U.S. researchers say they have found a substantial link between increased levels of nitrates in the environment and in food and increased deaths from Alzheimer's, Parkinson's and Type 2 diabetes.

The study, published this month in the Journal of Alzheimer's Disease, found "strong parallels" between age-adjusted increases in the death rate from those diseases and the progressive increases in human exposure to nitrates and nitrosamines through processed and preserved foods, as well as through fertilizers.

The researchers said they recognize that an increase in death rates is anticipated in higher age groups.

Yet when the researchers compared mortality from Parkinson's and Alzheimer's disease among 75 to 84 year olds from 1968 to 2005, they said the death rates increased much more dramatically than for cerebrovascular and cardiovascular disease, which are also aging-associated.

For example, in Alzheimer's patients, the death rate increased 150-fold. However, mortality rates from cerebrovascular disease in the same age group declined, even though this is a disease associated with aging as well.

"We have become a nitrosamine generation," said lead researcher Dr. Suzanne de la Monte of Rhode Island Hospital. "In essence, we have moved to a diet that is rich in amines and nitrates, which lead to increased nitrosamine production," she said.

"We receive increased exposure through the abundant use of nitrate-containing fertilizers for agriculture," de la Monte said.

Nitrosamines are chemical compounds, most of which are carcinogenic, and are produced when the food preservative nitrite combines with amino acids in the stomach.

Nitrate is used mainly in inorganic fertilizers, and sodium nitrite is used as a food preservative, especially in cured meats.

The compounds are also found in cheese products, beer and water. Exposure also occurs through manufacturing and processing of rubber and latex products, as well as fertilizers, pesticides and cosmetics.

"Nitrites and nitrates belong to a class of chemical compounds that have been found to be harmful to humans and animals," the researchers said. "More than 90 per cent of these compounds that have been tested have been determined to be carcinogenic in various organs."

Sharp jump in nitrogen-containing fertilizer use

The researchers graphed and analyzed mortality rates, and compared them with increasing age for each disease. They then studied United States population growth, annual use and consumption of nitrite-containing fertilizers, annual sales at popular fast food chains, and sales for a major meat processing company, as well as consumption of grain and consumption of watermelon and cantaloupe.

The melons were used as a control since they are not typically associated with nitrate or nitrite exposure.

The findings indicate that while nitrogen-containing fertilizer consumption increased by 230 per cent between 1955 and 2005, its usage doubled between 1960 and 1980, which just precedes the insulin-resistant epidemics the researchers found.

They also found that sales from the fast food chains and the meat processing company increased more than eight-fold from 1970 to 2005.