People diagnosed with celiac disease are almost twice as likely as those without it to break a bone, according to a new review of the evidence.

More studies are needed, though, to see if people whose celiac hasn’t been diagnosed yet are at similar risk, researchers say.

About two million Americans have celiac disease - in which the immune system attacks the small intestine in response to gluten, a protein found in wheat, rye and barley - according to the National Institutes of Health.

For the new review, researchers from the University of Tampere and Seinäjoki Central Hospital in Finland, and the University of Nottingham in the UK analyzed 16 studies that compared the incidence of bone fractures among people with and without a celiac disease diagnosis.

In studies that looked at one point in time, people with celiac disease were almost twice as likely to have had a bone fracture in the past.

In studies that followed people over time, those who had a diagnosis of celiac disease at the start were about 30 percent more likely to suffer a bone fracture and 69 percent more likely to have a hip fracture than others, according to the analysis published in the Journal of Clinical Endocrinology and Metabolism.

There were only two studies of bone fractures among people with undiagnozed celiac disease – but whose blood tests showed celiac-specific antibodies - and it was not clear if there was a link to broken bones, the authors write.

Since the disease affects nutrient absorption in the small intestine, it could lead to poor absorption of vitamin D and calcium, or chronic intestinal inflammation could interfere with bone formation, they write.

Other possibilities to explain the connection to bone breaks include hormonal changes or a gluten-free diet, which is often low in minerals, they write.

Other studies have found that bone density tends to go down as symptoms become worse for people with celiac disease, according to Professor Julio C. Bai at the Hospital de Gastroenterologia Dr. Carlos Bonorio Udaondo in Buenos Aires, Argentina.

“Therefore and based on our findings, it seems reasonable to consider to evaluate bone density in those patients with symptomatic celiac disease,” said Bai, who was not involved in the new study.

Symptoms can include abdominal bloating and pain, chronic diarrhea, constipation and weight loss.

Physical activity can help strengthen bones, he said.

“Some areas of bone are more vulnerable to the damage induced by celiac disease,” said Dr. Peter H.R. Green, an expert on celiac disease at Columbia University in New York who wasn’t involved in the new review. “This relates to the type of bone and its rate of turnover.”

Everyone newly diagnosed with celiac disease is routinely given a bone density scan, as they should be, he told Reuters Health by email.

“We have shown that a gluten free diet together with replacement of calcium and vitamin D, when necessary, results in improvement in bone density,” he said.