Academic journal article Bulletin of the World Health Organization

Understanding the Decline of Mean Systolic Blood Pressure in Japan: An Analysis of Pooled Data from the National Nutrition Survey, 1986-2002/comprendre la Baisse De la Pression Systolique Moyenne Au Japon: Analyse Des Donnees Rassemblees a Partir D'enquetes Nationales Sur la Nutrition, 1986-2002/razones De la Disminucion De la Presion Arterial Sistolica En El Japon

Academic journal article Bulletin of the World Health Organization

Understanding the Decline of Mean Systolic Blood Pressure in Japan: An Analysis of Pooled Data from the National Nutrition Survey, 1986-2002/comprendre la Baisse De la Pression Systolique Moyenne Au Japon: Analyse Des Donnees Rassemblees a Partir D'enquetes Nationales Sur la Nutrition, 1986-2002/razones De la Disminucion De la Presion Arterial Sistolica En El Japon

Article excerpt

Introduction

Control of systolic blood pressure (SBP) is an important public health issue because elevated SBP is one of the independent risk factors for cardiovascular disease (CVD). (1-3) CVD is a leading contributor to the global burden of disease, accounting for 28% of 50 million deaths and 13% of 1.4 billion disability-adjusted life years in 2001. (4) Several prospective cohort studies revealed that lower SBP at baseline is associated with reduced CVD mortality and incidence. (2,3,5) It has been reported that even a decline of SBP at baseline by 2 mmHg is related to a reduction of 16-year mortality from CVD by 5%. (6) Effective control of SBP is thus essential for improving population health.

However, the global trend of hypertension has been worsening. The estimated global prevalence of hypertension was more than 25% among adults in the year 2000 and it is projected to rise, especially in developing countries, between 2000 and 2025. (7) It is also noteworthy that mean SBP in the United States of America decreased during the 1970s and 1980s, but the trend has stagnated since the 1990s. (8-10)

A declining trend of mean SBP has been observed in several general populations, including Japan. (8,11-15) Understanding why mean SBP has been decreasing in these populations is crucial for public health policy. Although population-wide and personal interventions might have been effective, the factors that actually contributed to the decline of mean SBP have not been investigated yet, largely due to the lack of longitudinal data based on a nationally representative sample. According to two previous studies of how individual SBP is distributed in the population and how the distribution had shifted over time, changes in population-wide behaviours and environmental conditions made a larger contribution to the trend than improved treatments. (16,17) However, the nature of the cross-sectional survey data that were used in these studies precluded further quantification of the contributions of individual factors.

Japan has experienced a remarkable reduction in mean SBP since the late 1960s. (12,13,15,18) A study using published summary statistics attributed the decline of mean SBP between 1965 and 1980 to the improved treatment rate of CVD. (15) However, so far no one has examined why mean SBP further decreased since the 1980s in Japanese adults for which individual-level data on SBP and the use of antihypertensive medications are electronically available.

The objective of this study was to explore the factors linked to the decline of mean SBP and evaluate their individual contributions by using a statistical model to address potential treatment bias in cross-sectional data and thereby obtain useful information for public health policies. Pooling data of nationally representative annual surveys in Japan between the mid 1980s and the early 2000s, this study assessed the relationships between the change in mean SBP and changes in the use of antihypertensive treatment and lifestyle factors in Japanese adults.

Methods

Data sources

We used microdata of the National Nutrition Survey (NNS), which is a cross-sectional interview and examination survey conducted on a nationally representative sample every November by the Ministry of Health, Labour and Welfare. This survey aims at obtaining basic data on anthropometry, nutritional intake and diet, and lifestyles to establish measures for nationwide health promotion. (19) The methods of the NNS have been described in detail elsewhere. (20) Eligible respondents included all residents aged 1 year and older in 300 census tracts that were randomly selected from around 900 000 census tracts. Response rates of the NNS were estimated to be 60-70%, (21) and the sample was considered representative of the Japanese population. (22)

In the NNS, all household members were asked to participate in physical examinations at a local community centre near their residence on a specific day during the survey period. …

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