麻豆传媒

Increased sodium intake was not associated with higher risk of mortality over the course of 10 years in Medicare patients, , of Emory University, and colleagues reported in .

"There's been a lot of controversy recently about the appropriate dietary sodium intake," , of the University of Michigan, said in an interview. "Low sodium content in the diet might increase the levels of aldosterone and catecholamines and other so-called neurohormones that might contribute to cardiovascular damage."

Hummel noted that seniors who don't consume enough calories in general might not be consuming enough sodium. "The authors in this study did something that some other studies have not: they tried to adjust the sodium intake for the reported calorie intake of the participants also," Hummel said. "They really had similar conclusions. If you looked at the so-called sodium density of the diet ... there was still not really a clear relationship with cardiovascular events or overall mortality."

Hummel said that because the study population was considered healthy, this group might not be representative of other patient populations who might have higher cardiovascular risks associated with high sodium intake.

The Study

From 1997-1998, a group of 2,642 healthy participants, ages 71-79, who were still living in their community, were enrolled in the Health ABC study. The follow-up period spanned 10 years. Among participants, 51% were female, 38% were black, and 62% were white. No other races or ethnicities were represented.

At the 2-year visit, participants were asked to complete a 108-item food frequency questionnaire (FFQ). Sodium intake was categorized into three groupings: <1,500, 1,500-2,300, and >2,300 mg/d. At baseline, men reported higher median levels of sodium intake compared to women (2,850 mg/d versus 2,320 mg/d, P<0.001).

Adjustments were made for age, sex, race, baseline hypertensive status, BMI, smoking status, physical activity, cardiovascular disease status, pulmonary disease, diabetes, depression, heart rate, EKG abnormalities, and levels of glucose, albumin, creatinine, and cholesterol.

The authors noted that whites, as well as subjects who had diabetes, tended to consume higher levels of sodium. By contrast -- and not surprisingly given current recommendations -- participants with hypertension tended to consume less salt.

At the 10 year mark, 881 of the participants had died. Stratified by level of sodium intake, mortality rates were lowest in the middle group at 31%, compared with 34% in the low-sodium group, and 35% in the high-sodium group, but the differences did not reach significance (P=0.07).

The authors attributed this phenomenon to higher mortality risk in women, blacks, and participants without hypertension.

Kalogeropoulos et al, reported that sodium intake was not associated with an increased risk for death (hazard ratio (HR) per 1 g, 1.03, 95% CI 0.98-1.09, P=0.27).

Cardiovascular disease developed in 572 participants, and 398 developed heart failure.

When the researchers adjusted for calorie intake, they reported a 20% increase in mortality when measured per milligram of sodium per kilocalorie (HR 1.20, 95% CI, 0.93-1.54, P=0.47), but they found only an 11% increase in mortality risk when calculated per 100 mg/kg/m² for daily sodium intake (HR 1.11, 95% CI 0.96-1.28, P=0.17).

In a subgroup analysis, the researchers adjusted the model for competing risks for death and found that sodium intake only increased risk for cardiovascular disease by 3% (subHR per 1g, 1.03, 95% CI 0.95-1.11, P=0.47). The same analysis revealed zero affect on risk for heart failure (subHR per 1g, 1.00, 95% CI 0.92-1.08, P=0.92).

Analysis suggested sodium intake greater than 2,300 mg/d was not associated with increased mortality risk compared with daily sodium intake of 1,500-2,300 mg/d (HR 1.03 versus 1.15, 95% CI, 0.99-1.35, P=0.07).

When the researchers factored caloric intake and BMI into sodium intake, they reported that they didn't see much of an affect in the results.

The authors noted that the potential harm observed in patients who consumed more than 2,300 mg/d of sodium could be driven by the female and black participants.

Several limitations were reported in the study. Mainly, the FFQ created room for recall bias; participants were included on a voluntary basis; the study time-frame allowed for regression dilution; and there's a potential for unobserved confounding variables.

In terms of daily practice, this study provides little reason to implement widespread changes in clinical practice.

The 2010 U.S. Dietary Guidelines for Americans recommend adults consume 2,300 mg/d of sodium or less, and then to drop that number to 1,500 m/d for all adults over 50, and African Americans over the age of 2.

Previous research has suggested that reductions in sodium intake are unlikely to produce cardiovascular benefit.

However, a retrospective analysis of 13 randomized controlled trials that measured sodium intake with urinalysis found salt reduction reduced hypertension in both type 1 and type 2 diabetics.

Experts Weigh In

"The essence of the study says that the sweet spot is still in that 2,000-2,300 mg slot, which is what we've been doing for years," , of Mercy Medical Center in Baltimore, said in an interview. "I also question somewhat that the study suggests there's no racial difference. In practice many people have found that certain racial groups, specifically African Americans, may be more sensitive to the effects of salt, where others, Asian Americans perhaps, are not as sensitive."

In an interview with 麻豆传媒, , of the Cleveland Clinic, said the limitations of the study should be considered: "There's a very poor correlation between FFQs and actually measuring objective things such as salt excretion through the kidney, so, in general, people tend to underestimate their consumption of salt."

Krasuski said that although the study was well-powered, he agreed with Hummel that the patient population contained selection bias and did not reflect the general population. "This is data that in fact has limited applicability to the general patient that we see in our cardiovascular clinics," he said.

"We have to be careful how we discuss this particular type of study with our patients," Krasuski added. "Patients really want to know 'what should I be eating, what shouldn't I be eating,' and I think you have to be careful in saying 'well, salt isn't important because in this particular study, this is what they found.'"

"We know that higher levels of salt intake are bad for you," Krasuski said, referring to sodium consumption greater than 4 grams per day, although he also noted that the data are "all over the place."

He asserted that doctors don't want their patients leaving the office thinking that salt intake has not impact on health. Krasuski said that data and conclusions from studies like the one by Kalogeropoulos and colleagues aren't necessarily helpful in informing physicians on how to treat patients and make dietary recommendations.

“Nothing about this study (yet) changes practice today,” , of Northwestern University, wrote to 麻豆传媒 in an email. “It remains appropriate to advise sodium restriction as a means to prevent and treat heart disease, especially hypertension.”

Yancy agreed with Krasuski that the sodium cutoffs weren’t representative of the at-risk population’s actual diet. He also said that adjusting for all confounders can’t be done, so the data must be interpreted with caution.

Yancy, a proponent of the DASH diet, said blanket limitations for patients can be a blunt instrument, as salt restriction is only one component of a heart-healthy diet. “Our concerns today are not determining the incremental benefit of 1,500 mg/d versus 2,300 mg/d, but reducing dietary intake from 8-10 g per day … Remember, 60% of all sodium intake is built into the manufacture of food so even getting to 4 g/d is a challenge.”

“We are truly uncertain if aggressive sodium restriction during an acute episode is the best idea, but for the ambulatory patient with class III or more symptoms, we again have every reason to continue to recommend moderate sodium restriction,” he said.

Yancy’s recommendations for conversations with patients included focusing on three modifiable sources of sodium:

• Don’t add salt either at the table or in food preparation at home
• Be aware of the hidden sources of sodium, especially bread and soup
• Be especially careful with meals away from home, especially the “fast-food” or convenient meals

“These are all areas where a volitional decision can impact sodium intake. And finally, read the labels but read them correctly -- a banner that reads ‘lower sodium’ may be correct but the amount of sodium is still high; look for the FDA label and do the arithmetic," Yancy said.

From the American Heart Association:

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