A recent NIH study suggested that aggressively lowering systolic blood pressure below current guidelines of 120 mg—by aggressively they meant giving more medications—could reduce deaths from cardiovascular disease.
Around the time the study came out I was in a hospital cafeteria getting something to eat when I noticed two ladies standing behind a table. On the table were trays full of sandwiches.
“What’s this for?” I asked.
“We’re with the nutrition department, trying to get people to try some low sodium options,” one of them said, “this is low sodium wheat and turkey, and this one is a low sodium pretzel bun—”
I don’t remember what she said after pretzel bun because I zoned out. I was astounded that pretzel buns were being offered as a food to reduce high blood pressure.
“With all do respect,” I said, “I think the pretzel buns are more problematic than the sodium.”
She seemed taken aback by my comment, but I doubt I said anything radical that day.
It’s great that they were addressing high blood pressure with a food based approach but to me it made no sense to offer low sodium options in the form of processed food.
Sugar, not sodium, has come to light recently as a major driver of high blood pressure. And processed foods usually contain added sugars like high fructose corn syrup, or are themselves sources of refined carbohydrates that rapidly break down into sugar.
Here on the BDN Michael Noonan, in his article “Sugar, not salt, eyed as the new culprit in heart disease,” linked to an article “The Wrong White Crystals” from the British Medical Journal, BMJ, outlining the links between sugar high blood pressure.
The authors make the point that sodium consumed in the western diet usually comes together with processed food, leading to the vilification of sodium when it’s really the simple carbohydrates that are to blame.
The article goes into detail about the direct and damaging effects of sugars that lead to high blood pressure. For example, fructose has been shown to stimulate the sympathetic nervous system, speeding up heart rate—the more blood pumped into the arteries per minute, the higher the blood pressure. It has also been shown to drive insulin resistance.
In the last year I have seen the media bring much attention on the link between sugar and high blood pressure without much discussion on the link between insulin resistance and high blood pressure. I think it’s worth mentioning.
Perhaps the link between insulin resistance and hypertension makes more sense from an evolutionary standpoint.
Early humans lived in a time of varying food availability. During times of food abundance they stored excess calories in adipose tissue and skeletal muscle under the direction of insulin. During times of food scarcity these tissues became mildly insulin resistant in order to release these energy sources for supply to vital organs like the heart and brain. In other words, mild insulin resistance prevented starvation.
Insulin resistance gets a bad rap, but it is a normal function during periods like fasting, illness, trauma, and pregnancy, all instances where energy sources need to be allocated towards vital organs or a developing fetus instead of selfishly stored in fat reserves.
Insulin played a role in the way our ancestors maintained their blood volume during scarcer times by acting on the kidney’s sodium retaining machinery. The body’s way of increasing blood volume is to save sodium. Sodium is charged so it pulls water with it.
During times of scarcity this functioned to provide enough blood for vital organs, especially the brain.
Inflammation and insulin resistance went together as the production of inflammatory molecules called cytokines made tissues less sensitive to insulin. This was advantageous for our ancestors, meant to last only a few weeks until a period of hunger or illness subsided.
We’re built to store calories for times of food scarcity, and to become less responsive to insulin when those hard times hit. The problem is that in today’s world a lot of us develop chronic insulin resistance and inflammation in the face of caloric overabundance, causing these normal survival mechanisms to persist and become harmful for the body.
Inflammation also causes tissues to become more porous. Think about an injury you might have had, like a cut. It was red, swollen and probably a bit leaky. Inflammation throughout the body causes systemic water loss, and to save water the body launches a more powerful mechanism to retain sodium. This cycle, in addition to insulin’s action on the kidney, increases blood pressure.
Normally, insulin is not inflammatory and actually dilates blood vessels to help sugar flow to insulin dependent tissues like fat. But higher than normal blood levels of insulin, hyperinsulinemia, becomes inflammatory to blood vessels, contributing to systemic water loss and sodium retention. Hyperinsulinemia also causes vascular constriction, further increasing blood pressure.
The link between insulin resistance and hypertension has been established for decades.
A Banting Lecture published in 1988 devoted a section to the link between insulin resistance and hypertension, stating:
“It now seems relatively clear that higher than normal plasma insulin concentrations are commonly found in patients with high blood pressure,” and that “some degree of glucose intolerance has been described in patients with high blood pressure.”
Even this news from 1988 isn’t old news. Go back half a century to 1938 when British medical researcher Harold Himsworth already posited that disordered insulin metabolism was at the root of many diseases, not just hypertension.
While there is a strong link between insulin resistance and high blood pressure, and convincing evidence from our evolutionary history to suggest impaired insulin signaling does play a role in its development, insulin resistance has not been confirmed as a definite cause of high blood pressure.
It’s possible that both hypertension and insulin resistance stem from the inflammation caused by a carbohydrate heavy diet.
So, are low sodium foods generally a good way to reduce high blood pressure?
Some people are more sensitive to salt than others, they’re “salt-sensitive,” so for them watching their salt intake could be helpful in reducing hypertension to some degree.
On the other hand, there are many “salt-resistant” people” who can’t lower their blood pressure with sodium restriction. This alone shows there’s a lot more to high blood pressure than sodium intake alone.
As the authors of the BMJ article wrote, “Maybe lowering sodium intake is a step some people should take, but it doesn’t make sense to offer low sodium options in the form of processed food.”
Indeed, this may only lead to an increase in the consumption of processed food, leading to more heart disease.