Nutritional Pearls: Beyond Blood Pressure
Richard, a 52-year-old man in good health, visits your office for his yearly physical. During the examination, he asks you, “I recently read that the amount of salt I eat really matter. Could it actually affect my blood pressure? What about other illnesses?”
How do you answer your patient?
What is the correct answer?
(Answer and discussion on next page)
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Answer: The preponderance of evidence lands on the side of keeping patients’ sodium intake within the Institute of Medicine's recommended limits, even if they do not have diagnosed high blood pressure
I was giving a talk to the public last week and a member of the audience said that his doctor told him that “salt didn’t matter” and not to worry because it doesn’t have much effect on blood pressure.1
Interestingly, I was able to note that researchers at the University of Delaware wrote a very useful review article to summarize the state of the research on dietary sodium and blood pressure. Here are some highlights of their conclusions:
Sodium Intake Levels Not Ideal in Many Elderly Patients
5000 mg of Daily Sodium OK for Heart
Those patients whose blood pressure decreases when they reduce the amount of sodium in their diet (or increases with more sodium) are considered "Salt Sensitive," while those whose blood pressure does not change are known as "Salt Resistant." Those people with normal blood pressures who can be identified as Salt Sensitive appear to be more likely to develop high blood pressure later and have a higher risk of all-cause mortality, but the total number of people whose reactions are clinically significant are very small.
Why Sodium Increases Blood Pressure
Research to understand just how sodium causes blood pressure to change is ongoing, but recent research shows that it includes kidney function; hormones that control the body's fluid balance; the heart, veins, and the heart's output; and genetic mechanisms.
Effects of Sodium on Organs
Very interesting research suggests that high levels of salt in the diet can still negatively impact various organs even in the absence of high blood pressure.
Arteries: Higher levels of dietary sodium actually stiffens the arteries, which impairs their ability to dilate or constrict, and damages the endothelium.
Heart: High sodium intake can thicken the wall of the left ventricle of the heart, which is responsible for pumping blood to the rest of the body (the right ventricle pumps blood to the lungs).
Brain: Research in rats suggests that high salt in the diet makes brainstem nuclei react more strongly to various stimuli, leading to a greater variation in blood pressures even though the average blood pressure may not increase.
Salt Intake and Blood Pressure
The authors acknowledge that the ideal would be to perform a long-term, randomized controlled trial comparing different levels of salt in the diet. That's not really feasible, however - imagine trying to get thousands of people to stick to exact amounts of salt intake in their diet for multiple (dozens, perhaps) years. Meta-analyses of smaller studies as well as systematic reviews show "a strong positive association" between sodium intake and systolic BP.
Cardiovascular Disease and Illness or Death
Most of the research that analyzes the association between dietary sodium and cardiovascular disease are observational studies, which of course cannot show causality. It's also very difficult to measure dietary sodium intake very accurately over the long term (the gold standard is urinary excretion), and many studies are short-lived for that reason. That said, the research looking at the opposite—that very low sodium is associated with heart disease, illness, or death—is unclear and mostly speculative.
What’s the Take-Home?
You can advise your patients that the preponderance of evidence lands on the side of keeping their sodium intake within the Institute of Medicine's recommended limits, even if they do not have diagnosed high blood pressure. Here’s a guide for your patients to 3 easy steps to reducing the sodium in their diet: http://www.drgourmet.com/specialdiets/lowsodium/3steps.shtml
1. Farquhar WB, Edwards DG, Jurkovitz CT, Weintraub WS. Dietary sodium and health: more than just blood pressure. JACC 2015;65(10):1042-50