There is a workaround to restricting the salt content in people’s diet, says S.Ananthanarayanan.
“If the salt have lost its savour, wherewith shall it be salted?” asks the apostle, Mathew, in the Bible. But it is this savour that may be the undoing of salt, for salt in human diet is notorious for pushing up blood pressure. A group of researchers in Boston University, however, think there is a way to salt our food and keep our cool, too
Jesse D. Moreira, Parul Chaudhary, Alissa A. Frame, Franco Puleo, Kayla M. Nist, Eric A. Abkin, Tara L. Moore, Jonique C. George, Richard D.Wainford describe, in the journal, Experimental Physiology, their work on the mechanism by which salt has this effect on the body. They note that there is a fortunate section of people which is ‘resistant’ to the rise of BP despite a high-salt diet, and they suggest a way for all of us to follow suit.
Elevated blood pressure, or hypertension, which the WHO report of 2013 calls a ‘silent killer, global public health crisis’, affects over a billion people, or one in every three adults.” It contributes to the burden of heart disease, stroke and kidney failure and premature mortality and disability,” the report says, and that hypertension is responsible for nine million deaths each year.
One of the reasons for blood pressure to rise is the increase in the volume of blood in the body. Kidney malfunction, which leads to less extraction of water from the bloodstream, could be a reason. But a more frequent reason is higher salt content in the bloodstream, which leads to processes that retard the kidneys and block the extraction of water. The heightened blood pressure that results also helps to promote excretion of the higher salt content of the blood
The way this reaction to high salt content comes about is by the action of a part of the brain called the hypothalamus. This almond-sized organ, just above the brain stem, is responsible for a number of automatic responses of the body. One of these is to sense the salt content in the blood. When the hypothalamus senses high levels of salt, it stimulates secretion of a hormone that slows down the action of the kidneys. The high salt level in the bloodstream also draws water out from body cells. The body then feels thirsty and drinks water. All this dilutes the blood, but the volume of the bloodstream increases.
Another, important action of the hypothalamus is turn on the emergency system of the body in the face of danger or different kinds of stress. This includes hormones that increase the heart rate and constrict the blood vessels. These effects are also seen to chip in when the stress is a high salt content in the blood.
While there are several reasons for a person to be hypertensive, by far the most prevalent is high salt intake. The diet of primitive humans was largely meat from animals that they hunted, and the meat was eaten raw within hours of the animal being killed. There was almost no salt intake and there is evidence that rising blood pressure was non-existent. It is when agriculture was developed that salt intake grew, with rising incidence of hypertension. Lewis Dahl, who demonstrated the strong Iink of high salt intake with hypertension in the 1960s, records that the diet of people living in northern Japan included about 30 g salt in a day and there was almost 40% prevalence of hypertension. Whereas Alaskan natives consumed less than 5 g of salt in a day and the prevalence of hypertension was almost zero. Initiatives taken in Japan in recent decades have reduced salt intake nation-wide and Japan now has one of the lowest incidence of hypertension.
Dahl also found that of a population of rats fed a high salt diet, three-fourths became hypertensive, but not the remainder. There was hence a genetic element and Dahl was able to breed salt-sensitive and salt-resistant strains. Among humans also, while blood pressure tends to rise or fall with salt content in the diet, a condition called salt-sensitivity, there is the salt-resistant group, which is able to get rid of the salt efficiently, and see no rise in blood pressure with a high salt diet.
The group working in Boston note that while the central mechanisms that lead to salt sensitivity have still not been understood, it could be promising to study the factors at play in ‘salt-resistance’. The group hence carried out trials on a group of experimental mice that had been fitted with a device to wirelessly transmit the blood pressure in the arteries of the animal to observers.
The group refer to previous research which suggests the role of a specific protein that acts to suppress the body reaction to high salt levels in salt-resistant mice. The protein, and a substance that suppresses the response to the protein were hence administered to the experimental mice over a period of seven days and the behavior of the blood pressure, and other parameters, was observed. The paper reports that role of the protein in preventing inflammation in the part of the hypothalamus that is associated with salt-sensitivity has been made out.
“Our findings have implications for the development of personalized anti-hypertensive therapeutics designed to target the pathway involved in changing cells to bring about salt-resistance in the body,” one of the authors of the study is reported to say, in a press release
The current approach to managing hypertension is with the use of agents that promote kidney action and urine production or by suppressing the production of hormones that push up the blood pressure as a reaction to stress. The effective way of diet control does not appear to be immediately practicable, one reason being the use of salt as a preservative. Medication has proved useful in the developed world, but uncontrolled hypertension remains a scourge in many countries. Extending the capacity not to become hypertensive even with a salt-rich diet represents a new approach that may eliminate the disease at its root
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