Yesterday I listened to the Today programme to hear a report on the supposed link between salt and stomach cancer. The report from the World Cancer Research Fund didn’t really explain how this mechanism worked, nor how the trials established this single incriminating factor, and the presenter did nothing to challenge the findings- presumably because we all ‘know’ how bad salt is for us: http://news.bbc.co.uk/1/hi/health/3370141.stm
Now I’m no apologist for heavily salt-laden processed foods, but I am sceptical of the way salt has been held responsible for a whole barrage of chronic diseases, just as saturated fat has been hung out to dry in the last 50 years.
So, the World Cancer Research Fund says 14% of stomach cancers could be prevented by eating less salt, although I couldn’t find this reference on their website. Interestingly in a kind of ‘factoid’ type leaflet, the WCRF also says ‘Although the number of cases is declining, almost 8,000 people develop stomach cancer in the UK each year. Most of these cases are diagnosed in people aged over 50. Scientists estimate that about half of stomach cancer cases in the UK could be prevented by not smoking, cutting down on salt and eating a healthy diet.’ Ah, so now we have all sorts of variables confounded. AND the anomaly that stomach cancer rates are DECLINING despite us consuming 8.6g salt a day.
So perhaps we are consuming more salt now than ever before? Surprisingly not: our salt intake remains roughly the same as it did in 1957 (American Journal Clinical Nutrition, Sept 2010). This is because we used salt to preserve more of our food- handy when you didn’t have a fridge. We’re eating the same amount of salt but in a different way (i.e. hidden in processed foods).
In the US rates of stomach cancer have also declined from over 400, 000 in 1950-69 to 265, 500 in 1985-2004: yet salt consumption has remained constant at about 3700mg sodium per day (about 9g), for the last 50 years (ibid.)
One of the supposed indisputable facts usually held up to support this hypothesis is rates of stomach cancer in Japan, where salt intake is high (use of miso, pickles, salted fish, salt in fermented foods etc), yet even here there is much more than meets the eye. One big factor is smoking. In the 1960s 80% of the male population smoked, twice as high as in the US. The incidence and death rates of stomach cancer also peaked between 1960 and 1980s. Cancers of the stomach and liver alone accounted for 70% of all male cancer deaths in 1951, declining to 41% by 1996 despite liver cancer’s rise (Journal of Demographic Research, Vol.5, 2002). In Japan the stats show that smoking is in decline, but still 51% of men smoke as opposed to 20% of men in the US.
The other significant factor influencing gastric cancer is the incidence of H Pylori infection. In 2006 the journal Gut compared two cohorts of patients, one British, one Japanese, and found that although the infection was almost equally present in the patients’ symptoms of gastritis, the Japanese patients were at greater risk of a more aggressive strain, demonstrating greater atrophy in the gastric lining and more inflammation. This is a key factor in the predisposition towards stomach cancer. In their article ‘The Cancer Transition in Japan since 1951’, the researchers blame over half of stomach cancer cases on the H Pylori infection, and claim that better hygiene and ‘a general improvement in the standard of living’ has seen stomach cancer rates drop. (Journal of Demographic Research, ibid.)
Even if we take stomach cancer out of the equation, limiting sodium intake to under 1500mg a day (that’s less than a teaspoon) has to help prevent cardiovascular deaths, right? Not necessarily and certainly not if you have normal blood pressure. In 2003 the Cochrane Collaboration, partly funded by the US Dept of Health, reviewed 57 short-term salt-reduction trials and concluded that ‘there is little evidence for long-term benefit from reducing salt intake.’ In 2004, it published a review of 11 longer-term salt-reduction trials. Compared to normal diets, these low-salt diets decreased systolic blood pressure (the top number in the blood pressure ratio) in healthy people by 1.1 millimeters of mercury (mmHg) and diastolic blood pressure (the bottom number) by 0.6 mmHg. As the Scientific American magazine put it, ‘that is like going from 120/80 to 119/79’. The review concluded that such ‘intensive interventions…provide only minimal reductions in blood pressure during long-term trials.’
In fact for people with nervous system disorders and thyroid and adrenal problems, limiting salt like this can do far more harm than good, since they find it difficult to maintain adequate electrolyte levels (charged minerals in the blood) which regulate nerve and muscle function, blood pH and hydration. Drinking tonnes of plain water on top of this deficiency can aggravate hypoglycaemia and make people cold, lethargic and anxious.
My advice? Enjoy real food and salt it as you wish- just make sure you use real Celtic sea salt (which should be grey and moist) or Himalayan rock salt, which- unlike table salt- contains the whole spectrum of minerals, not just sodium.