Subclinical thyroid dysfunction and quality of life : Longterm outcome for older people with stable cardiovascular disease

Cardiovascular disease (CVD) and subclinical thyroid dysfunction are common among older populations. As life expectancy has steadily grown with the proportion of those over 65 expected to further increase in the future, worldwide, a greater burden of CVD and subclinical thyroid dysfunction will occur. Notwithstanding this, older individuals have traditionally been inadequately represented in cardiovascular trials. Knowledge on health-related quality of life (HRQoL) and its long-term effect regarding stable CVD, alongside factors predicting HRQoL is scarce. Furthermore, the long-term outcome of subclinical thyroid dysfunction and levothyroxine substitution among this population upon prognosis and their HRQoL is unclear. In this thesis, we aimed to gain knowledge on the effects of stable CVD in older individuals related to subclinical thyroid dysfunction upon their mortality, cognition, and HRQoL. Of special interest was also HRQoL in relation to stable CVD compared to that of the general population alongside predictors of impaired HRQoL. In these studies, stable CVD we defined as having one or more of the following: prior myocardial infarction, coronary artery disease, previous stroke, transient ischemic attack, or peripheral artery disease. This thesis is based on secondary analyses of the prospective, real-life-based Drugs and Evidence Based Medicine in the Elderly (DEBATE) study that was originally aimed at assessing multifactorial cardiovascular prevention. Primarily comprising 400 home-dwelling individuals over age 75 with stable CVD, their clinical and laboratory examinations took place annually from 2000, with their thyroid-stimulating hormone (TSH) tests taking place in 2002. Cognitive performance and severity of cognitive disorder was assessed with the Consortium to Establish a Registry for Alzheimer’s Disease neuropsychological battery (CERAD-nb) and the Clinical Dementia Rating (CDR) scale, with screening of depressive syndromes measured with the Zung Self-Rating Depression Scale (Zung SDS). The 15D tool served for assessing HRQoL. Comparison of HRQoL between older people with stable CVD and the general population required, an age- and gender-matched control population from the Finnish National Health 2000 Health Examination Survey (Health 2000 Survey). Data on mortality we retrieved from Statistics Finland. In these studies, among individuals over 75 with stable CVD, TSH affected neither 10-year total mortality nor 5-year cardiovascular mortality. Elevated TSH concentrations did not associate with deteriorated cognitive performance, however, higher TSH concentrations associated with better CDR scores. Moreover, whereas TSH did not influence HRQoL, levothyroxine treatment had a negative impact on the HRQoL of older people with stable CVD. Stable CVD causes deterioration in the HRQoL of older individuals compared to the HRQoL of the age- and gender-matched general population with predictors of impaired HRQoL including Mini-Mental state examination (MMSE), number of medications, BMI, and age. Furthermore, among older people with prior CVD, subclinical thyroid dysfunction does not associate with mortality, cognitive performance, or HRQoL. However, elevated TSH levels associate with significantly better CDR scores. Finally, as levothyroxine substitution lowers the HRQoL of these individuals, the possible treatment of persistent subclinical hypothyroidism should be carefully and individually tailored regarding such factors as level of elevated TSH, age, comorbidities, and medications.