UB Study Documents Diabetes-Thyroid Disease Link in Maine Native-American Tribe

BUFFALO, N.Y. - University at Buffalo researchers have demonstrated for the first time a close association between hypothyroidism and diabetes mellitus in an American-Indian tribe, and found diabetic women to be particularly at risk.

The study, published in the July issue of the Journal of Family Practice, found that in this tribal population, women with diabetes were more than twice as likely to have hypothyroidism as non-diabetic women.

"It's been more or less known that people with diabetes are more likely to also have poor thyroid function," said Arthur Michalek, Ph.D., UB professor of social and preventive medicine, and lead author on the study. "But the relationship has never been demonstrated in American Indian populations, which are known to have the highest diabetes rates in the world.

"We really don't know why this relationship exists," he said. "There may be some inherent susceptibility to endocrine failure. Clearly, more research is needed to find out what is behind the link." Michalek also is dean of the Graduate Division and director of education affairs at Roswell Park Cancer Institute in Buffalo.

Michalek and colleagues conducted their research at the request of the Passamaquoddy tribe, the "People of the Dawn," at their tribal health center in Eastport, Maine. They reviewed the clinical records of 892 people -- 415 men and 477 women -- eligible for clinical services during 1998, and identified those with a diagnosis of diabetes or hypothyroidism.

Hypothyroidism is a condition in which the thyroid produces too little of the hormones thyroxin, triiodothyronine and calcitonin, which regulate the body's metabolism. Symptoms include fatigue, lethargy and weight gain, which also are symptoms of diabetes. Because

symptoms of the two diseases are similar, physicians often don't explore the possibility of thyroid disfunction once they find diabetes, Michalek said.

Results of the record-review showed that the prevalence of diagnosed hypothyroidism varied greatly by age, gender and diabetes status. The researchers identified 156 cases of diabetes, an incidence of 17.5 percent, and 25 cases of hypothyroidism, or an incidence of 2.8 percent, in the total study population. Among women, 21.4 percent had diabetes and 5 percent had hypothyroidism, which accounted for all but one case. The prevalence among men was 13 percent and .2 percent respectively. The one man who had hypothyroidism also had diabetes, results showed.

The prevalence of hypothyroidism among diabetic women ranged from 5 percent among women under 60 years old, to 21 percent of women over 60. In non-diabetic women, the prevalence by age was 3.7 percent and 9 percent, respectively.

The annual incidence of hypothyroidism in the general population ranges from .08 percent to .2 percent, is more common in women than men and increases with age, Michalek noted. The incidence of diabetes differs depending on ethnicity, ranging from 6 percent among non-Hispanic whites, 7.7 percent among Hispanics, 9 percent among African Americans, and about 18 percent among Native Americans. However, the incidence among the Puma Indians of Arizona reaches approximately 70 percent in those between the ages of 55 and 64, Michalek said.

"Our findings support the need for further investigation of the association between diabetes and hypothyroidism in American-Indian populations, particularly among those with known high rates of diabetes," he said.

"The ability to diagnose and treat unsuspected hypothyroidism in these populations could greatly enhance quality of life."

Also participating in the study were Martin C. Mahoney. M.D., Ph.D., UB assistant professor of family medicine and director of screening services at RPCI, and Donald Calebaugh, M.D., director of the Pleasant Point Health Center in Eastport, Maine.