Salt - too much or too little?

Salt - too much or too little?

有高血壓的患者，低鈉飲食的重要性眾所皆知，然而更低鈉的飲食(少於3克/天)對高血壓患者或是沒有高血壓患者是好還是壞呢？

Lancet近期這文章一刊出後，
Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: a pooled analysis of data from four studies
Lancet; Published Online: 20 May 2016
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(16)30467-6/abstract

引來American Heart Association (AHA)強烈的反擊，
AHA strongly refutes study findings on sodium consumption
http://newsroom.heart.org/_c/573f94682cfac250e4422568/


因為Lancet這文章告訴我們，
「low sodium excretion is also associated with increased risk」

這研究收集了130,000人，收取早上的尿液，測尿鈉，和血壓值，追蹤四年，
11% of participants with hypertension and 4% without experienced the primary outcome, a composite of death, myocardial infarction, stroke, and heart failure.

In hypertensive patients, a sodium excretion rate of at least 7 g/day was associated with increased CV risk (adjusted hazard ratio 1.23), relative to 4–4.99 g/day. A low excretion rate (less than 3 g/day) was also associated with increased risk (HR, 1.34). But in non-hypertensive patients, only low sodium excretion was tied to higher risk (HR, 1.26).

吃重鹹(超過7克鈉/天)相比於4-4.99克鈉，有較不好的影響這能了解。然而，每日吃低於3克鈉，在高血壓或是沒有高血壓者，也會產生危險，就這讓AHA跳腳了。因為，美國政府、WHO或是AHA，都是建議每日低於 2.3 克鈉以下。若依這研究結果，那以上這3個單位不就是致人民於危險建議之中？

The U.S. government recommends no more than 2,300 milligrams a day, and the World Health Organization recommends 2,000. Unfortunately, most Americans consume more than twice the American Heart Association’s recommended limit of 1,500 milligrams per day.

因此AHA非常大力攻擊這篇Lancet文章，說它是

1) “This is a flawed study and you shouldn’t use it to inform yourself about how you’re going to eat,” said Mark A. Creager, M.D., president of the American Heart Association

2) “This study offers no credible evidence that lower sodium intake can be harmful.  And many other well-done studies support the recommendation of the association to limit daily sodium intake to 1500mg per day,” said Daniel W. Jones, MD. past president, American Heart Association;

3) “Low sodium excretion, based on spot urine collections, is a misleading measure of usual dietary intake over a lifetime,” Dr. Creager added. “Other factors, beyond dietary sodium intake, are present and probably are responsible for the association of lower sodium excretion with cardiovascular disease – factors such as reduced calorie intake, low physical activity, or a concurrent illness.”

敢讓這文章上Lancet的總編輯，真是很有guts，勇於讓不同的研究結果讓全世界看到，當然也要承受來自四方的壓力，尤其是AHA。

但是孔子就說過了，「過猶不及」，也許太低(3 g/d)和太高的鈉對人體都是不好的。目前也沒有訂出每日鈉攝取下限，真的是the lower, the better 嗎？讓我們繼續看下去。