Jennifer Warner, Everyday Health
Thyroid Nation


Jennifer shares how cold weather can effect your thyroid.


Cold winter weather may make it more likely that you’ll be misdiagnosed with a mild case of hypothyroidism even though your thyroid is actually healthy.

Mild hypothyroidism, also known as subclinical hypothyroidism, happens when your thyroid function becomes slightly impaired and the thyroid gland is unable to produce enough thyroid hormone to meet your body’s needs.

A 2013 study suggests that natural seasonal variations in hormone levels may cause some doctors to mistakenly diagnose people with subclinical hypothyroidism.

It potentially could lead to overdiagnosis of hypothyroidism if the doctor is not aware of what is going on with the seasons,

says David S. Cooper, MD, a professor of medicine in the division of endocrinology, diabetes, and metabolism at the Johns Hopkins University School of Medicine in Baltimore, who is not affiliated with the study.

Understanding Subclinical Hypothyroidism

Slightly elevated thyroid-stimulating hormone (TSH) levels are a hallmark of subclinical hypothyroidism, Dr. Cooper says. TSH is produced by the pituitary gland and regulates thyroid function. When thyroid function is impaired, TSH levels increase to compensate.

Subclinical hypothyroidism is typically diagnosed when thyroid hormone (such as free thyroxine, or T4) levels are normal but TSH levels are slightly higher than normal and there are no other symptoms of hypothyroidism, like fatigue or weight gain. (Blood tests are used to measure these hormone levels.)

In most cases, subclinical hypothyroidism is an early stage of hypothyroidism and is treated with hormones to help keep it from progressing and causing complications. In other cases, the condition may resolve or remain unchanged without treatment.

Experts say people who have elevated TSH levels despite having normal thyroid hormone levels should be considered for treatment.

RELATED: What Women Need to Know About Thyroid Disorders

Seasonal Changes and Thyroid Function

The 2013 study, in the Journal of Clinical Endocrinology & Metabolism, suggests that seasonal variations in TSH levels should be taken into account before making a diagnosis of subclinical hypothyroidism.

The researchers measured TSH levels every month in 1,751 people with subclinical hypothyroidism and 28,096 healthy people with normal thyroid function. The results showed a significant seasonal pattern in TSH levels. TSH increased in the cold winter-to-spring months and decreased in the summer and fall in both healthy people and those with subclinical hypothyroidism.

People with subclinical hypothyroidism were nearly 1.5 times more likely to revert to normal TSH levels during warm weather. Similarly, people with normal thyroid function were more likely to be diagnosed with subclinical hypothyroidism because of elevated TSH levels in the colder months.

“It’s actually a really interesting study,” Cooper explains.

Other studies have also noticed that there may be a flux in thyroid function seasonally. It’s as if the body is trying to cope or compensate for the cold by increasing hormone levels to generate more heat. It’s not that winter is affecting the thyroid – more that winter is making TSH slightly higher.

The practical message of the study, Cooper says, is that people should be tested for thyroid problems more than once at different times of the year before starting on treatment.

“It’s not appropriate to base potentially lifelong treatment on a single blood test,” he notes.

**This article originally featured on EverydayHealth.com**


Reviewed by Farrokh Sohrabi, MD

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