Inositol has far-reaching effects upon hormones, because of its position as one of three major classes of second messengers in cells.
Think of second messengers as the second string of relay runners: the first runner hands off the baton and the second messenger takes it from there, carrying the signal to the end target as well as amplifying the signal itself. We usually think of hormones as effecting their purpose all on their own, but in reality, it’s the second messengers that do their dirty work. If levels of these are low, then the hormones cannot perform their functions as they should, and resistance to the hormone’s signal begins to develop. (The other two primary categories of second messengers are cyclic nucleotides, cAMP and cGMP, and calcium ions, which can play a huge role in excitotoxicity and various kinds of sensitivities such as EMF).
Those hormonal processes that seem to use inositol (and diacylglycerol or DAG, related in the reaction necessary to produce the usable form of inositol) include TSH, vasopressin, angiotensin, GABA, serotonin, insulin, and the pituitary hormones LH and FSH. (The downstream effects of both inositol and DAG also recruit calcium).
Fertility: LH and FSH
Inositol is a common treatment for PCOS (Polycystic Ovarian Syndrome) for several reasons. First, it seems that its effects upon regulating insulin help to lower LH secretion.
Second, the signal from the hypothalamus that triggers release of LH and FSH from the pituitary is Gonadotropin-releasing hormone (GnRH), and it uses inositol as a second messenger. While the pituitary is its primary target, ovarian follicles also contain GnRH receptors—so its signal can have a direct regulating effect upon them.
Even in women who do not have PCOS, inositol appears to support quality oocytes and follicular maturity.
Inositol seems to support fertility in men, as well. The pituitary FSH signals the Sertoli (sperm-producing) cells, which respond with inositol as their second messenger, which then assists with motility of sperm, as well as the processes called capacitation and acrosome reactions necessary for fusion of the sperm with the oocyte. It also seems to increase sperm count and concentration, and to rebalance LH and FSH, as well as inhibit B, a hormone that acts like a see-saw with FSH.
Since inositol has such profound effects upon LH and FSH, both produced by the pituitary, it’s not surprising that it also acts as a second messenger TSH, or Thyroid Stimulating Hormone. This is the hormone most frequently tested in monitoring hypothyroidism. Inositol has thus been found to help regulate TSH levels in much the same way that it helps to regulate FSH and LH levels.
Metabolic Syndrome: Insulin, Cholesterol, and Blood Pressure
Inositol also acts as a second messenger for insulin, the hormone necessary to allow glucose inside the cells. It thus assists with insulin sensitivity. Probably because of this at least in part, it helps with many other markers of metabolic syndrome, including improvement in blood pressure, triglyceride and cholesterol levels.
Depression and Anxiety: Serotonin and GABA
Inositol has long been used for anxiety due to its effects as a second messenger for serotonin as well. It thus helps to sensitize cells to serotonin’s mood-boosting signals. It also boosts the calming neurotransmitter GABA’s signals as well.
To the extent that low inositol is to blame for insensitivity to the above hormones, I suspect that poor diet is often the culprit. Food sources of inositol include many whole foods, such as soy, chickpeas, brown rice, wheat germ, lentils, barley, oats, buckwheat, beef, oranges, grapefruit, strawberries, peas, and cauliflower.
Soy lecithin contains more than double the amount of inositol as chickpeas, the next highest source—and since soy is often avoided for various reasons, this may be a small part of the problem. While I think soy has an undeserved reputation for the most part, one concern I do have with soy is that it is usually genetically modified unless specifically labeled as non-GMO or organic. If it contains either of these labels, I rarely recommend avoidance of soy except for when iodine is overtly low (until we correct the problem) or if someone has a food sensitivity to soy, as that’s a common one. Even then, most people with soy sensitivities can tolerate soy lecithin (as it is a fat, and food sensitivities are generally to the protein).
That said, the other foods on the list, if eaten in quantity, can compensate for soy avoidance. Inositol powder can also be taken as a supplement.