10 September 2012

Salt - Is it the Cause of Hypertension?

Today, it is a common assumption that excess salt consumption leads to high blood pressure, which is a risk factor for heart disease and stroke. Hypertension is very common in obese and diabetic patients.

"[...] The higher the blood pressure, the higher the cholesterol and triglyceride levels, the greater the body weight, and the greater the risk of diabetes and heart disease."
                                                                                - Gary Taubes
If diabetes, heart disease and hypertension have higher chances to occur in the same person, then the cause must be the same: sugar and refined carbohydrates.

Normally, when we eat salt (sodium), in order to maintain the sodium concentration constant in our bloodstream, we retain water (high sodium concentration in our body would be dangerous). When water retention is higher than normal, our kidneys will excrete salt into the urine along with the water. So everything works fine. This water retention, caused by salt consumption, results in a mild increase in blood pressure, which is not dangerous as long as our kidneys are able to eliminate the excess salt and water.

Technically speaking, hypertension is higher than 140/90 mm Hg. If hypertensive patients cut down on salt in their diet, it will only result in a decrease of a few mm Hg from the 140/90 mm Hg, which is not very impressive, and does not make a lot of difference. I think it's better to concentrate on what causes that 20 points of increase in our blood pressure, over the healthy levels of 120/80 points.

When we eat carbohydrates, we retain more salt, so our body's response to these high concentrations of salt, is more water retention, resulting in higher blood pressure. Carbohydrates inhibit the release of salt and water into the urine.
"With diets predominantly carbohydrate there is a strong tendency for the body to retain water, while with diets predominantly fat there is a tendency for the body to lose water."
                                                 - Francis Benedict (Carnegie Institute of Washington)
So, if we want to lose water, and so lower our blood pressure, it makes more sense to reduce our consumption of carbohydrates, rather than our consumption of salt.

Despite the lack of evidence in support of the salt-causing-heart-disease hypothesis (Jeremiah Stamler called this theory as "inconclusive and contradictory"), health authorities still recommend hypertensive patients to cut down on salt.

In native populations, hypertension did not exist. In fact, physicians observed the opposite of what was happening in the Western world: blood pressure tended to decrease slightly with age.
"The Kenyan nomads in their sixties had an average systolic blood pressure forty points lower than that of European men of the same age. [...] With exposure to Western lifestyle and diets, however, blood pressure among these native populations began to rise with age, as it does in Europe and America, and the average blood pressure and the incidence of high blood pressure increased as well."
                                                                     - Gary Taubes
So, Western diet (more carbohydrates and sugar) - and not salt consumption - is a contributor to hypertension.

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