Why salt is more complex than its users might think

• This white crystalline substance used for seasoning or preserving food is loved and loathed in almost equal measure. But how is this for a fact? 

To what lengths are you willing to go to keep your salt intake within acceptable standards? If you do not mind swapping your table salt with sea salt, it will set you back just under Shs200,000—a staggering amount by any measure, especially with the current inflationary pressures. And if you want to answer that decades-old 'how much is too much' question, suppressing the culinary godsend will come at the cost of your food tasting, feeling, looking, and even smelling better.

This white crystalline substance used for seasoning or preserving food is loved and loathed in almost equal measure. But how is this for a fact? The first-line treatment of high blood pressure or hypertension is, wait for it, significantly scaling back salt intake. Hypertension, per the World Health Organisation (WHO), "is when the pressure in your blood vessels is too high."

You are hypertensive, doctors say, when the force of blood pushing against your artery wall is consistently high. It sounds simple enough until you are walked through the mechanics of blood pressure readings—the systolic number, on the one hand, and the diastolic number, on the other hand. The former captures when your heart contracts and the latter when the same organ rests. If a measurement returns a systolic number of 120 or below over a diastolic number of 80 or below, the all-clear is given. Anything above, even if marginally, leaves one teetering on the edge of danger.

Non-communicable diseases

So, where—one would ask—does salt figure in the grand scheme of things? Listening to the latest episode of BBC World Service's The Food Chain podcast, I was at once struck by the simplicity of the explanation of Clare Collins, professor of nutrition and dietetics at the University of Newcastle in Australia. She used a metaphorical expression in a bid to get closer to the seemingly impenetrable heart of a disease that often goes undiagnosed. Salt was situated in a chain reaction that can, at first glance, be so fiendishly complex.

"So, when you have too much salt, the first thing your body says is: 'I'm gonna dilute you.' So, it retains water," she told The Food Chain, adding, "So, your blood pressure is going to have a bit of a [spike] to pump all this fluid around your body, and that's actually why your blood pressure goes up."

Onto the metaphor proper, Prof Collins says: "[…] think about your arteries like the same way you would your garden hose. If you get your hose out every day and you turn it on at a nice volume and you water all your plants, your hose is going to last forever and ever. But if every day you turn that hose on full bore, like a fire hydrant amount of water blasting through your garden hose, well that garden hose is not going to last very long. And so, essentially, that's what's happening in your arteries. And then if you have any weaknesses in those blood vessels, like in your brain, that could burst and you could have a stroke."

Back to that consequential question then: how much is too much? Well, the WHO recommends less than five grammes each day. This works to about just under a teaspoon. To be clear, despite the weight of numbers growing to the point that we have to halve our salt intake at the global level, sodium can be disarmingly wonderful. Its rockstar prestige in various kitchens owes to the fact that it teases out aromas to whatever lists it as an ingredient. Without it, bread wouldn't have that inviting brown hue that singles consummation. Ditto other foodstuffs either baked or fried. Heck, we are fated to die when our bodies run low on sodium. Why? Because salt helps cells function optimally. Along with neurones, the brain, skin, muscles and bones all—to a certain degree and in some form—need salt.

Delicate balancing act

In fact, such is the scientific ingenuity of this white crystalline substance that it remarkably suppresses bitterness in some foods. On The Food Chain last week, Paul Breslin—whose interest in human oral perception and its genetic basis is well documented—drew attention to how a sprinkle of salt on a grapefruit can accentuate its sweetness by knocking the bitter flavour down. A similar effect to taste receptors happens with the seemingly raw mangoes that sprout from Ugandan soils, affirming salt's reputation as, perhaps, the ultimate flavour disguiser.

But before you ask for the salt shaker at the dinner table, it would be unwise to be tone-deaf to the fact that salt bumps up the risk of dying prematurely. A 2016 study published in one of the American Academy of Neurology's journals found that "high urine sodium and high salt-diet preferences were more frequent among post-stroke hypertensive patients in Uganda than in their non-hypertensive counterparts." The case-control study carried out in Uganda involved 123 "post-stroke patients with a history of hypertension" and 112 "post-stroke patients without known hypertension."

The researchers from Makerere University concluded that there was "no difference in dietary salt knowledge between [post-stroke hypertensive patients in Uganda and their non-hypertensive counterparts]."

They added: "The development of educational strategies that include salt-diet preferences may lead to better blood pressure control in this high-risk population."

So, taming your salt habit might not be such a bad thing.