How Changes in Season and Temperature Affect Thyroid Function

Changing leaves

Many thyroid patients expect to feel more hypothyroid symptoms in colder weather. Such symptoms like fatigue, constipation, hair loss, and dry skin—that may be well-managed during warmer months—return or worsen when it’s cold outside. Moreover, people with hypothyroidism regularly report increased weight gain (or greater difficulty losing weight) during colder months, too.

As a response, some patients and practitioners plan ahead, scheduling an increase in the dosage of thyroid hormone replacement medication as cooler temperatures approach. Similarly, as warmer weather begins, they may plan a decrease in the dosage of thyroid medication to maintain stable thyroid function and effectively manage symptoms.

What the Research Tells Us

Recent research published in Thyroid confirms there are seasonal variations in thyroid function and thyroid levels. And, in turn, this may have a significant impact on hypothyroidism treatment effectiveness.

The study, conducted at Ben Gurion University in Israel, examined roughly 250,000 thyroid stimulating hormone (TSH) test readings from over 40,000 people with hypothyroidism. This was compared to 2.2 million TSH test readings from about 900,000 people with normal thyroid function.

The evaluation was conducted between January 2013 and March 2017 and the research found some interesting results:

  • Sixteen to 33 percent of women studied had TSH levels above the reference range and nine to 17 percent had levels below the reference range on average each month.
  • Twenty-three to 43 percent of men had levels above the reference range and seven to 23 percent had levels below the reference range on average each month.
  • The monthly TSH level results were significantly higher during winter months (November through February) compared to summer months (June through September) for men and women, whether they were hypothyroid or had normal thyroid function.
  • Women, in general, had a significantly larger increase in TSH levels in winter and a smaller drop in TSH levels in the summer, compared to the men studied.
  • In men over 65, however, the amount of them who were above the reference range was significantly higher in winter versus summer.

Of greatest significance to people with hypothyroidism, the researchers also found that a significant percentage of the hypothyroid patients observed were being sub-optimally treated.

More specifically, a higher percentage of the people studied who were being treated for hypothyroidism had TSH levels above the reference range throughout the year. And, the TSH levels of the study members who were hypothyroid also increased more in the winter than the group with normal thyroid function.

What This Means for Thyroid Patients

The thyroid attempts to maintain homeostasis (balance) in terms of thyroid hormone production, no matter what external factors affect it. Similarly, the body aims to maintain an internal temperature around 98.6 degrees Fahrenheit, despite the temperature outside.

But, the thyroid is sensitive to changes in temperature. It ramps production of hormone up and down in response to significant temperature changes or chronic exposure to hot or cold temperatures.

In particular, research shows that colder seasons and climates—or chronic exposure to cold temperatures—can lower levels of thyroid hormones and increase TSH levels. Similarly, warmer seasons and climates—or chronic exposure to hot temperatures—can increase levels of thyroid hormones and decrease TSH levels.

A Word From Verywell

For people with hypothyroidism, a cold weather-induced increase in TSH levels can be accompanied by a worsening of hypothyroidism symptoms. The effects of cold weather may, however, be avoidable with adjustments to dosages of thyroid hormone replacement medication.

If you live in an area with cold winters, are moving to a colder climate, or anticipate an extended period in an area with colder-than-usual temperatures, consider discussing your thyroid treatment level with your healthcare provider.

To start, you may want to schedule a complete thyroid test panel prior to the onset of or move to colder temperatures. This will establish your baseline levels. Then, have these levels re-checked six to eight weeks after the onset of cold temperatures. This will determine if you need an adjustment to your dosage of thyroid hormone replacement medication.

If you do increase your dosage in response to colder temperatures, don’t forget to plan ahead with your practitioner. Re-check your levels and/or schedule a dosage decrease when warmer weather returns or when you return to a warmer climate area.

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Article Sources
  • Arbelle, J.E. et al. “Circannual Variability of Thyroid Axis Function Based Upon TSH Results from Hypothyroid-Treated and Healthy Individuals Over Time.” Thyroid. October 2017, 27(S1): A-166-A-188. 
  • Hoermann, R. et. al. "Homeostatic Control of the Thyroid–Pituitary Axis: Perspectives for Diagnosis and Treatment." Front Endocrinol. 2015; 6: 177.
  • Maslov, LN, et. al. "Role of thyroid system in adaptation to cold." Ross Fiziol Zh Im I M Sechenova. 2014 Jun;100(6):670-83.