IOM：应减少钠摄入但不宜低于每日2.3克

美国医学研究所(IOM)5月14日发布报告指出，美国人应减少钠摄入量以改善健康，但每日摄入量不宜低于2,300 mg。年龄≥51岁、非裔以及患有高血压、糖尿病或慢性肾病者也可遵循这一建议。

上述建议与美国健康与人类服务部(HHS)提出的美国人膳食指南并不一致，后者建议高危者应将每日钠摄入量限制在1,500 mg以下，而年龄介于14~50岁的其他人多数应将钠摄入量限制在2,300 mg/d以内。

IOM报告指出，尽管数十年来医学界不断呼吁限制钠盐摄入，目前美国人均每日钠摄入量仍超过3,400 mg(相当于1.5茶勺的盐)。

发布这篇报告的委员会主席、宾夕法尼亚大学公共卫生与预防医学教授Brian L. Strom博士指出：“我们发现，关于钠摄入量对多数直接健康结局的有益或有害影响，缺乏一致证据的支持。”该委员会并未就钠摄入量的理想目标范围提出确切建议。

Strom博士及其同事回顾分析了2003~2012年间评估钠摄入量对心脏病、死亡等结局的影响的医学研究。尽管这些研究在质量、方法和数据采集等方面存在较大差异，但报告作者还是得出了多项结论：

·高钠水平与心脏病风险之间呈正相关，这与既往有关钠对血压影响的研究结果一致。

·由于缺乏足够数据，尚不能确定将钠摄入量降至2,300 mg/d以下是否会增加或降低心脏病、卒中或死亡风险。

·对于正在接受积极治疗的中、晚期心力衰竭患者而言，钠摄入量≤1,840 mg/d有可能增加不良健康效应(如心血管事件或死亡)的风险。

·各项健康结局研究提供的有关低钠摄入对糖尿病、肾病及心脏病患者影响的证据非常有限，提示这些患者可以遵循针对一般人群的建议。

不过一些专家对上述建议持保留意见。约翰霍普金斯大学Welch预防、流行病学与临床研究中心主任Lawrence Appel博士在接受采访时指出，IOM报告纳入了“存在诸多问题的低质量研究”，而且并未纳入有关减钠对血压影响的证据，而高血压恰恰是健康的关键决定因素之一，也是最重要的可干预性全球死亡危险因素。

Appel博士表示仍支持HHS膳食指南的建议，他本人也参与了这一指南的制订。“中老年人、非裔美国人以及高血压、糖尿病和慢性肾病患者是血压相关心脏病和卒中的最高危人群，将钠摄入量限制在1,500 mg/d以下能够使他们获益。”

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By: KAREN BLUM

Americans should lower sodium consumption to optimize their health – but not below levels of 2,300 mg per day, according to a new report from the Institute of Medicine.

People aged 51 years and older, African-Americans, and those with hypertension, diabetes, or chronic kidney disease can follow the same advice, according to authors of the report, released during a webinar May 14.
 
That recommendation is a departure from the current Dietary Guidelines for Americans from the U.S. Department of Health and Human Services, which recommends that these higher-risk groups limit sodium intake to 1,500 mg daily. The HHS guidelines recommend that most other people aged 14-50 years limit sodium intake to 2,300 mg per day.

On average, Americans consume 3,400 mg or more of sodium a day (equivalent to 1.5 teaspoons of salt), despite efforts over the past few decades to reduce sodium consumption, according to the IOM report, which was sponsored by the Centers for Disease Control and Prevention.

"We found no consistent evidence to support an association between sodium intake and either a beneficial or adverse effect on most direct health outcomes," said Dr. Brian L. Strom, George S. Pepper Professor of Public Health and Preventive Medicine at the University of Pennsylvania, Philadelphia, who chaired the committee that released the report.

The committee did not suggest an optimal target range for sodium consumption.

Dr. Strom and his colleagues reviewed medical studies from 2003 to 2012 that evaluated the direct impact of sodium intake on outcomes such as heart disease and death. Although the studies varied widely in the quality of their methodology and data collection, the report’s authors came to the following conclusions:

·There was a positive relationship between higher levels of sodium and risk of heart disease, consistent with previous research looking at sodium’s effects on blood pressure.

·There were insufficient data to determine if lowering sodium intake below 2,300 mg/day conferred any increase or decrease in the risk of heart disease, stroke, or death.

·Sodium intake of 1,840 mg/day or less may increase the risk of adverse health effects such as cardiovascular events or death among people with mid- to late-stage heart failure receiving aggressive treatment.

·Health outcomes studies provide little evidence about the effects of low sodium intake among those with diabetes, kidney disease, and heart disease, suggesting that people affected by these conditions could follow recommendations for the general public.

But the recommendations prompted calls for caution by some health experts.

The IOM report included "weak studies with numerous problems" and did not include evidence on the effects of sodium reduction on blood pressure, "a key determinant of health and the largest determinant of preventable mortality worldwide," Dr. Lawrence Appel, director of the Welch Center for Prevention, Epidemiology, and Clinical Research at Johns Hopkins University, Baltimore, said in an interview.

Dr. Appel said he still supports the recommendations of the Dietary Guidelines, which he helped create. "Middle- and older-aged adults, African Americans, and patients with hypertension, diabetes, and chronic kidney disease are those at greatest risk for blood pressure–related heart disease and stroke," he said, and they stand to benefit from keeping sodium levels to 1,500 mg/day or less.