Subclinical Thyroid Dysfunction and Risk of Myocardial Infarction and Stroke
Condition: Cardiovascular Diseases; Heart Diseases; Hypothyroidism; Myocardial Infarction; Cerebrovascular Accident
MeSH terms: Stroke; Cardiovascular Diseases; Heart Diseases; Myocardial Infarction; Hypothyroidism; Infarction
Study type: Observational

Summary: 
      To examine the association of subclinical hypothyroidism and risk of myocardial infarction
      and stroke in a large prospective cohort of post-menopausal women.
    

Detailed description: 
      BACKGROUND:

      Cardiovascular disease, including myocardial infarction (MI) and stroke, is the leading cause
      of death for women in the United States. Subclinical hypothyroidism (SCH), in which thyroid
      hormone levels are in the normal range but thyroid stimulating hormone (TSH) is elevated, has
      been linked to abnormal lipid profiles, atherosclerosis, and MI. The literature is scant
      however, and the evidence constrained by small studies, many of cross-sectional design. Both
      the US Preventive Services Task Force and the Institute of Medicine recently concluded that
      current data are insufficient to inform clinical decision-making about the need for screening
      or treatment for SCH.

      DESIGN NARRATIVE:

      This is a case-cohort study within the 93,676-member Observational Study of the Women's
      Health Initiative, including 800 women who have experienced an MI, 750 with
      thrombotic/embolic stroke, and a randomly selected subcohort of 3,200 women density-matched
      for age, race/ethnicity, and clinical center. Participants have extensive baseline
      demographic, health, behavioral, and physical exam data and stored serum available. The
      investigators will measure TSH and thyroid hormone levels in order to identify SCH at entry.
      Follow-up includes annual health status updates and a physical exam in the third year; >=5
      years have passed since enrollment for all women. Thus, using new laboratory studies and
      existing Women's Health Initiative (WHI) data, they will be able to answer these primary
      research questions: Among women without a history of thyroid disease, MI, or stroke: 1) Is
      subclinical hypothyroidism at baseline independently associated with risk of MI? 2) Is
      subclinical hypothyroidism at baseline independently associated with risk of ischemic stroke?
      3) What form of association best describes the relationship between TSH, as a continuous
      measure, and risk of MI and stroke? 4) What are the population correlates (i.e.,
      race/ethnicity, body mass index (BMI), hormone therapy, comorbidity) of SCH? This information
      - currently unavailable for middle-aged and older women - is germane to public health and
      health care policy to define the burden of illness associated with SCH, and to quantify the
      benefits and costs of eventual population screening and treatment
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Postmenopausal women aged 50-79 years, who enrolled in the Women's Health Initiative (WHI)
        Observational Study (n=93,676). Participants include African American, Asian,
        Hispanic/Latino and European-American individuals recruited from the communities
        surrounding the WHI study centers..