The background of the study. Subclinical hypothyroidism is common, as is diabetes mellitus. This study was done to determine the frequency of subclinical hypothyroidism, the likelihood of its progression, and its relationship to cardiovascular disease in women with type 2 diabetes.
How the study was done. The study subjects were 420 women with type 2 diabetes who were participants in a prospective, community-based study, the Fremantle (Australia) Diabetes Study. The women were evaluated annually for 5 years. Subclinical hypothyroidism was defined as a high serum thyrotropin (TSH) concentration (>5.1 mU/L) and a normal serum free thyroxine concentration in a woman with no history of thyroid disorder.
The results of the study. At base line, the mean age of the 382 women was 64 years, the mean duration of diabetes was 4 years, and the mean body-mass index was 30 kg/m2. Thirty-three women (9 percent) had a high serum TSH concentration, and 7 women (2 percent) had a low concentration; all had normal serum free thyroxine concentrations. Serum concentrations of cholesterol and other lipids were similar in the women in the three serum TSH groups. There was no association between subclinical hypothyroidism at base line and blood pressure, coronary heart disease, cardiac failure, body-mass index, or metformin or insulin therapy at base line or follow-up.
At five years, 111 women (29 percent) returned for reevaluation. Nine women (8 percent) had a high serum TSH concentration and none had a low concentration. The values were high at both times in 3 women, high only at base line in 4 women, and high only at five years in 6 women.
The conclusions of the study. Some women with type 2 diabetes have subclinical hypothyroidism, but it is not a risk factor for lipid disorders, hypertension, or cardiovascular disease, and progression to more severe hypothyroidism is rare.
The original article. Chubb SA, Davis WA, Inman Z, Davis TM. Prevalence and progression of subclinical hypothyroidism in women with type 2 diabetes: the Fremantle Diabetes Study. Clin Endocrinol (Oxf) 2005;62:480-6.