Study Suggests Salt Restriction Only Beneficial In People With Hypertension

–More questions raised about broad efforts to restrict salt; AHA condemns study

A large new analysis offers more evidence that broad salt restriction doesn’t benefit most people and may even harm some people. The study did find that salt restriction may be beneficial to the minority of people with high blood pressure who also consume high levels of salt. Though by no means a definitive study, the paper published online in the Lancet adds to growing concerns that population-wide efforts to restrict salt may be misguided. However, the American Heart Association said “the public should not be confused by the flawed study” and said it stands by its support for low-salt diets.

Average sodium consumption in the United States is 3,400 mg per day. The American Heart Association recommends that sodium levels be no higher than 1,500 mg/day, while some other organizations recommend sodium levels below 2,300 mg.

The new analysis combines data from more than 133,000 hypertensive and normotensive people who participated in four large prospective studies. Salt consumption was estimated by measuring sodium from a urine sample. For both hypertensive and normotensive people low levels of salt consumption below 3,000 mg per day were associated with an increased risk of cardiovascular disease and death. However, at the highest levels of salt consumption (more than 7,000 mg per day) there was an increased risk in the people with hypertension but no increased risk in people without hypertension.

“While our data highlights the importance of reducing high salt intake in people with hypertension, it does not support reducing salt intake to low levels,” said the lead author of the study, Andrew Mente, (McMaster University), in a McMaster press release. “Our findings are important because they show that lowering sodium is best targeted at those with hypertension who also consume high sodium diets.”

The authors recommend that population-wide efforts to lower salt consumption should only be undertaken in areas like central Asia or China where the average sodium intake is very high.

The Debate Goes On

Speaking on behalf of the American Heart Association, Elliott Antman (Brigham & Women’s Hospital), said he strongly disagreed with the methods of the study along with its conclusions:

“It is disappointing to see that a flawed methodological approach to the important question of the relationship between sodium intake and cardiovascular events is perpetuated in this latest publication. Use of spot urine specimens obtained first in the morning are not a good surrogate for the gold standard, which is serial 24 hour urine measurements. Thus from the very start there is an unreliable estimation of the 24 hour urinary sodium at baseline — that is, at entry into the studies that are pooled in this report. Furthermore, it is unrealistic to expect that a measurement of urinary sodium at entry into the studies that are pooled can provide a reliable estimate of the sodium intake during the course of followup of the studies. Thus we cannot have confidence in the relationships between sodium and outcomes that are reported in this paper. We cannot use the information in this paper to guide public policy. The AHA maintains its previous statements of the concerns about the approach taken in such analyses and continues to recommend less than 1500 mg of sodium per day for all sources.”

Andrew Mente and another study author, Martin O’Donnell, offered the following response to Antman:

“In developing public policy, large population studies are required to describe the relationship between sodium (salt) intake and health outcomes in the general population. While repeated 24-hour urine collections may be the reference standard for measuring sodium intake in individuals or small groups, they are completely impractical and arguably unnecessary for large population studies. Use of a fasting morning urine to estimate sodium intake in populations has been shown to provide reliable estimates (compared to 24-hour urines), and accepted by leading medical journals (Lancet, NEJM, JAMA) and the WHO as a practical approach to measuring intake in populations. The generalisability of studies using fasting urines is superior to 24-hour urine collection, as the latter is associated with high rates of non-completion. Use of a single measurement of a risk factor in populations is common in medical research. Major advances in our understanding of the importance of blood pressure, diabetes and cholesterol have been based on single measurements of these risk factors in large epidemiologic studies (e.g. Framingham, INTERHEART)-consider the consequences of ignoring those studies!

A recommendation for low sodium intake (<1.5g/day) in the entire population should be based on definitive proof of benefit, rather than merely attempting to disprove studies that contradict. We are unaware of any studies demonstrating that sodium intake of <1.5g/day is significantly associated with lowest cardiovascular rates in the general population (compared to moderate), but are aware of numerous studies (including those using 24-hour urine collections) that report a higher risk in those with low sodium intake. A meta-analyses of these previous studies report moderate sodium intake to be associated with lowest cardiovascular risk, even when studies using ‘spot’ urine measurements are excluded. The current recommendation for low sodium intake is based on an assumed cardiovascular benefit, inferred from small blood pressure trials. Current evidence, from international studies conducted over the past 6 years, suggest that those assumptions may be flawed, and guidelines need to be updated to reflect contemporary evidence.”

See also: The American Heart Association’s Strong Stance Against Science

Previous Coverage of the Salt Debate:

 

Comments

  1. To trust or not to trust in medical science

    This is another example of research for convenience, which is confusing and contradictory to the previous study conclusions. I am forced to analyze and critic this Canadian study published in the British journal as a non-scientist who personally took care of 53,000 patients in the last 40 years in a small town in USA. Most of my patients had been cared for their diabetes, hypertension and cholesterol problems and I had the opportunity following their problems and complications for many decades without any inclusion or exclusion criteria. On this issue of salt restriction, I do agree with AHA who condemns and disagrees with the conduct and conclusions of this new analysis/research. My opinions will be marginalized as anecdotal and not science, as the 53,000 subjects were not enrolled scientifically in the database and analyzed with multiple statistical methods in different ways to get the expected conclusions.

    The pooled analysis of the data from four studies showed the association of urinary sodium excretion, and not salt intake of the patients in the 4.2 years of study with non-adjudicated cardiovascular events and mortality. With so many assumptions and deductions from previous studies of the researchers’ choice, the data suggested, not confirmed, that low sodium diet, not few urinary spot readings in few years, is best targeted at populations, not individual patients, with hypertension who consume high sodium diets.

    My patients’ salt intake varies every day depending on whether they eat home cooked food, ethnic food, restaurant food, fast food, snack food etc. Spot urine or 24 hour urine sodium on a particular day entered in the database doesn’t in any way tell the patient’s sodium intake for months and years. Large population study centers with highly sophisticated computers and PhD researchers are good research mills to crank out research papers for publications on both sides of the Atlantic Ocean. Reliable data collection may be completely impractical doesn’t make it unnecessary, to get reliable conclusions for the average patient on the street to benefit from.
    It should not be a case of garbage in and garbage out, no matter who want to cash in on it whether they are from the south or north of the border.

    The salt is bad or not bad argument is going on for decades so much so that patients and their doctors are sick of hearing the arguments and trust nobody and resent the fact that so much money is wasted on the so called self-serving research industry. Studies come and go in cycles and patients won’t get much help, should not be the end result. Reliable estimates accepted by leading medical journals doesn’t cut it as we have seen so many corrections and retractions after many years of the original publication of clinical trials with the recent entry of even a Retraction Journal itself in the field. This paper is another example of the “Street light effect” and “Matthew effect”. The public and the physicians have become so critique and skeptic and lost their faith in the medical research. What comes in the scientific journal doesn’t make it scientific or biblical because Bible doesn’t have corrections, retractions or new editions.

    Meta-analysis of previous studies are the new wave of research coming out recently with the introduction of sophisticated digital technology and the abundance of post-doctoral graduates who never saw a patient, with contradictory and confusing results on the same issue, spinning theirs as the last word on it to be proved wrong later by another group. I am reminded of a comment by an experienced expert: Clinicians should be wary of changing their clinical practice based on a meta-analysis. He added, “It’s not research, it’s sitting at a computer, dredging through data.” The conclusions are affected by the choice and interpretation of the results and manipulation of statistical analyses.

    Salt sensitivity appears to be genetic and differs in different ethnic groups causing or aggravating hypertension. Caucasians are least affected by high sodium diet. Asians, Chinese, Orientals, Blacks and Latinos are the major groups susceptible to adverse effects of high sodium diet. It may be completely impractical to sort out these population groups in this world with so much diversification, to do studies to get reliable results. Low sodium diet should be recommended for cardiovascular benefits for population at large as we have no way of early predicting who will develop hypertension or heart failure without waiting for their occurrence and then act on it after it happens.

    Over the last five decades we have evolved in understanding different facets of hypertension- systolic, diastolic, labile, white-coat, masked, nocturnal, variability and so on and diagnostic numbers have changed from 160 to 120 in systolic B.P. to be called hypertension.
    Similarly, the diagnostic criteria for diabetes have changed from a fasting glucose level of 140 to126 and 100 to 125 for prediabetes. As for the total cholesterol the number got changed from 360 to 300 to 240 and 200 to diagnose hypercholesterolemia.

    Current evidence from international studies over the past 6 years are flawed and we need to accept the contemporary evidence to update the new guidelines du jour. Over the last 40 years, this author has tasted so many “research soups du jour” and didn’t have the full faith to swallow them. Stay tuned for the next contemporary evidence for the Customized Common sense Care of your patients.

  2. nice information.

  3. Melissa Mellie says:

    Thanks for sharing this information. If you have high blood pressure problem then you should reduce the quantity of salt in your diet and also take medicine regularly.

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