Global incidence of hypertension is increasing

A new study estimated the change in blood pressure in the global population, and the mortality associated with this change for the period from 1990 to 2015. The authors performed a meta-analysis of a large number of studies that examined blood pressure and deaths associated with high blood pressure for populations in various countries:

"In studies from 154 countries that included 8.69 million participants, it is estimated that between 1990 and 2015 the rate of systolic blood pressure (SBP) of at least 110 to 115 mm Hg increased from 73,119 to 81,373 per 100,000 persons, and SBP of 140 mm Hg or higher increased from 17,307 to 20,526 per 100,000 persons.

The estimated rate of annual deaths associated with SBP of of at least 110 to 115 mm Hg increased from 135.6 to 145.2 per 100,000 persons, and for SBP of 140 mm Hg or higher increased from 97.9 to 106.3 per 100,000 persons. Over the past 25 years, the number of individuals with worldwide SBP levels of at least 110 to 115 mm Hg and of 140 mm Hg or higher and the estimated associated deaths have increased substantially."

Focusing on systolic blood pressure (SBP, the higher of the two numbers), researchers found that the number of people with SBP of at least 110 to 115 increased from 73% to 81%, and the number of people with high blood pressure (SBP greater or equal to 140) increased from 17.3% to 20.5%. Along with this increase in blood pressure, there was an increase in the number of deaths associated with high blood pressure from 97.9 to 106.3 per 100,000 people (roughly a 10% increase).

Figure 1 shows a breakdown of the medical conditions associated with hypertension. As described previously, increased blood pressure (BP) damages the blood vessels which can lead to atherosclerosis, as well as other circulatory problems. Not surprisingly, the vast majority of the associated conditions are cardiovascular problems such as heart disease or stroke. High blood pressure also confers a higher risk for chronic kidney disease.

Interestingly the disease burden, measured by disability-adjusted life-years, peaks slightly above SBP = 140 which is the threshold for the high blood pressure classification (Figure 1). However there is a considerable amount of disease burden for those with SBPs between 120 and 140 demonstrating that being above the normal range of 90-120 carries risk even if you do not officially have hypertension.

As an aside, Disability-Adjusted Life-Years (DALY) "is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death" (Wikipedia). There is a simple formula for DALY:

DALY = YLL + YLD

YLL = N x L, where N = number of deaths due to condition, L = standard life expectancy at age of death (expectancy - age at death). This term represents the contribution of early death to disease burden.

YLD = I x DW x L, where I = number of incident cases in the population, DW = disability weight of specific condition, and L = average duration of the case until remission or death (years). The key term is the disability weight (DW) which is larger for more debilitating diseases. For example, the DW for Alzheimer's Disease is 0.666, whereas DW = 0.03 for the amputation of a finger.

Thus, DALY is the combination of years lost to early death plus years in which quality of life is degraded by disability or ill-health.

Returning to the article, what is the cause for the increased global blood pressure?

As an individual, the causes of high blood pressure include smoking, obesity, lack of exercise, too much salt in diet, too much alcohol consumption, stress and older age (WebMD). From a global perspective, the prevalence of smoking, sodium intake, and alcohol consumption have been relatively stable in most countries. What has changed is the increase in obesity, more people (in cities) leading a sedentary lifestyle with insufficient exercise, and an aging population.

There is also a difference between the economically well-off nations versus those that are less wealthy (link): "Between 1980 and 2008, mean age-adjusted SBP declined in economically developed regions such as Australia, North America, and Western Europe and increased in economically developing regions such as Oceania, East Africa, South and South East Asia."

The reason why is that numerous medicines exist to control blood pressure, but many countries do not have access to these drugs because of their expense. I listed previously the different classes of blood pressure lowering medications which include diuretics, beta blockers, calcium channel blockers, and ACE inhibitors (QH). Indeed in the United States there has been improvement controlling high blood pressure (i.e. keeping SBP consistently below 140 with more people receiving blood pressure medications (Reuters):

"Treatment rates increased from about 66 percent in 2003-2004 to about 77 percent in 2010-2012. The proportion of people who got their blood pressure under control increased from 33 percent to 45 percent over the same period."

Hopefully, these medications can be distributed world-wide to help stem the tide of hypertension.

Figure 1. "Projected Global Disability-Adjusted Life-Years by Systolic Blood Pressure Level and Cause, 2015" (from Figure 2 of Forouzanfar et al. (JAMA).