Subclinical hypothyroidism and hyperthyroidism may be associated with a modest increased risk for coronary heart disease (CHD) and mortality, with lower risk estimates when pooling higher-quality studies and larger confidence intervals (CIs) for subclinical hyperthyroidism, according to the June 3 issue of the Annals of Internal Medicine.
Nicolas Ochs, MD, from the department of ambulatory care and community medicine at the University of Lausanne in Lausanne, Switzerland, and colleagues undertook the study to summarize prospective evidence about the relationship between subclinical thyroid dysfunction and CHD and mortality due to previous conflicting data.
Two reviewers screened and selected cohort studies from MEDLINE (1950 to January 2008) that measured thyroid function and then followed persons prospectively to assess CHD or mortality. By using a standardized protocol and forms, two reviewers independently abstracted and assessed studies.
The researchers identified 10 of 12 studies that involved population-based cohorts that included 14,449 participants. All 10 population-based cohort studies examined risks associated with subclinical hypothyroidism (2,134 CHD events and 2,822 deaths), whereas only five examined risks associated with subclinical hyperthyroidism (1,392 CHD events and 1,993 deaths), according to the investigators.
In a random-effects model, the authors wrote that relative risk (RR) for subclinical hypothyroidism for CHD was 1.20 (95 percent, CI).
Risk estimates were lower when higher-quality studies were pooled (RR, 1.02 to 1.08) and were higher among participants younger than 65 years (RR, 1.51 for studies with mean participant age older than 65 years and 1.05 for studies with mean participant age ≥65 years), Ochs and colleagues reported.
The authors wrote that RR was 1.18 for cardiovascular mortality and 1.12 for total mortality. For subclinical hyperthyroidism, the researchers found that RR was 1.21 for CHD, 1.19 for cardiovascular mortality and 1.12 for total mortality.
To note their limitations, the investigators wrote that individual studies were adjusted for different potential confounders and one study provided only unadjusted data. They also said that “publication bias or selective reporting of outcomes could not be excluded.”
The researchers concluded that the data were uncertain. CIs around risk estimates were wide, particularly for those related to subclinical hyperthyroidism, according to the investigators.
The authors noted that higher-quality studies showed lower estimates of risk than lower-quality studies.
As a result of their uncertain findings, Ochs and colleagues stressed that randomized trials testing the efficacy of thyroxine replacement and antithyroid medications for subclinical hypothyroidism and subclinical hyperthyroidism are needed.