In the United States, consumers’ preference for bottled water over tap water vexes dentists, who worry that their patients aren’t getting enough fluoride to protect their teeth. In Mexico, this question inevitably leads the conversation to salt.
“In Mexico, fluoride is not incorporated into the water,” says Dr. Heriberto Vera, chief of oral health for the Mexican government’s Ministry of Health. “The only systemic distribution method is through table salt.”
He and other health experts agree that in Mexico the trouble is more likely to be too much fluoride, which can lead to a medical condition called fluorosis. It is not added to salt in Aguascalientes, Baja California Norte, Durango, Guanajuato, Zacatecas, and parts of Jalisco, where fluoride occurs naturally in the water table. Dr. Gerry Eijkemans of the Mexico office of the Pan American Health Organization (PAHO), the Latin American-Caribbean branch of the WHO, explains: “If you don’t have enough, it’s bad for your teeth, but if you have too much it can also cause problems with your teeth and with your bones.” The recommended maximum concentration is 0.7 milligrams per liter of water, or 250 milligrams per kilogram of salt.
There’s no question that fluoride is good in the appropriate quantities. According to Mexico City dentist Pablo Zimbron, “[in] the right amount it’s beneficial because it changes the structure of the dental enamel,” especially in children under age eight.
According to Vera, the health department closely monitors the concentration and distribution of fluoride levels nationwide and makes sure it’s consumed in safe quantities by adjusting or eliminating the levels added to salt from region to region: “It’s a very narrow range, difficult to achieve,” he says.
Bottled-water companies do not fluoridate their product, and the reverse osmosis purification method they employ, as required by health department regulations, removes any naturally occurring fluoride, says Roberto Contreras, chief of potability and treatment for CONAGUA, the Mexican government’s federal water commission.
Since 2005 all salt for human consumption must be labeled with its iodine and fluoride content, says Vera, who helped develop the guidelines for Mexico. The WHO has declared the three best delivery methods for fluoride to be through water, salt, or milk. In Mexico most people don’t drink the tap water, so it is not an effective method of delivery, but just about everyone uses salt — on average eight grams per day each — so it is the logical way to deliver fluoride. Fluoride is also present in many toothpastes.
Fluoride was first added to salt in the Estado de México in 1988, Vera says, with the rest of the country following suit in 1993. These days the health ministry is busy studying water supplies to find out where there is too much fluoride and then limiting or eliminating fluoridated salt in those areas.
Vera says this and other oral health measures have had a tangible effect, with a 56% reduction in cavities over ten years.
Other too-much-of-a-good-thing contaminants that frequently accompany fluoride in water are manganese and iron. In the majority of cases tap water is safe to drink, Contreras says, but adds that although the water may be fine, storage tanks and the pipes it flows through might not be. Tanks can hold dirt and rust, or may be infested with bugs or bacteria.
“We are trying to enable people to consume a liquid of appropriate or adequate quality,” says Contreras. “We are investing and trying to give the population water of quality for use and human consumption and prevent health damage.”
Theresa Braine, a freelance journalist based in Mexico City, covers public health, among other topics. She has written for People, the World Health Organization and Newsday.