ageing, disease, food

Salt, Cardiovascular Disease, and Death: Controversial Correlations

Just last Thursday, three papers were published in The New England Journal of Medicine that came to very different conclusions about how much table salt (sodium chloride) we should have in our diets if we want to avoid cardiovascular disease and a related death. While two of the studies suggested that most people could safely eat more salt, the third study reported that high numbers of cardiovascular disease-related deaths — specifically 1.65 million in 2010 — are due to eating lower levels of salt than this. It’s clearly a controversial topic that draws a lot of interest because it potentially affects so many people.

pretzels salted salty hand
Is it time to reconsider eating that extra handful of salty pretzels? (Image credit: Project Manhattan)

First we’ll explore the papers that might make you less afraid of shaking a few dashes of salt onto your next meal. These two papers are a part of the large-scale PURE (Prospective Urban and Rural Epideimological) Study — they basically show that high levels of sodium may not necessarily be harmful unless you are in a certain high-risk group, and that the relationship between eating salt and increasing blood pressure levels is not linear.

One of the PURE papers used urine samples from 102,216 adults (from 18 different countries) and analyzed the levels of salt in their urine. It was found that when people had significantly higher amounts of salt in their urine (presumably due to a high-salt diet), had hypertension, or were older (greater than 55 years old), their blood pressure increased steeply with increased salt levels. (But for people who had lower salt levels, didn’t have hypertension, and were less than 45 years old, there was not a steep increase in blood pressure.) This reveals that the relationship between salt levels and blood pressure is not a linear one. (For the curious — there was a typical increase of 2.11 mm Hd in systolic and 0.78 mm Hg in diastolic blood pressure for every 1.0 gram increase of salt in a person’s urine.)

The second PURE paper similarly used urine samples from 101,945 people in 17 countries, but this time they looked for correlations between salt levels, cardiovascular disease, and death. They found a lower risk of death and cardiovascular disease for people who consumed 3 to 6 grams of salt each day (compared to people who ate more or less salt). (The average amount of salt a person consumed was 4.93 grams in a day.) The study did not find an increased risk of death and cardiovascular disease unless a person ate more than 7 grams of salt each day, and they again saw the strongest correlations for people with hypertension (with an increased risk becoming apparent with only more than 6 grams of salt consumed per day). However, an increased risk was also observed for people who ate too little salt, specifically less than 3 grams per day.

But don’t get too eager to grab those salty pretzels. As mentioned earlier, a third paper was published last Thursday that strongly cautioned against eating too much salt. Specifically, the third paper drew upon data from 205 surveys, using people from 66 countries, which the authors say accounts for “74.1% of adults throughout the world.” They found the average salt consumption to be 3.95 grams each day, and concluded that eating more than 2 grams of salt per day was responsible for 1.65 million deaths in 2010 (due to cardiovascular disease). (In an interview, it’s suggested by an author of the PURE papers that this number may be closer to less than 0.5 million deaths.)

For the record, the 2010 Dietary Guidelines for Americans recommend eating less than 2,300 mg [2.3 g] of salt per day.

So while it’s clearly still hotly-debated how much salt you should have in your next meal, like many things in life, moderation may be the best route.

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