Seasonal Changes in Thyroid Levels

For years we've known that some patients benefit from a slight increase in thyroid medication dosage during colder months. But that's been considered “patient-based evidence,” and not formal research findings, so it’s often disregarded.

Now, researchers at the American Thyroid Association 2021 annual meeting reported on specific seasonal changes in thyroid levels, and their findings may have an impact on how you treat your hypothyroidism.

Their study looked at more than 6,000 people, and found that:

• TSH levels increased in Winter, with the highest levels seen in January, and high levels in Winter and Spring

• TSH levels decreased in Summer, with the lowest levels in May and June

• Free T3 levels were highest in Summer, and lowest in Winter

Bottom Line: This research provides further evidence that a slight dosage increase as the weather gets colder may help you better manage your hypothyroidism to maintain optimal levels. And if you take T3 (i.e., generic liothyronine or Cytomel) in combination with other thyroid medication, you may want to discuss with your doctor whether it makes sense to slightly increase the T3 dosage during winter months as well.

Source: Yamada, Sayaka et. al. "Variations in Thyroid Function in Over 6,000 Healthy Subjects in Japan," American Thyroid Association Annual Meeting Clinical Poster, October 2021, Poster 231, https://www.liebertpub.com/doi/full/10.1089/thy.2021.29115.abstracts