Blood pressure fell equally at all levels of readings, according to averaged results from 38 populations. So, better antihypertensive medication made no detectable contribution to the population decline in blood pressure in the mid-1980s to mid-1990s, say the authors.

The drop is welcome news, since blood pressure is known to be a key risk factor for coronary heart disease -- but scientists have not been able to explain why the change has occurred.

38 Populations, 21 Countries

There are two possible patterns of blood pressure fall in the population: In one, doctors target people with high readings for treatment, leaving others alone. In the other -- mass population change triggered by dietary, lifestyle or environmental factors -- middle and low readings decline as well.

Both patterns will effect change the population average.

Researchers wanted to know whether blood pressure levels fell due to mass population change or due to the use of drugs. They analyzed patterns of blood pressure decline, pooling results collected across 38 populations in 21 countries from the mid-1980s to mid-1990s in the World Health Organization MONICA study.

Pervasive, Powerful and Mysterious

Blood pressure fell equally at all levels of readings, according to averaged results from the 38 populations. So, better antihypertensive medication made no detectable contribution to the population decline in blood pressure in the mid-1980s to mid-1990s, say the authors.

Determinants of blood pressure decline other than medication must have been more pervasive and powerful in the population as a whole during that decade, they suggest, but they cannot say exactly what these factors were.

These findings do not deny the importance of antihypertensive medication in the individual, but are important in understanding blood pressure as a challenge to public health, the authors conclude.