The supplement inositol is a superstar for treating polycystic ovary syndrome. It’s also been clinically trialled for weight loss, thyroid disease, anxiety, insomnia, and premenstrual mood symptoms.
In this episode, Lara looks at:
One thing Lara forgot to mention is that to get results with inositol, you need to commit to it for at least three months. And if it works, you’ll probably want to stay on it for years. Luckily, inositol can be quite inexpensive, especially if you choose straight myo-inositol powder.
The supplement inositol is a superstar for treating polycystic ovary syndrome. It’s also been clinically trialled for weight loss, thyroid disease, anxiety, insomnia, and even premenstrual mood symptoms. One of the questions I get a lot is “which is better: Myo-inositol or D-chiro-inositol?” And today we’re going to look at the science on that plus lots of other information about inositol.
Welcome back to the podcast. I’m your host Lara Briden, a naturopathic doctor and author of the books Period Repair Manual and Hormone Repair Manual. After a lovely couple of months visiting my family in Canada, I’m back in Christchurch, New Zealand where I live and see patients. And I’m realizing that it’s been more than two months since my last episode, for which I apologize. But I am committed to bringing you new content, so let’s get into it.
As promised, today is all about the supplement myo-inositol, which is often labelled as just “inositol.” Inositol is one of the most evidence-based supplements for PCOS. It can also help with weight loss, thyroid, anxiety and sleep, which we’ll touch on today. And inositol is—dare I say it—a little enigmatic and hard to explain.
Starting with, what is inositol? Well, inositols are small molecules that are structurally similar to glucose, also called carbocyclic sugars, sugar alcohols, or cyclic polyols. And you’ll notice that I’m saying inositols—plural—because there are different types. And if you’re thinking that inositol being a sugar sounds bad because sugar is unhealthy, please don’t worry! Lots of kinds of sugars including inositols are a normal and integral part of our body chemistry.
Next, where do we get inositol? In short, we make it. For example, each kidney makes about two grams per day and the liver and brain also make quite a lot. In fact, the level of inositol in the brain is higher than in any other tissue and all that brain inositol is quite important for the healthy functioning of neurotransmitters such as dopamine, acetylcholine, GABA, and serotonin. Which is why inositol supplements have been clinically trialled for anxiety, depression, premenstrual mood disorders, and insomnia. I’ve personally been trying inositol for my menopausal sleep problems, taking three grams at night together with the amino acid glycine. And I think it’s helping.
So, yes. In addition to being made by the body, inositol can be consumed, either as a supplement, which is the topic of today or from food. An average modern diet delivers about 700 mg of inositol mostly as inositol hexaphosphate or phytate from grains and seeds. Interestingly, some scientists propose that much of the benefit from dietary fibre may actually be from its phytate or inositol content, but really only if you’ve got the right gut bacteria to digest phytate. On the flip side, too much phytate can impair mineral absorption, so a better strategy might be to obtain free inositol or inositol-containing phospholipids from organ meats like kidneys. In fact, the lack of organ meat in our modern diet may be contributing to a modern inositol deficiency. That’s discussed in a 2022 paper called “Myo-inositol for insulin resistance, metabolic syndrome, polycystic ovary syndrome and gestational diabetes,” which I’ll link to in the show notes. The same paper talks about how inositol can be depleted or impaired by many modern factors, such as:
Okay. So, that’s the background on inositol. Now, we come to the rather impressive number of studies of inositol for PCOS. For example, there are many clinical trials plus several systematic reviews and even a mention in the 2018 international evidence-based guidelines for PCOS. I almost fell off my chair when I saw a supplement included in those mainstream guidelines. In general, inositol performs well for PCOS, improving many parameters such as lowering androgens, increasing SHBG, promoting weight loss, improving LH to FSH ratio and promoting healthy ovulation and pregnancy. Inositol is generally given at the dose of two to four grams per day as either myo-inositol on its own or as a mix of myo-inositol plus D-chiro-inositol.
And that brings us to a short discussion of the different types or isomers of inositol. There are actually five naturally-occurring isomers or stereoisomers found mostly within cell membranes. Myo-inositol is the most abundant isomer, making up 95 percent of the total free inositol in the body. And one of the jobs of myo-inositol is to act as an intracellular “second messenger” for hormones such as insulin, FSH, and TSH or thyroid stimulating hormone. Which is why myo-inositol has also been trialled for thyroid disease. The topic of a future podcast.
But back to PCOS. Being a second messenger for insulin means that inositol facilitates or enables a normal cell response to insulin, thereby improving insulin sensitivity. And indeed, both myo- and D-chiro isomers can improve insulin sensitivity. Unfortunately, the effect of the two isomers myo- and D-chiro on the ovaries has been a little less clear. Back in the 1990s, the early trials of inositol for PCOS used only D-chiro-inositol—with no myo-inositol—, hoping that by improving insulin resistance, D-chiro-inositol would improve PCOS. But that approach produced some not-great results because, as we now understand, myo-inositol is the isomer that acts as a second messenger for FSH and is therefore essential for ovulation. And, furthermore, it turns out that high insulin in the ovary—as in the situation of PCOS—can cause an abnormally high rate of conversion of myo-inositol to D-chiro-inositol, thereby depleting myo-inositol in the ovary and impairing ovulation. In fact, it’s now been demonstrated that taking too much D-chiro-inositol can actually worsen PCOS via several mechanisms such as increasing androgens, acting as an aromatase inhibitor and thereby lowering estrogen, and by impairing the absorption of the myo-inositol the ovaries need to ovulate.
If you’re a little confused by that, you’re not alone. It is confusing, but fortunately, scientists are on the case and have so far concluded that for PCOS it’s probably best to take either straight myo-inositol or a 40:1 ratio of myo-inositol to D-chiro-inositol, with just enough D-chiro-inositol to improve insulin sensitivity but not so much that it impairs ovarian function. See the paper “Inositol treatment for PCOS should be science-based and not arbitrary,” which I’ll link to in the show notes. There are a few 40:1 formulas on the market, and they’re great. With my patients, I usually just recommend a straight myo-inositol powder because it’s easier to access and cheaper. I recommend a dose of two grams twice daily, so four grams. And the brand I use is labelled only “inositol,” but if you read the fine print, it is myo-inositol.
Myo-inositol is inexpensive and very safe, even when you’re trying for pregnancy. It does not interact with medications and can be combined with other PCOS treatments like metformin, magnesium, and cyclic progesterone therapy. For information about cyclic progesterone, aka natural progesterone for PCOS, see the link in the show notes.
Finally, the absorption of inositol can be impaired by sweeteners such as sorbitol and sucralose. But absorption and action of inositol can be improved by lactalbumin, especially in people with insulin resistance. Lactalbumin is a whey protein.
If you want to ask a question or share your experience with inositol—and please do!—you can visit my forum at LaraBriden.com. I hope that’s been helpful, and thanks so much for listening. Please share and leave a review. And I’ll see you next time when I’ll discuss chronotype and how your body clock affects your metabolism.