Should you be worried about salt?

AWASH chair­man Bruce Neal, pro­fes­sor of med­i­cine at the Uni­ver­si­ty of Syd­ney, said that despite entreaties to cut salt lev­els, the fast-food indus­try was still “fid­dling around the edges”. This was despite high blood pres­sure being a lead­ing cause of death in Aus­tralia, along­sidesmok­ing.” extract from The Aus­tralian

As some­one diag­nosed years ago with mild hyper­ten­sion, that sort of state­ment sends me off to do a lit­tle research. It turns out that, even if we make allowances for the sim­pli­fi­ca­tions of a press release, this is pret­ty dubi­ous stuff. A half hour of research (repro­duced below), shows that it is sim­ply not true that hyper­ten­sion (high blood pres­sure) is a ‘lead­ing cause of death’ in Aus­tralia and that it is a mat­ter of some con­tro­ver­sy whether reduced salt intake offers sig­nif­i­cant ben­e­fits for the con­trol of blood pres­sure, par­tic­u­lar­ly in the major­i­ty of the pop­u­la­tion who do not have high blood pres­sure.

I first checked the Aus­tralian Depart­ment of Health data (Aus­tralian Health and Wel­fare Institute’s “Australia’s health 2008″) where hyper­ten­sion is nowhere to be found among the top ‘under­ly­ing causes’—the term used in the sta­tis­tics for the main caus­es—of death. Hyper­ten­sion does, how­ev­er, fig­ure on (with­out lead­ing) the list of impor­tant ‘con­trib­u­to­ry’ caus­es of deaths in Aus­tralia. In 2005, accord­ing to the AIWH, “high blood pres­sure con­tributed to more than 14,500 deaths (almost 11% of all deaths, eighth in the ranks of con­trib­u­to­ry caus­es) but was the under­ly­ing cause in only 410 deaths” (in a high­er pro­por­tion of female deaths than male, as it turns out).

So what is the evi­dence on the link between salt intake and the con­trol of hyper­ten­sion? To check, I con­sult­ed the excel­lent (and open access) Cochrane Library of clin­i­cal tri­als. Recent reviews (‘meta-stud­ies’) of a num­ber of high qual­i­ty clin­i­cal tri­als point to at most a small effect on blood pres­sure due to reduced salt intake. This effect appears to be very small (around 1mg of mer­cury pres­sure in the dias­tolic pres­sure) in ‘nor­mal’ peo­ple but greater for peo­ple with high blood pres­sure. One study of long-term effects in 2003 found no evi­dence of a ‘dose effect’ rela­tion­ship between the amount of salt reduc­tion and the size of the reduc­tion in blood pres­sure.

Inten­sive sup­port and encour­age­ment to reduce salt intake did lead to reduc­tion in salt eat­en. It also low­ered blood pres­sure but only by a small amount (about 1 mmHg for sys­tolic blood pres­sure, less for dias­tolic) after more than a year. This reduc­tion was not enough to expect an impor­tant health ben­e­fit. It was also very hard to keep to a low salt diet. How­ev­er, the reduc­tion in blood pres­sure appeared larg­er for peo­ple with high­er blood pres­sure. There was not enough infor­ma­tion to assess the effect of these changes in salt intake on health or deaths. Evi­dence from a large and small tri­al showed that advice to reduce salt helps to main­tain low­er blood pres­sure fol­low­ing with­draw­al of anti­hy­per­ten­sive med­ica­tion. If this is con­firmed, with no increase in car­dio­vas­cu­lar events, then com­pre­hen­sive dietary and behav­iour­al pro­grammes in patients with ele­vat­ed blood pres­sure requir­ing drug treat­ment would be jus­ti­fied.” extract from Hooop­er, Bartlett, Smith et al

Anoth­er study (also from 2003) sum­ma­riz­ing the clin­i­cal tri­als of short term impacts of reduc­ing sodi­um in the diet reached a sim­i­lar con­clu­sion:

The mag­ni­tude of the effect in Cau­casians with nor­mal blood pres­sure does not war­rant a gen­er­al rec­om­men­da­tion to reduce sodi­um intake. Reduced sodi­um intake in Cau­casians with ele­vat­ed blood pres­sure has a use­ful effect to reduce blood pres­sure in the short-term” extract from Jur­gens, G et al

The Hoop­er study (first quo­ta­tion above) of long-term impacts has been coun­tered by a sim­i­lar meta-study by one of the founders of AWASH’s UK affil­i­ate. Mac­Gre­gor et al found, in 2004, that by choos­ing to look at a dif­fer­ent group of tri­al results with dou­ble the aver­age salt reduc­tion of those con­sid­ered by Hoop­er (from 2g/day to 4/g per day), they found reduc­tions of 5mg/hg (sys­tolic) and 2.7mg/hg (dias­tolic) in hyper­ten­sive par­tic­i­pants. But they found only 2.03 mg/hg and 0.99 mg/hg falls in blood pres­sure in nor­moten­sive par­tic­i­pants. They also found a dose-effect.

I am not qual­i­fied in med­i­cine. I offer you no advice what­ev­er about salt in your diet (ask your G.P). But, as a pub­lic pol­i­cy ana­lyst, I observe that even the study that is more favor­able to the ‘salt reduc­tion’ cam­paign, demon­strates very mod­est impacts from cut­ting down on salt in the diet. The aver­age out­come for some­one with nor­mal dias­tolic (the low­er) blood pres­sure read­ings is sim­i­lar in all the stud­ies and bare­ly sig­nif­i­cant (at around 1mg/hg). Based on all three of these stud­ies tak­en togeth­er, I do not see how a cam­paign to change pop­u­la­tion-wide dietary salt lev­els is jus­ti­fied, although some­one with hyper­ten­sion might be bet­ter advised to con­sid­er reduc­ing salt intake.

I make no infer­ences about the bona fides of Pro­fes­sor Neal’s cam­paign. I pre­sume they are the best. But I ques­tion why he is tar­get­ing fast-food chains.

A sur­vey of salt lev­els in lead­ing fast food brands, to be released today by Syd­ney-based health experts, found three-quar­ters of the burg­er and sand­wich-style prod­ucts sold by six com­pa­nies pro­vid­ed more than 50 per cent of the sug­gest­ed dai­ly tar­get. One prod­uct — KFC’s Zinger Dou­ble BBQ Bacon & Cheese Burg­er — pro­vid­ed the high­est amount of salt, with 2410mg of sodi­um per burg­er.”

We know from inter­na­tion­al data as well as from the AIWH reports that the biggest ‘risk fac­tor’ for hyper­ten­sion is… grey hair. It seems unlike­ly that the part of the pop­u­la­tion most at risk of hyper­ten­sive prob­lems, and there­fore best able to take advan­tage of the mod­est ben­e­fits of salt reduc­tion, is load­ing up on salt at these out­lets.

2 Comments

  • Phil Rich wrote:

    Hi Peter,

    I think the thing I’m impressed with is how you have found your way through the mis­in­for­ma­tion morass 🙂 Con­grat­u­la­tions. For you infor­ma­tion, I have had some­thing called lyme dis­ease for 40 years … and it is salt (what doctor’s would call a large quan­ti­ty), com­bined with vit­a­min C spread through­out the day that is cur­ing me where antibi­otics and oth­er treat­ments have been com­plete fail­ures….

    Inter­est­ing, no??

    Regards,

    Phil Rich
    Senior Busi­ness Ana­lyst

  • Glad to hear about the ‘salt cure’ Phil.

    Lyme dis­ease is a ter­ri­ble thing, so I’m delight­ed to hear that there’s a sim­ple recipe that is help­ing you. Do you know of any con­trolled tri­als of salt + vit­a­min C?

    Good luck and thanks for the infor­ma­tion.

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