TEMPERATURE-DEPRESSION THYROID LINK?

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Is there a relationship between basal body temperatures, depression, and thyroid disorders? A 52-year-old man, who had previously monitored his first morning temperatures on occasion, recently followed them for 20 days. On a few occasions, his temperature was <97.0°F, although he felt comfortable. Recently, he has been comfortable at a consistent temperature of 97.4°F. In the past four months, he has taken to sleeping in sweatpants, flannel shirt, and a hooded sweatshirt with the hood up, while others in the house sleep in their usual light clothing. Last fall, his thyroid stimulating hormone (TSH) was 2µU/mL; he has no other symptoms of underactive thyroid. His overall health and lab studies are normal. For many years, he has had a social anxiety disorder and depression.
—Greg Goetz, MD, Hales Corners, Wis.

The clinical signs and symptoms of hypothyroidism are myriad and oftentimes nonspecific. Classically, we are taught that an underactive thyroid leads to a general “slowing” of metabolic processes, resulting in many of the associated symptoms: cold intolerance, weight gain, depression, hyperlipidemia, and neurocognitive deficits (among many others). Some of these have been well studied. The link, for example, between hypothyroidism and cold intolerance is well understood. In normal circumstances, thyroid activity increases in response to a cold stress at the hormonal urgings of the hypothalamus. This increased thyroid activity leads to metabolic heat production as well as shivering to raise body temperature. In the context of an underactive thyroid, basal metabolic (“obligatory”) heat production is decreased as is the adaptive response to cold exposure. Peripheral vasoconstriction also occurs, leading to the subjective sensation of cold intolerance and even hypothermia in certain situations (Ann Intern Med. 2003;139:205-213). The link between depression and hypothyroidism, despite classic teaching, may be less well understood. One study of 160 subjects showed that in the 76 with overt or subclinical hypothyroidism, quality-of-life ratings were lower and anxiety and depression ratings were higher compared with normal subjects (Arch Med Res. 2006;37:133-139). A Norwegian study using a large database (>30,000 patients, mostly middle-aged to elderly) did not find an increased risk of depression or anxiety among hypothyroid patients (Acta Psychiatr Scand. 2002;106:27-34). Your patient’s TSH level is within normal limits, making it unlikely that hypothyroidism is playing a role in his mildly reduced temperatures or mood disturbance.
—Christopher Ruser, MD (100-8)

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