Introduction

For many years it has been known that there is a relationship between chronic high salt intake and increased risk of gastric cancer. Stomach cancer is the fifth most common cancer worldwide, with 952,000 new cases in 2012 (1). Stomach cancer has a poor prognosis, with the 5 year survival rate being just 15%.(3)

The bacterium Helicobacter pylori is the major risk factor for stomach cancer, as it can lead to inflammation and gastric ulcers which can progress into stomach cancer, (4,5) and salt has been found to increase the action of H. pylori.(4,7)

Symptoms of stomach cancer may include indigestion, lack of appetite, a feeling of fullness, bleeding, blood in the stools, blood clots, pain and/or sickness.

Who is at risk of Stomach Cancer?

Men are at a greater risk of stomach cancer than women. Stomach cancer is most common in the over 55s with less than 8% of cases being diagnosed before this point.(3) People in the most deprived social groups are also at a greater risk.(6) Not all cases involve an infection with H. pylori, however those who have the infection are at a greater risk of stomach cancer.

How does Salt Contribute?

Studies have shown that a chronic H. pylori infection is closely associated with salt intake (Fig 1).(7,8,9) Salt has been found to increase the growth and action of H. pylori, thus increasing the risk of cancer.(4,7) Salt may also act as an irritant/inflammatory agent of the stomach lining, which can expose it to carcinogens.(10,11)

A recent meta-analysis of 7 prospective studies by D’Elia et al, demonstrates a relationship between increasing salt intake and risk of gastric cancer.(12)  270,000 individuals were followed up over 6-15 years and those with high salt intakes had a 68% higher risk of developing gastric cancer than those with low intakes. Similarly, a 2007 meta-analysis of cohort studies found that for every gram of salt intake per day, the risk of developing stomach cancer increased by 8%.(13)

An earlier study looking at deaths from stomach cancer among 39 populations from 24 countries found a significant and direct association between salt intake and stomach cancer deaths (Fig 2).(14) Countries that have a high salt intake tend to have higher numbers of people dying from stomach cancer, posing a major public health problem for countries with have high salt intakes such as Northern China, Japan and Korea. In Japan, where cancer of the stomach is the most common cancer, a positive correlation between salt intake and stomach cancer incidence in different geographical regions has been found.(9) A higher risk of stomach cancer has been found in people who have a preference for salty food including salt-preserved meat and fish.(15)

A reduction in salt intake may reduce H. pylori infection and therefore significantly reduce the risk of developing stomach cancer.(16)

Current Salt Intake & Dietary Advice

Worldwide, almost everyone eats too much salt. The daily recommended maximum is no more than 5 grams a day and yet many countries consume 9-12 grams a day - more than double the recommended maximum.

People with, or considered at risk, of stomach cancer should take special care when shopping to ensure that they buy low salt versions of their favourite foods. This can be done by looking at product labels in store. Foods such as cured meat, bread, cheese and table sauces should be eaten in moderation and no salt should be added during cooking or at the table.

References

1. World Cancer Research Fund (WCRF) (2016) Diet, nutrition, physical activity and stomach cancer  http://wcrf.org/sites/default/files/Stomach-Cancer-2016-Report.pdf?utm_source=wcrfuk&utm_medium=reducingriskpage&utm_campaign=CUPStomach (accessed 09/05/2017)
2. Parkin DM. Cancers attributable to dietary factors in the UK in 2010 IV. Salt. British Journal of Cancer. 2011. 105. S31-S33
3. Cancer Research UK. Cancer Statistics. 2009 http://info.cancerresearchuk.org/cancerstats/types/stomach/incidence/ [accessed 04/08/09]
4. Wang X et al. Stomach  cancer in 67 Chinese counties: evidence of interaction between salt consumption and helicobacter pylori infection. Asia Pacific Journal of Clinical Nutrition. 2008;17(4),644-650
5. Wang C et al. The Association between Helicobacter pylori infection and early gastric cancer: a meta-analysis. The American Journal of Gastroenterology. 2007;102,1789-1798
6. Quinn, M., et al. Cancer Trends in England & Wales 1950-1999. Vol. SMPS No. 66. 2001: TSO
7. Beevers DG et al. Salt intake and Helicobacter pylori infection. Journal of Hypertension. 2004; 22,1475-1477
8. Forman D et al. Association between infection with Helicobacter pylori and risk of gastric cancer: evidence from a prospective investigation. British Medical Journal. 1991; 302,1302-1305
9. Tsugane S. Salt, salted food intake, and risk of gastric cancer: Epidemiologic evidence. Cancer Science. 2005;96(1), 1-6
10. Lambert R & Hainaut P. Epidemiology of oesophagogastric cancer. Best Practice & Research. Clinical Gastroenterology. 2007; 21(6),921-945
11. Shikata K et al. A prospective study of dietary salt intake and gastric cancer incidence in a defined Japanese  population: The Hishayama study. International Journal of Cancer. 2006;119,196-201
12. D’Elia L Rossi G, Ippolito R, Cappuccio FP, Strazzullo P. Habitual salt intake and risk of gastric cancer: a meta-analysis of prospective studies. Clinical Nutrition. 2012. Available online: 30th January 2012
13. World Cancer Research Fund (WCRF) Panel (2007) Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective. World Cancer Research Fund: Washington, DC
14. Joossens JV et al. Dietary salt, nitrate and stomach cancer mortality in 24 countries. European Cancer Prevention (ECP) and the INTERSALT Cooperative Research Group. International Journal of Epidemiology. 1996; 25,494-504
15. Strumylaite L et al. Salt preserved foods and risk of gastric cancer. Medicina (Kaunas). 2006; 42(2), 164-170
16. Kurosawa M et al. Highly salted food and mountain herbs elevate risk of stomach cancer deaths in a rural area of Japan. Gastroenterol Hepatol. 2006; 21(11), 1681-1686
17. Nagata C et al. Sodium intake and risk of death from stroke in Japanese men and women. Stroke. 2004; 35,1543-7