DOCTOR'S PAGE, Thyroid gland

The impact of obesity on thyroid gland

სტატია ექიმებისთვის

Connection between thyroid gland and obesity became more clear during last years.

More specifically, when isolated elevation of TSH (<10) presents in obese individuals, this change may be the consequence of obesity and not vice versa.

In fact, the treatment of hypothyroidism cause only mild (less then 10%) decrease of body weight. It may mean that obesity isn't always the secondary state and hormonal changes might be compensatory process in response to obesity.

The attention must be paid to other hormone levels besides TSH for differentiation. If the autoimmune markers are elevated, if the thyroid hormone levels are low and symptoms of hypothyroidism are presented it really points that thyroid dysfunction is the primary disorder.

Most individuals with obesity don't experience any structural or functional changes of thyroid gland.

In other cases these types of changes are observed: weight loss causes decreasing of TSH and FT3 and weight gain conversely elevates the levels of these hormones.

When obesity is the primary disorder, FT4 level usually is normal or upper normal. This fact differentiates obesity related hyperthyrotropinemia from the true subclinical hypothyroidism, which is mostly characterized by low normal FT4 levels.

Besides high risk of hypothyroidism, obesity can also lead other types of thyroid gland damage.

According to studies obesity increases risks of autoimmune thyroid disease, particularly in children and is manifested by elevation of thyroid antibodies (Anti-TPO and Anti-TG).

Structural changes may also be observed on thyroid ultrasound, Specifically, diffusely reduced echogenicity and enlargement of the gland may be presented. These changes are also characteristic for Hashimoto's thyroiditis. So autoimmune disorder mustn't be diagnosed just by ultrasound findings and autoimmune markers must also be assessed in order to avoid diagnostic mistakes.

The elevation of TSH causes the activation and enlargement of thyrocytes, which can lead not only growth of the whole gland, but also increases risks for developing thyroid nodules including malignant lesions too.

Treatment

Hyperthyrotropinemia due to obesity is transient and alleviates after weight loss.

Even moderate increase in physical activity, without changes in BMI, causes lowering of TSH and FT4 levels. Ultrasound abnormalities can also normalize.

According to some recommendations this state doesn't need to be treated with the replacement therapy. But here me must also consider the risks related with high TSH including changes in gland structure which can lead to malignancy, particularly in case if weight loss won't be achieved.

Moreover, if the differential diagnosis mistakes and a "true" hypothyroidism coincides with obesity, it can even more increase the risks of cardiovascular disease and other metabolic abnormalities related with obesity.

Hypothyroidism also alters lipid metabolism and it promotes vascular damage in this regard too.

And the last thing is that hypothyroidism can become a reason of failure in events aimed at weight loss.

So while the assessment and treatment of hypothyroidism are both easy and safe, it's better for patients with obesity to assess and treat hypothyroidism routinely.

As conclusion, the hormonal imbalance must be treated properly, although every patient should be informed that this intervention alone can't be enough to achieve desired level of weight loss and the effect in this regard will be mild. Particularly in case when obesity is the leading disorder, not the result of underactive thyroid.

Written by: Elga Giorgadze, MD