CONTEXT: Subclinical hypothyroidism (SCH) is a common condition that has been associated with ischemic heart disease (IHD) in some, but not all, studies. This may be due to differences in study design and the characteristics of participants. OBJECTIVE: Our objective was to investigate whether age and gender influence IHD prevalence, incidence, and mortality in people with SCH. DATA SOURCES: Computerized (PubMed, EMBASE, and Cochrane Library) and manual searches of the literature to May 2007, published in English, were performed. STUDY SELECTION: Epidemiological studies that quantified thyroid status and IHD events in adults were performed. DATA EXTRACTION: Two authors independently reviewed articles and abstracted data. Results were compared across two groups based on the minimum age of participants studied (younger than 65 yr and 65 yr or older). DATA SYNTHESIS: There were 15 studies included for analysis with 2,531 SCH participants and 26,491 euthyroid individuals. IHD incidence and prevalence were higher in SCH subjects compared with euthyroid participants from studies including those younger than 65 yr, but not studies of subjects aged older than 65 yr [odds ratio (95% confidence interval)]: 1.57 (1.19-2.06) vs. 1.01 (0.87-1.18) and 1.68 (1.27-2.23) vs. 1.02 (0.85-1.22), respectively. Cardiovascular/all-cause mortality was also elevated in participants from the younger than 65-yr studies, but not from the studies of older people: odds ratio 1.37 (1.04-1.79) vs. 0.85 (0.56-1.29). Prevalent IHD was higher in SCH participants of both genders, although this was statistically significant only in women. CONCLUSIONS: SCH is associated with increased IHD (both prevalence and incidence) and cardiovascular mortality only in subjects from younger populations. These data suggest that increased vascular risk may only be present in younger individuals with SCH.
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