To raise awareness of one of the most common, serious, but overlooked medical conditions, World Hypertension Day has been marked on May 17 every year since 1978. Yao Yuxin reports.

Cardiovascular disease kills 17.9 million people every year. As such, it is the number one killer on the planet, accounting for 31 percent of all deaths worldwide annually, according to the website of the World Health Organization.

Moreover, four out of every five of those deaths are caused by heart attacks or strokes, about half of which are the result of hypertension - high blood pressure - the WHO said.

More than 1 billion adults across the globe have high blood pressure, but fewer than one in five patients have the condition under control, according to the website.

The picture is even bleaker in China, where only 15.3 percent of the 245 million people diagnosed with the condition managed to lower their blood pressure to normal levels last year, according to Circulation, a journal that focuses on issues related to cardiovascular disease.

"There is never enough awareness of hypertension, because you can't feel it," said Craig Anderson, executive director of the George Institute for Global Health China, a nonprofit medical research center established in Sydney in 1999, which has offices in Australia, the United Kingdom, China and India.

"It's not something you can feel in your body unless your blood pressure is extremely high - then you get headaches, become flushed and feel dizzy," said Anderson, who is also a professor of neurology and epidemiology at the University of New South Wales.

According to Circulation, the silent nature of the condition means more than half of those affected in China are not aware that they are at risk. The problem is exacerbated because less than half of those diagnosed with the condition take medication to control it.

Anderson estimates that at least 20 percent - and perhaps even 30 percent - of adults worldwide have hypertension. Meanwhile, Circulation reported that the incidence rate in China accounts for 23.2 percent of the adult population, and 41.3 percent are at risk of developing the condition.

Anderson said: "If you look at the number of people in China, that's hundreds of millions of people. It's a big problem."