As soon as they saw the empty truck brake suddenly on the deserted rural highway, the four men in dark-blue uniforms jumped into action.
The truck likely was a scout, slowing to phone a warning to smugglers close behind. Piling into a white van, the officers roared down the two-lane road until they found a heavily laden truck struggling to turn around to avoid the police trap.
"We got him just after he got the call on his cell phone," said Li Yanming, recounting the chase in China's northern Ningxia region. On board, the officers found 14 tons of white powdery contraband -- salt.
Li and his colleagues are salt police, 25,000 officers with red epaulets and gold badges in the shape of salt crystals who enforce one of the oldest economic policies in the world: the Chinese government's exclusive right to produce and sell salt.
Although China first imposed the salt monopoly 2,600 years ago, the police force was created just eight years ago to help fulfill a modern public health goal.
In 1994, China launched a national campaign to fortify all salt with iodine, needed for healthy brain development in fetuses.
The salt police were set up to enforce the monopoly, shutting down hundreds of private producers and merchants who had appeared during the market reforms of the 1980s. The officers also patrol remote regions like Ningxia, where smugglers sell poor people illegal salt that is cheaper, but not iodized.
As is often the case under the communist regime, the tactics are heavy-handed. But experts say they have helped China achieve one of the biggest health successes in recent history.
By 2000, 90% of China's 1.3 billion people were eating iodized salt, up from 10% in the 1980s. That means that more than 18 million of the 20 million children born annually in China have a better chance of good brain development. By contrast, iodized salt accounts for only 70% of consumption in the United States, which started adding the mineral to salt in the 1920s to prevent goiter. That was before the link with mental development was known.
As recently as the 1980s, researchers were finding entire villages just miles from Beijing where the average IQ was 60, well below the norm of 100. A third of villagers suffered from cretinism, a severe form of mental retardation that often involves stunted growth as well as loss of speech and hearing.
More than 80% of the 10 million mentally disabled people in China are victims of iodine deficiency, said Wang Zhilun, a researcher on endemic diseases at Xi'an Medical School in Shaanxi province.
Studies in China in the 1980s and early '90s by foreign and Chinese scientists were among the first to establish the connection between iodine and brain development. They found that just a teaspoonful consumed over a lifetime prevented cretinism and raised IQs by 10 to 15 points.
China's success with iodine is a lesson in what it takes to get things done in this increasingly freewheeling, market-driven society. Resistance by underfunded local governments was overcome only by a push from the central leadership.
After years of lobbying by health officials, the breakthrough came at a 1993 conference in Beijing attended by then-Vice Premier Zhu Rongji, said Glen Maberly, a researcher who was at the conference.
Maberly, now a professor of international health at Emory University in Atlanta, says the researchers repeatedly told Zhu that China was losing tens of millions of IQ points a year.
"At one point, Zhu said, 'We will solve this problem,' " recalled Maberly. "And that's what it took."
The following year, the government revived the salt monopoly, which, although officially still in effect, had fallen into neglect during the market openings of the 1980s. Salt monopolies have existed in China off and on since the 7th century B.C., when emperors first used salt revenues to finance strong central government.
Since 1994, China has spent more than $100 million to install iodine-adding technology at salt mills and improve distribution by state-owned salt companies.
The newly created salt police are controlled by each region's state-run salt companies -- an unusual arrangement that gives a producer the power and incentive to go after smugglers.
The result: Iodine deficiency was quickly eliminated in the cities and many densely populated eastern provinces.
"The monopoly has caused higher prices, but it was necessary to get the salt into iodine-deficient areas quickly," said Chen Zupei, a Ministry of Health advisor.
The monopoly has struggled, however, in areas where natural salt is cheap and abundant, or where local governments continue to be indifferent.
In Ningxia, officials estimate that only a fifth of salt is bought from the monopoly. The rest is smuggled in from neighboring Shaanxi and Inner Mongolia, which have vast salt lakes.
Residents of this wind-swept region of grasslands and cattle and goat herds welcome the smuggled salt because it costs 1 mao (13 cents) a pound -- one-ninth the salt monopoly price.
Most smuggled salt crosses Yanchi, an eastern county that borders Shaanxi and Inner Mongolia. Sixteen salt police officers patrol its 2,850 square miles, spending most of their time in ambush along lonely roads, scanning every passing vehicle.
Yang Xingjun, 51, was captured near the village of Huianbao, where the blacktop highway and crumbling remains of the Great Wall are the only features visible on the endless plains.
A former farmer who made less than $60 a year coaxing cabbage and potatoes from dry earth, Yang said in an interview that he jumped at the chance to earn $50 a night driving a salt truck in from Inner Mongolia.
He said he knows of iodine's benefits from state education campaigns. But health is a luxury that Ningxia's poor can't afford.
"We have no money," Yang said. "We can't worry about these things like city residents can."