animal models and result in a variety of tumour types. 8 Such carcinogenic nitrosamines can be formed from the reaction of nitrite with secondary amines under acidic conditions (such as occurs in the human stomach) as well as during the curing process used to preserve meats. 9 Dietary sources of nitro-samines include US cured meats preserved with sodium nitrite as well as the dried salted fish eaten in Japan. 10 One aspect of nutritional epidemiology that has received minimal attention in the medical literature concerns changes in US meat curing practices that occurred in the 1920s. Prior to 1923 the level of nitrite detectable in cured meats was extremely high and variable. During that time meat was cured using potassium nitrate (or saltpetre). The conversion of nitrate (NO 3) to nitrite (NO 2) by nitrate-reducing bacteria during the curing process was responsible for the levels of nitrite found in the meats. 11 Nitrite levels as high as 1400 ppm (1 ppm equals 1 mg/kg) nitrite in frankfurters and up …