Nitrites in Meats Fingered in Rise of Diseases
July 15, 2009 -- The rising rate of diabetes, Parkinson's disease, and Alzheimer's may be linked to nitrites and related compounds -- found in hot dogs, bacon, potatoes and fertilizers, among other common products.
Nitrites are already known to cause cancer. A new study suggests that low doses of these chemicals can also have serious effects on the brain, that certain age-related diseases are caused by more than just aging, and that there might be simple things people can do to help prevent them.
The link is still in the hypothesis stage, experts say, and there's unlikely to be just one explanation for a host of complicated diseases. Still, lead author Suzanne de la Monte is already making efforts to avoid nitrates herself.
"I think it's really important for people to take steps into their own hands," said Suzanne de la Monte, a neuropathologist at Rhode Island Hospital and Brown University's Medical School in Providence. "You need to be really careful to avoid this stuff as much as possible."
Sodium nitrite is used to preserve and color fish, meat, and other processed foods, especially hot dogs and bacon. Nitrates are often found in fertilizers and end up on produce, particularly root vegetables such as potatoes and beets.
In the acidic conditions of the stomach or when cooked over high heat, nitrates and nitrates can be converted to nitrosamines, which are potent cancer-causing chemicals. Nitrosamines are also formed as byproducts of certain industries, such as rubber and latex.
De la Monte had worked with a nitrosmaine-like drug called streptozotocin (STZ), which scientists use in animal experiments to cause Alzheimer's disease as well as diabetes mellitus and a liver disease called NASH. All three of these illnesses involve resistance to insulin, a hormone that helps break down sugar.
She wondered if nitrosamines in the environment might be doing the same thing to people that STZ was doing to lab animals.
She and colleagues started by collecting data about the use of nitrites and nitrates in fertilizers, fast food, meat and grains over the last few decades. Then, they looked at a national health database dating back to 1965 to find out how many people were dying from which diseases and at what ages, and how those numbers had changed.
Analyses showed that exposure to nitrates has indeed gone up. Sales at a fast food franchise and at a major meat processor have jumped by a factor of eight since 1970. And the use of nitrogen-containing fertilizer doubled between 1960 and 1980, right before outbreaks of insulin-resistant epidemics, including diabetes and Alzheimer's, picked up.
The new study, which appeared in the Journal of Alzheimer's Disease, also found that the probability of dying from Alzheimer's is far higher today than it was in 1965 for every age group. That rise in death risk was steeper with increasing age, suggesting that a longer period of exposure to the implicated chemicals made the problem worse.
Diabetes and Parkinson's showed similar patterns, even though drugs have been getting better and even though rates of other age-related diseases have been dropping.
Together, de la Monte said, the data strongly suggest that the rising rates of death from Alzheimer's, Parkinson's, and diabetes are due not to genes or an aging population, but to exposure to nitrosamines.
"It was so shocking," de la Monte said. For "ages," she said, doctors have been taught that these diseases were determined by genetics. "This clearly shows it couldn't possibly be genes."
The theory is intriguing and worth pursuing, said neurotoxicologist Deborah Cory-Slechta, but it's far too soon to blame nitrosamines alone for Alzheimer's and other age-related diseases. Scientists haven't yet documented rising rates of nitrosamines in our bodies, for one thing. And the theory may be too simplistic.
"Lots of other things changed in that time frame that aren't being taken into account," said Cory-Slechta, of the University of Rochester School of Medicine and Dentistry in New York. "I don't think most of these kinds of complicated diseases are caused by a single factor of any kind."
