Yes, salt raises blood pressure ...slightly.

Many studies report what seem relatively modest effects, but a few caution of risks of too much salt in the diet.

Revised 03-26-23 (added link to Kendrick articles)

Some weeks ago at a routine office visit my GP seemed quite accepting of my “I don’t trust health care anymore” speech and the news that I’d discontinued earlier meds, since they didn’t seem to offer much in the way of protective benefit. Her advice at end of visit? Watch my salt consumption, especially with canned foods. I’ve started doing so but only to a certain extent; I am not slavishly anti-sodium. Just the same, I am only an infrequent eater of canned goods. I do check labels, but I’m now more concerned about junk carbs (sugar, corn syrup, and the like). I just did an informal survey of my pantry, and yes, several cans of varying types of food seem to include substantial sodium. So no doubt, if your diet consisted mostly of canned goods, you would be likely they get too much salt. It’s worth noting, of course, that one can find canned goods that have less or even no added sugar or salt, but they do seem to be very much the exception rather than the rule.

Kendrick’s Wisdom

Dr. Malcolm Kendrick, my current health guru (or at least, I’ve lately read all four of his books) says basically that serious health risks are more likely from too low sodium (salt) than excess. His advice, rather than to cut sodium, is to increase potassium. This can be done by choosing certain foods, or the lazy man’s method (that’s me), by using potassium “salt” (I have two brands: Low-Salt and Nu Salt). I use these in place of normal salt when I cook or season my food.

Cochrane & My Earlier Delving

I don’t dispute that salt may raise blood pressure, but I’m curious, by how much? Just how big a factor is it?

This selection of Cochrane reports seems consistent with what Kendrick says in his book(s):

Minerals Calcium, Magnesium, and Potassium made little difference in blood pressures.

Various diets to lower sodium intake result in what seem to me to be quite modest BP reductions, 1 to 4 points at most.

Editorial [in Cochrane, I assume] claims that average reduction in BP is on par with many BP medications and significant. (When I was on the BP med lisinopril, my BP was reduced from about 134/82 to 123/75, a reduction of -11/-7 which is significantly more than the figures given by some of the salt studies I cite below. Granted, mine is a sample size of one.)

Cochrane Answers:

In adults, what are the effects on cardiovascular health of replacing salt with low‐sodium salt substitutes (LSSS)?

Tort et al (Aug. 2022):

Clinical Answer:

In adults (with or without hypertension), moderate‐certainty evidence shows that replacing salt with LSSS likely reduces non‐fatal acute coronary syndrome (358 vs 512 per 100,000 people; all results on average). Rates of non‐fatal stroke (178 vs 198 per 100,000 people) and cardiovascular mortality (605 vs 785 per 100,000 people) trended lower with LSSS, but did not meet statistical significance.

[Note that a duration isn’t given for those figures; that seems to be a common omission in these clinical reports. This is rather important. For example, the all-ages death rate (US) is about 900 per 100,000 per year. Cardiovascular disease is the top killer, but 785/900 = 87% of the total? I don’t think so. I cannot be sure, but it’s likely Cochrane’s time periods are greater than one year.] 

Moderate‐certainty evidence shows that replacing salt with LSSS probably lowers systolic blood pressure (SBP; mean difference ‐4.76 mmHg) and diastolic blood pressure (DBP; ‐2.43 mmHg). Very low‐certainty evidence suggests more controlled blood pressure with LSSS, but low‐certainty evidence suggests little to no difference in those meeting hypertension criteria (defined as SBP > 140 mmHg or DBP > 85 mmHg or the use of blood‐pressure‐lowering therapy in the last two weeks).

Moderate‐certainty evidence shows that although blood potassium is likely slightly higher (by 0.12 mmol/L) among people taking LSSS, there was no increase in the risk of hyperkalemia (defined as potassium > 5.5 mmol/L.

My notes: I did not find all-cause mortality studied. They did report cardio and stroke mortality. There were very small reductions with intervention, but it was not statistically significant. I did not find or calculate relative or absolute rates as I could not find a time period.

Midgely et al (1996) meta-analysis

https://pubmed.ncbi.nlm.nih.gov/8622251/

found "Dietary sodium restriction for older hypertensive individuals might be considered, but the evidence in the normotensive population does not support current recommendations for universal dietary sodium restriction."

S. Ebrahim et al (1998): meta-analysis of several factors,

https://pubmed.ncbi.nlm.nih.gov/9923952/

found that salt reduction lowered systolic BP by -2.9 in hypertensives, -1.3 in normotensive. This is similar to a prior study. (These are very small reductions, IMO).

Alam, Johnson (1999, meta-analysis)

https://pubmed.ncbi.nlm.nih.gov/10408586/

examined studies with patients 60 or older and found that chronic high NaCl diet significantly increased mean SBP and DBP by 5.58 mm Hg and 3.5 mm Hg respectively. Curiously (to me), salt intake affected SBP much more than DBP. Slightly different SBP/DBP hikes were reported: For trials with >= 60 years only, the figure was +5.46/+2.63; for subjects whose average age was close to 60, the figure was lower, +3.27/+2.69. These figures are consistent with what the above cited trials reported.

Rule of thumb I'm seeing: The older the patient, the more sensitive to high salt. But, IMO, the increases in BP seem relatively trivial, worst case (rounded up) = +6/+4. Normal BP varies far more than that even on a minute-to-minute basis. Why is salt painted the boogey man?

PubMed has many more studies (I searched “salt hypertension”); the above were just a few from the start of the listing of several hundred results.

Studies Supporting Stronger Correlations

Some studies claim a strong correlation between salt intake and increased risk of CVD. Here are a few.

https://pubmed.ncbi.nlm.nih.gov/19934192/

Strazzulo et al meta-analysis: “High salt intake is associated with significantly increased risk of stroke [23%] and total cardiovascular disease [14%; “Pooled estimate”  17%]. Because of imprecision in measurement of salt intake, these effect sizes are likely to be underestimated. These results support the role of a substantial population reduction in salt intake for the prevention of cardiovascular disease.”

Provisional Conclusion

The elderly and those with hypertension might wish to reduce salt intake, but even then, reduction in BP is likely to be modest, at most -6 systolic, -4 diastolic. Younger and normotensive patients will have lower benefit. In sum at least as long as I’m reasonably healthy, I don’t plan to obsess over salt. I will seek moderation and continue to use the Potassium salt when I cook.

More recently, I’ve found some studies that seem to support the claims that excessive salt may be harmful. I hope to look at more studies and see if I can clarify the apparent discrepancies.

Further Reading

Kendrick’s web site has several articles on salt. I’m still reading through them; by and large, it supports my own “investigation” above.Here’s a URL that will do the search for you:

https://drmalcolmkendrick.org/?s=salt