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(Hypertension. 1999;34:e11.)
© 1999 American Heart Association, Inc.

Letters to the Editor

Study Duration and Validity

Alexander G. Logan, MD

Senior Scientist,, Samuel Lunenfeld Research Institute Mount Sinai Hospital, Toronto, Ontario, Canada

	Introduction

 
Letter to the Editor:

At the NHLBI workshop on sodium and blood pressure held on January 28–29, 1999, to re-examine the US recommendation on sodium intake for healthy people, two meta-analyses addressing this issue were harshly criticized for including randomized clinical trials of less than 2 weeks duration. It was argued that their inclusion invalidated estimates of the blood pressure lowering potential of a sodium-restricted diet. This viewpoint has been expressed before in letters to the editor¹ and in editorials.^{2 3} Yet, Hypertension continues to publish short-term intervention studies such as that by He et al, which compared the effects of a 5-day low sodium diet (10 mmol/d) on the blood pressure of black and white hypertensive subjects.⁴ For researchers interested in pooling data, these mixed messages from experts in the field create confusion. Should they heed the comments made about the scientific validity of short-term trials^{1 2 3} or merely view them as criticisms leveled at meta-analyses with findings that differ substantially from the critics’ own assessment of the evidence?

	References

 
1. Whelton PK, Cohen JD, Applegate WB. Dietary sodium and blood pressure. JAMA. 1996;276:1467–1468.

2. Lenfant C. High blood pressure: some answers, new questions, continuing challenges. JAMA. 1996;275:1604–1606.[Abstract/Free Full Text]

3. Kaplan NM. Primary hypertension: from pathophysiology to prevention. Arch Intern Med. 1996;156:1919–1920.[Abstract/Free Full Text]

4. He FJ, Markandu ND, Sagnella GA, MacGregor GA. Importance of the renin system in determining blood pressure fall with salt restriction in black and white hypertensives. Hypertension. 1998;32:820–824.zkey[Abstract/Free Full Text]

Response

Feng J. He; Nirmala D. Markandu; Giuseppe A. Sagnella; Graham A. MacGregor

St George’s Hospital Medical School, London, England

	Introduction

 

We are grateful to Dr Logan for raising the important topic of how to interpret trials of salt restriction. In relation to the short-term acute studies of changes in salt intake, no one is questioning the validity of these studies; it is the way that they are interpreted that is at issue. They are clearly useful to investigate differences in response, in particular because larger changes in salt intake can be achieved and the study can be better controlled. The study¹ that . . . [Full Text of this Article]