Monday, September 9, 2013

Chloride & Heart Disease - Overlooked & Misunderstood? Low Chloride Levels (Below 100meq/L) Are Associated W/ 20% Increased All Cause Mortality in Hypertensive Subjects

Salt is a four-letter-word today - literally and figuratively; and so would be NaCl, if it was a word and not the combination of the acronyms for natrium, or as Americans like to all it "sodium", and chloride and that despite the fact that low Cl may put your life at risk.
From my previous articles and Facebook posts on the questionable usefulness of dietary salt restriction you will remember that several epidemiological studies have already shown that a very low salt intake can be associated with increases in cardiovascular and all cause mortality. In NHANES I, for example, total sodium intake was inversely associated with all-cause (p=0·0069) and CVD mortality (Alderman. 1998)

You may also have heard me say and write that some scientists have suggested that we should better focus on the chloride rather than the sodium atom in NaCl, if we wanted to rid ourselves of the hypertension problem we are facing these days. Against that background, it sounds somewhat surprising that Linsay McCallum and her colleagues from the BHF Glasgow Cardiovascular Research Centre at the University of Glasgow found that low (not as other scientists suggested high) chloride levels are associated with a +20% increase in all-cause, cardiovascular and noncardiovascular mortality in patients with (pre-)hypertension.

Na(+) >135 & Cl(−) >100 = best survival rate

Among the study subjects, those with Na+ values of more than 135mEq/L, but lower Cl- levels of less than 100mEq/L in the blood, were the ones with the highest (+21%) mortality risk:
Figure 1: Associations of serum chloride, natrium, potassium and HCO2 with systolic and diastolic blood pressure as well as risk of all-cause, cardiovascular disease, ischemic heart disease, stroke and non-CVD mortality risk (McCallum. 2013)
If you take a closer look at the data in figure 1, you as a well-versed SuppVersity reader will albeit also recognize that the main, because only correlate of both systolic (that's the upper value that's supposed to be below 130) and diastolic (that's the lower level that's supposed to be around 80) is neither sodium, nor chloride. It's  HCO3 - or bicarbonate!
Did you know that soccer players lose ~3.4g of chloride (ca. 6g NaCl = salt) and less than 500mg of potassium during a 90 minute pre-season training session (Maughn. 2004)?
Not surprising for you, I know, but still worth highlighting, also because it has been a couple of weeks since I have been writing about the benefits of sodium-bicarbonate and maintaining a healthy acid-base ratio.

There are still many questions to be answered

Excerpt from the researchers' press release: "Sodium is cast as the villain for the central role it plays in increasing the risk of high blood pressure, with chloride little more than a silent extra in the background. [...] However, our study has put the spotlight on this under-studied chemical to reveal an association between low levels of chloride serum in the blood and a higher mortality rate, and surprisingly this is in the opposite direction to the risks associated with high sodium [...] It is likely that chloride plays an important part in the physiology of the body and we need to investigate this further." (co-author Jeemon Panniyammakal)
As Mc Callum et al. point out, there is still a lot of research to be done (including whether similar associations can be observed in hitherto healthy individuals), but as of know it does in fact appear as if ...
"[...s]erum Cl − is a marker of risk that appears to be dissociated from serum Na +and HCO 3 − levels. The underlying mechanism for this risk is unclear. A simple explanation would be that serum Cl − reflects abnormal physiology better than serum Na + , levels of which are perhaps more homeostatically regulated than Cl−" (McCallum. 2013)
Against that background, it is somehwat unsettling that serum chloride levels are not part of the current routine clinical screening (not even in patients with hypertension), so that levels in the "danger zone" between the current lower limit of 95 mEq/L and 100mEq/L could go unnoticed unnoticed for years.

So what do these findings tell us? While the study has been done in hypertensive individuals, I personally feel that the results still support what I have been telling you before about the salt requirements of people who belong to the minority of those who are not yet living on convenience and fast food and work out (and sweat) regularly.

In this regard, the study at hand provides further evidence that falling for the "salt" (=NaCl) restriction propaganda you are exposed to on a daily basis will do more harm than good to someone like you, whose "paleo-ish" diet may cover your bicarbonate needs, but may put you in a similar position as our ancestors, when it comes to the availability of dietary salt - a scarcity that is at the heart of the "salty tooth" we have conserved till today.
References:
  • Alderman MH, Cohen H, Madhavan S. Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I). Lancet. 1998 Mar 14;351(9105):781-5.
  • Maughan RJ, Merson SJ, Broad NP, Shirreffs SM. Fluid and electrolyte intake and loss in elite soccer players during training. Int J Sport Nutr Exerc Metab. 2004 Jun;14(3):333-46.
  • McCallum L, Jeemon P, Hastie CE, Patel RK, Williamson C, Redzuan AM, Dawson J, Sloan W, Muir S, Morrison D, McInnes GT, Freel EM, Walters M, Dominiczak AF, Sattar N, Padmanabhan S. Serum Chloride Is an Independent Predictor of Mortality in Hypertensive Patients. Hypertension. 2013 Aug 26. [Epub ahead of print]