Added Salt and Cancer Mortality: Confounding by Smoking

Faeh, David; Rohrmann, Sabine; Puhan, Milo; Braun, Julia

doi: 10.1097/EDE.0000000000000116

Institute of Social and Preventive Medicine (ISPM), University of Zurich, Zurich, Switzerland,

The authors report no conflicts of interest.

Supported by Swiss National Science Foundation (grant no. 32473B-143897) and the Swiss Cancer League (grant no. KFS-3048-08-2012).

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To the Editor:

High consumption of salt may increase the risk of cancer.1 However, it is unclear whether personal variations in salt usage can affect cancer risk. Adding salt to food before or after tasting increases salt consumption. This behavior could be an acquired taste or habit or the result of a decreased salt perception.2 We compared cancer mortality among people who never, occasionally, or always added salt to their prepared meals. Smokers and people with obesity may have altered taste perception, and both characteristics may have a synergistic impact on eating behavior.3 We therefore included these variables in our analyses.

We analyzed data from 17,733 Swiss men and women 16 years and older who participated in the National Research Program 1A (NRP1A: 1977–79), a community health promotion initiative, or the Swiss MONICA (Monitoring of Trends and Determinants in Cardiovascular Disease: 1984–93) population survey, part of an international WHO project. We obtained mortality follow-up information by anonymously linking these data with the Swiss National Cohort, which encompasses all residents of Switzerland enumerated in the national 1990 or 2000 census, as well as data from death and emigration registries through the end of 2008. Linkage success was 94% (NRP1A) and 97% (MONICA).4,5

Information on smoking (never, former, current smoker, with number of cigarettes) and salt habits (never, occasionally, or always adding salt to prepared meals) was obtained with questionnaires at baseline. Body mass index (BMI) was calculated from measured height and weight. Cancer death (n = 1,355) was defined according to the International Classification of Diseases (ICD: 8th revision until 1994 and 10th revision since 1995): ICD-8: 140–239; ICD-10: C00-C99; D00-D48. Cox proportional hazards regression models were calculated.

Those who reported that they always added salt to meals had a 30% (95% confidence interval = 4–62%) higher cancer mortality risk than those who never added salt (Table). People who occasionally added salt also tended to have an increased risk, suggesting dose dependence. Adjustment for smoking substantially weakened this association, while adjustment for BMI had virtually no impact.

In this general population sample from Switzerland, there was a dose-response association between adding salt to a prepared meal and the risk of death from cancer. To some extent, this association was confounded by smoking. People who smoke may have a higher taste threshold than those who do not.2 Smokers may also differ in their health behavior patterns, including less attention to a healthy diet.6 Both salt sensitivity and eating patterns could also vary between normal weight and overweight people,3 although BMI did not appear to confound the salt-mortality association in our data. Our analysis was limited by the fact that salt habits and smoking were self-reported and assessed only once, at baseline. In addition, cancer-specific analyses were not possible due to relatively small number of cancer deaths.

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We thank Dr. Kelly Turner for proof reading. We thank the Swiss Federal Statistical Office for providing mortality and census data.

David Faeh

Sabine Rohrmann

Milo Puhan

Julia Braun

Institute of Social and

Preventive Medicine (ISPM)

University of Zurich

Zurich, Switzerland

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