Atherosclerosis is the world's leading cause of death 1. Much, but not all, is known about atherosclerosis development. Classical modifiable risk factors include diabetes mellitus, hypertension, hyperlipidemia, and smoking, while other important risk factors include abdominal obesity, excessive alcohol intake, lack of fruit and vegetable intake, and psychosocial factors 2. The suggestion that thyroid function may be related to atherosclerosis is not new 3. There is general agreement that overt hypothyroidism promotes cardiovascular disease, including atherosclerosis. Mechanisms through which decreased thyroid hormone concentrations lead to atherosclerosis include elevated low-density lipoprotein cholesterol, diastolic hypertension, heightened coagulability, and actions on vascular smooth muscle 3. However, much debate continues whether subclinical hypothyroidism similarly leads to increased cardiovascular events. A very large meta-analysis of previous studies suggested modestly increased risk with subclinical hypothyroidism 4, although there was significant heterogeneity of the results among the studies included. The meta-analysis also found that by age, the youngest patients had the most positive hazard ratio estimate, but statistical significance was not reached, likely because of small subgroup numbers 4. Interestingly, a recent paper reported increased cardiovascular events in younger (70 years) patients with subclinical hypothyroidism 5. This is interesting because subclinical hypothyroidism in some older individuals may not be pathologic, and is less likely to be due to autoimmune thyroid disease 6.
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