Mystery kidney disease linked to global warming

A mysterious kidney disease that has killed over 20,000 people in central America and has also been observed in India and Sri Lanka may be caused by chronic, severe dehydration linked to global climate change, a new study has found.

"This could be the first epidemic directly caused by global warming," said Richard J Johnson, professor at the University of Colorado School of Medicine in US.

"Some districts of Nicaragua have been called the 'land of widows' due to the high mortality rates occurring among the male workers from chronic kidney disease," Johnson said.

The epidemic was first described in 2002 and has been dubbed Mesoamerican Nephropathy. It is most prevalent among manual labourers on sugar cane plantations in the hotter, lower altitudes of Central America's Pacific coast.

Theories abound about what may be causing it, including exposure to heavy metals, pesticides and other toxic chemicals. But Johnson believes the actual culprit is chronic recurrent dehydration. Researchers studied sugar cane workers in Nicaragua and El Salvador and found that the labourers routinely worked in conditions exceeding the recommended heat standards of the US Occupational Safety and Health Administration (OSHA).

Even though some of them drank up to one to two litres per hour, the researchers found they still suffered serious dehydration on a daily basis.

One of the major side-effects of this dehydration was hyperuricemia or excess uric acid levels in the blood.

In one study, sugar cane workers in El Salvador had uric acid levels of 6.6 milligrammes per decilitre in the morning and which increased to 7.2 milligrammes in the afternoon.

Researchers also found that 21 of 23 people with chronic kidney disease CKD had hyperuricemia.

Dehydration also activates a pathway in the kidney which generates fructose that, when metabolised, produces uric acid.

This may contribute to the kidney damage.

Workers who rehydrate with drinks that contain high fructose corn syrup or sugar may be exacerbating the problem due to the high fructose content present in the drinks.

Researchers also found that these dehydrated workers had high concentrations of uric acid crystals in their urine.

This 'sandy urine' is associated with signs of dehydration, including light headedness, elevated heart rates and headache. The uric acid crystals are thought to trigger tubular damage and fibrosis in the kidneys.

The study suggests that this epidemic may be gaining momentum now because global warming is increasing the risk of dehydration.

"Temperatures have been progressively increasing in El Salvador over the last century, with an average increase of 0.5 degrees Celsius since 1980," the study said.

Johnson said that this kind of CKD is now being observed in Sri Lanka, India, Thailand, and Egypt.

The study was published in the American Journal of Kidney Diseases.