The Pharmaceutical Journal Vol 264 No 7085 p332
February 26, Letters

Dietary advice

Different ethnic responses to reduced salt intake

From Ms M. R. Hook, MRPharmS

SIR,—The dietary advice tips on hypertension had a serious omission (PJ, February 19, p285). The paragraph about reduced salt intake failed to mention ethnic differences in response to this intervention.
In the article by N. Kaplan on ethnic aspects of hypertension (Lancet 1994:344;450-2), the increased sodium sensitivity of black African patients when compared with white patients is highlighted.
Black African patients show a marked suppression of aldosterone release despite strong renin-angiotensin stimulation which may reflect chronic volume expansion as a result of renal sodium retention. This leads to a greater lowering of blood pressure in response to a modest reduction in sodium intake (down to 100mmol/day).
There are also marked differences in their response to antihypertensive drug therapy. Mono therapy with drugs which suppress the renin-angiotensin system (ie, beta-blockers and ACE inhibitors) does not produce the expected response. However, they respond equally well to diuretics, central alpha-agonists, and calcium channel blockers. If a low dose diuretic such as bendroflumethazide (bendrofluazide) is added to either beta-blocker or ACE inhibitor therapy then the response is similar to non-black patients.
The message is to encourage salt restriction. Yes, sorry, but that does include salt-cod, a favourite for some. Another message is to look carefully when dispensing beta-blockers or ACE inhibitors for black African patients to check they are also taking diuretics. If they are not, a message to the general practitioner may improve their blood pressure control.
The updated British Hypertension Guidelines published in the BMJ in September, 1999, also suggest multiple therapy with lower doses to minimise side effects and maximise control of hypertension.

Margaret Ruth Hook
Bristol

Dr PAMELA MASON replies: Blood pressure is a complex process influenced by many cultural, social and behavioural factors, and the relationship between salt and blood pressure is a long-standing question. Although the influence of salt on blood pressure may have been overstimated in the past, there is some consensus that a diet low in sodium and high in potassium (together with the other factors mentioned in the dietary advice tips on hypertension) is associated with the development of hypertension.
However, as your correspondent points out, studies have shown a greater prevalence of "salt sensitivity" in black patients compared with whites. The reasons for this are not entirely clear. Renal abnormalities induced by hypertension, reduced Na+/K+-ATPase pump activity, other ion transport disturbances and increased insulin resistance have been suggested to play a role.¹ The differences in reponse of black patients to antihypertensive drug therapy (pointed out in the letter) are consistent with a higher prevalence of salt sensitivity in blacks compared with whites.²
In addition, the prevalence of salt sensitivity in the non-black population is not known. Because blood pressure response to salt restriction is heterogenous, individuals in any population may react to salt reduction differently.
The individual patient should always be considered. This, after all, is at the core of pharmaceutical care. However, there is no known hazard to moderate salt restriction and as your correspondent states, salt restriction should be encouraged.

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