I have always been strangely suspicious of the highly publicized assertion that eating salt is a cause cardiovascular disease (CVD). Maybe as a chemistry student, I disliked seeing this vital electrolyte and perfect cuboid crystal receive continuous bad press. Or maybe its because for some inexplicable reason at school we had a whole double period based entirely around the Salt Manufacturers Association website.
Whatever the reason, according to a new meta-analysis, the Salt Manufacturers of GB (and my innocent brainwashed mind) may not be so wrong. As reported at Nature.com, the meta-analysis (a study of studies), published in the American Journal of Hypertension, has concluded that there was no significant benefit to reducing salt intake. Now, to be fair, this is one of literally thousands of studies on the relationship between salt and CVD, many which have found the opposite result. For example, as is mentioned in the Nature article, another meta-analysis from 2009 found that a high sodium diet increased risk of stroke by up to 23%. So what does this mean – is salt a problem or isn’t it?
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| Sodium chloride is the major salt in our bodies and food Rob Lavinsky |
The reality, is that the answer to the salt question remains unknown. Physiologically, it makes sense that continuous high salt intake could lead to increased blood pressure - if our kidneys have to retain extra water to maintain the correct salt concentration in our blood. But in actual fact our kidneys are very good at getting rid of salt we don’t need in our urine, and so are able to keep salt levels well in check, as long as we don’t literally drink brine.
The problem with studies examining the link between salt and cardiovascular diseases is that it incredibly hard to measure salt intake accurately over an extended period of time. And it is even harder to control for other factors which have a proven influence in cardiovascular disease, namely the intake of sugars and fats, exertion and smoking rate. More often than not, measuring salt can just act as a substitute for measuring calorific intake. Thus results between different studies vary widely, and we are left not really knowing if excess salt is harmful or not.
What we do know is that Japanese people eat more salt than British people, but have lower rates of CVD related death. In the 1996-99 INTERMAP Study, daily salt intake was estimated to be around 210 mMol (around 12g) for Japanese men, compared to around 170 mMol (around 10g) for UK men. The WHO recommended daily limit is 5g. And yet 24.7% of Japanese men die of CVD, compared with 37.6% of UK men. Like all statistics these should of course be treated with, my apologies, a pinch of salt (as pointed out on the Radio 4’s More or Less, fewer people France die of CVD then in the UK simply because in the UK unexplained deaths are more often attributed to CVD). However there is a strong suggestion here that salt cannot be a major contributing factor to CVD risk.
I am not advocating a mass increase in salt intake. It is quite probable that there is some link between salt and CVD, especially with for those with exceptionally high salt intakes or those who are already at risk of CVD events. However for most people on a normal western diet this link is unclear or marginal. The link between intake of saturated fat and CVD is not. Obese people get strokes, heart attacks, and diabetes at a much higher rate then normal weight people do. WHO estimates that 2.8 million people die every year as a direct consequence of being obese. Not only this, but obesity is extremely impactful on a person’s quality of life and on a healthcare system's budget. I can’t help but feel that all the efforts by the government and industry to reduce “hidden salt” could be better-spent promoting low calorie lifestyles and subsidising fruit and vegetables.
Of course, the more pressing problem is the way foods are marked and marketed, and how the issue of salt is communicated to the public. Eating salt and overeating are often presented as equivalent sins, when it is clear this is not the case. How easy is it to equate one of the little green segments of the wheel of health smugness on Sainsbury’s packaging for another? The selection of a high fat, but low salt product is marketed as a health compromise.
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| Green cancels Red? |
Only 29.8% of Japanese males over the age of 15 are overweight or obese (BMI of >25) whereas a truly shocking 67.8% of UK males meet the qualification. It seems clear to me that body fat is a dominant effect, whereas salt intake should only ever be a secondary consideration. Heath guidance to the public needs to be clear and unambiguous, and presenting salt intake as an equal evil to fat and refined sugar intake, will inevitably effect peoples’ eating choices. Research into the effects of salt and CVD should and obviously will continue - however the current message that reducing salt is as important as reducing fat is misleading, and gives people an easier healthy alterative. Having no salt on your daily chips will not stop you getting cardiovascular disease. Not having your daily chips may just do.
