Is “natural” thyroid hormone better?

Hypothyroidism is a common disorder effecting over 10 million Americans. It occurs when the thyroid gland loses its ability to produce an adequate amount of hormone to meet the body’s needs. Hypothyroidism is treated by replacing the thyroid hormone in pill form.

Desiccated thyroid hormone (DTH) has been commercially available since 1934. It is made by extracting thyroid hormone from the thyroid glands of pigs and cows. Because it comes from animals, it is referred to as being “natural.”

Synthetic thyroid hormone (levothyroxine – T4 and Liothyronine – T3), is produced by pharmaceutical companies. These have been available since the early 1960s. While they are made using chemical reactions, they are atom-for-atom the same as the hormone your body makes and the hormone taken from animal sources. Synthetic is not “artificial.” Levothyroxine and Liothyronine are not chemical compounds that mimics thyroid hormones, they ARE thyroid hormones.

Is “natural” thyroid hormone better than “synthetic” thyroid hormone? No. There are three problems with DTH. First, because every thyroid gland contains different amounts of thyroid hormone, it is difficult to manufacture a consistent product. DTH producers have been shut down by the FDA on several occasions because the variance between batches of medication was considered to be too great. A person using DTH can get pills labeled as continuing the same dose of thyroid but actually receive highly varying amounts. Synthetic hormones do not have this problem.

Second the ratio of T4 and T3 (the active forms of thyroid hormone in the blood) differs between humans and the animal sources of the DTH. In humans there is 1 molecule of T3 for every 14 molecules of T4. In pigs and cows there is 1 molecule of T3 for every 4 molecules of T4. So in humans T3 is 7% of the thyroid hormone produced whereas in DTH it is 20%. The higher percentage of T3 may lead to symptoms of excess thyroid hormone in patients. Levothyroxine is the T4 form of thyroid hormone. Your body converts the T4 into T3 as it needs it. Therefore you are not at risk of excess T3 effects on the body.

Finally, the ratio between the T4 and T3 in DTH is constant. Therefore increasing the dose of DTH raises both T4 and T3. Likewise, decreasing the dose will decrease both T4 and T3. Synthetic T4 (levothyroxine) and T3 (liothyronine) may be dosed separately allowing your provider to customize the amount you receive.

Because it contains both T4 and T3, patients often feel better on DTH than typical synthetic hormone replacement. This is because many providers who use synthetic hormone only give the T4 form of the hormone. If you do not feel well on the levothyroxine alone, ask your provider about using both T4 and T3 or see an endocrinologist trained in the use of both forms of the hormone.

Use of synthetic thyroid hormone can provide consistent relief from the symptoms of hypothyroidism. It provides your body with the exact hormones that it has lost the ability to make.

Dr. Samuel Abbate is a local physician practicing in Wasilla at the Alaska Diabetes and Endocrinology Center.