Inositol is a molecule found in most cells in the human body and is critical to many aspects of human health. It is part of the structure of cellular membranes, and it is also important for lipid transport and many signaling pathways. Inositol is closely related to B vitamins and is sometimes referred to as vitamin B8.

Inositol and its derivatives have been shown to support the structure and proliferation of cells and the signaling of many molecules including the thyroid-stimulating hormone (TSH). In research, the altered metabolism of inositol has been shown to impact the biosynthesis, storage, and secretion of thyroid hormones. When compared to healthy individuals, metabolomic demand for inositol was shown to be increased in individuals diagnosed with hypothyroidism.

The most common form of inositol is myo-inositol, a molecule that has been shown to support many aspects of metabolic health. It can be found in fruits, nuts, beans, and certain grains. Myo-inositol has been shown in studies to support thyroid function and a normal immune response. Serum thyroid-stimulating hormone (TSH) levels and intracellular myo-inositol concentrations have been correlated in laboratory studies. Thyroid cells have been shown to accumulate myo-inositol concurrent with the increase of TSH levels. 

During the production of thyroid hormones, myo-inositol acts as a second messenger in the phospholipase C-dependent inositol phosphate calcium/diacylglycerol pathway. This pathway is critical to the generation of the hydrogen peroxide used in thyroid hormone biosynthesis and iodine organification. Myo-inositol is also a precursor to many molecules involved in signal transduction pathways related to certain hormones including TSH.

The synergistic effects between myo-inositol and selenium, an element with thyroid-supportive properties, have been researched in clinical studies. A randomized trial explored the efficacy of supplementation with 83 μg of selenium (Se) as compared to 600 mg of myo-inositol plus 83 μg of selenium (myo-inositol + Se). The trial involved 48 participants with autoimmune-related subclinical hypothyroidism randomized to either the myo-inositol + Se group or the Se group for 6 months.

After the treatment period, the myo-inositol + Se group experienced a 31% decrease in TSH, 44% decrease in thyroid peroxidase antibody (TPOAb), and 31% decrease in thyroglobulin antibodies (TgAb). Although the Se-only group showed improvements in their levels of thyroid antibodies, no change in TSH levels was observed. A similar study with the same treatment levels of myo-inositol + Se reported significant improvements in TSH and quality of life.

A clinical study involving 168 individuals with hypothyroidism reported improvements in TSH, TPOAb, TgAb, and free T4 (fT4) in the myo-inositol + Se group as compared to Se alone. A study involving pregnant individuals with a TSH between 1.6 and 2.5 μIU/mL explored the efficacy of daily supplementation with myo-inositol + Se from the first through the third trimesters. The study results showed a stabilization of TSH, fT4, and free T3, and the authors reported increased prevention of subclinical hypothyroidism.

Myo-inositol is a compound with many health-supportive qualities. It may support healthy metabolism, ovarian health, and a healthy mood. Recent research also indicates that it may support thyroid function and thyroid hormone signaling. 

By Colleen Ambrose, ND, MAT