By Joe Dziemianowicz / New York Daily News

Milk is good for bones, but joints are another story for some people, according to a new study.

A strain of bacteria commonly found in milk and beef may be a trigger for developing rheumatoid arthritis (RA) in individuals who are genetically at risk, according to researchers at the University of Central Florida.

The bacteria — mycobacterium avium subspecies paratuberculosis, or MAP — is found in about half the cows in the United States. The bacteria can be spread to humans through consumption of infected milk, beef and produce fertilized by cow manure.

The new UCF findings by infectious disease special Saleh Naser and rheumatologist Shazi Beg, published in the journal Frontiers in Cellular and Infection Microbiology, are the first to connect the dots between MAP and RA, an autoimmune disease that attacks joints, muscles, bones and organs and affects 1.5 million U.S. adults.

The research was inspired by — and builds upon — previous work by Naser that linked MAP with the chronic inflammatory condition of the gastrointestinal tract Crohn’s disease.

“Here you have two inflammatory diseases, one affects the intestine and the other affects the joints, and both share the same genetic defect and treated with the same drugs. Do they have a common trigger? That was the question we raised and set out to investigate,” Naser said.

Beg recruited 100 of her patients for the study. Subjects volunteered clinical samples for testing. Of the patients with rheumatoid arthritis 78 percent were found to have a mutation in the PTPN2/22 gene, the same genetic mutation found in Crohn’s patients, and 40 percent of that number tested positive for MAP.

“We believe that individuals born with this genetic mutation and who are later exposed to MAP through consuming contaminated milk or meat from infected cattle are at a higher risk of developing rheumatoid arthritis,” Naser said.

Researchers said that further study is needed.

“We don’t know the cause of rheumatoid arthritis, so we’re excited that we have found this association,” Beg said. “But there is still a long way to go. We need to find out why MAP is more predominant in these patients — whether it’s present because they have RA, or whether it caused RA in these patients. If we find that out, then we can target treatment toward the MAP bacteria.”