You are nutrient savvy – familiar with many vitamins and minerals, omega-3 fatty acids, proteins, and amino acids. There are other nutrients that you might have noticed on the label of a multivitamin or other supplements that you really haven’t heard much about before.

Inositol is likely one such nutrient. The name probably sounds familiar, but how does your body use inositol? Can your body make it, or do you have to consume it in your diet?

Inositol is found in abundance throughout the body. Isolated from muscle extracts around 1850, it was given the name inositol at that time. The brain and heart contain large concentrations of inositol, and inositol plays an important role in cellular processes from head to toe. In fact, all living cells contain inositol in their membranes, which makes it a significant nutrient for overall health.

The word inositol refers to a diverse group of compounds and is generally used either as a catch-all or interchangeably with myo-inositol, the most abundant form found in nature. Fruits, beans, grains, and nuts are foods with the highest amounts of myo-inositol per serving, and fresh produce tends to contain more inositol than frozen or canned.

The human body can also make inositol from glucose. Although there is not a specific recommended daily intake for inositol, an inositol deficiency or an abnormality in inositol metabolism are both linked to the development of various metabolic health concerns.1

The Role of Inositol in Metabolic Health

Two forms of inositol – myo-inositol and D-chiro-inositol – play a role in how insulin functions. Both types act as a “second messenger,” meaning they help insulin complete its job of moving sugar into cells to use for energy. Here’s a basic overview of the process:

As food digests, blood sugar begins to rise and the pancreas is signaled to release insulin. Insulin travels to cells all over the body where it docks to receptors on the cell surface. Inositol-based molecules transmit a signal from insulin into the cell where it stimulates transporters to rise to the cell surface to bring glucose inside the cell.

How well this process works – how sensitive cells are to insulin signals – is referred to as insulin sensitivity. And when cells lose their ability to optimally respond to insulin, it is called insulin resistance. A deficiency of inositol and/or issues with inositol metabolism are associated with insulin resistance-related conditions, such as polycystic ovary syndrome (PCOS) and metabolic syndrome.2,3

While myo-inositol is the most abundant form of inositol in the body, different tissues require different ratios of myo- to D-chiro-inositol. In the systemic pools within the cells, for example, about 99 percent of inositol is myo-inositol and approximately one percent is D-chiro-inositol. Skeletal muscle, fat, and the liver – some of the main target tissues of insulin – require a higher proportion of D-chiro-inositol, although myo-inositol is still the most abundant form. When working smoothly, the body converts myo- to D-chiro-inositol as needed.

Four Health Benefits of Inositol

  1. Promotes insulin sensitivity and supports balanced blood sugar*

    Both myo-inositol and D-chiro-inositol have been shown in studies to support insulin sensitivity.* In one study, postmenopausal women with metabolic syndrome were placed on a low-energy diet and divided into two groups – 2 grams of myo-inositol or placebo daily for 12 months. The women who took myo-inositol daily maintained a better blood sugar and insulin balance than the women who only changed their diet.*4

    With D-chiro-inositol, the amount seems to be especially important. In a 1999 study, women with PCOS received either 1,200 mg of D-chiro-inositol or a placebo once daily for 6-8 weeks. Supplementation with D-chiro-inositol supported insulin sensitivity.*5 However, when the study was later repeated with higher amounts of D-chiro-inositol, similar results were not achieved.

    More recently, research studies have investigated a combination of myo- and D-chiro-inositol. A 2019 study established the optimal ratio of myo-inositol to D-chiro-inositol for providing nutritional support for women with PCOS. In this study, participants were given either D-chiro-inositol alone or in combination with various ratios of myo- to D-chiro-inositol as 1:3.5, 2.5:1, 5:1, 20:1, 40:1, or 80:1. All forms of supplementation provided support for insulin sensitivity.* However, the 40:1 ratio of myo- to D-chiro-inositol was the most beneficial, while higher concentrations of D-chiro-inositol seemed to hinder benefits.*6 Interestingly, a 40:1 ratio of myo- to D-chiro-inositol is also the naturally occurring ratio of inositol found in plasma.

  2. Supports Balanced Hormone Levels*

    In healthy women of childbearing age, the ovaries produce 25 percent of the testosterone, 50 percent of the androstenedione, and 20 percent of the DHEA circulating in the body. Production of some or all of these androgens is increased in PCOS, usually a result of insulin resistance.7

    The ovaries remain sensitive to the effects of insulin even when other cells in the body become resistant. High insulin levels can adversely affect hormones involved in ovulation, stimulate ovarian cells to produce more androgens, and interfere with ovulation. Elevated androgens can worsen insulin resistance, creating a self-perpetuating cycle of androgen and insulin excess.7

    Inositol most likely supports balanced hormone levels by promoting insulin sensitivity, thereby reducing ovarian exposure to insulin.* Inositol’s role as a second messenger can also modulate hormones, including androgens as well as other hormones involved in ovulation, such as FSH.5,8

  3. Supports Fertility*

    Fertility issues, often associated with PCOS, is another area of inositol research.* Along with supporting insulin sensitivity and balanced hormone levels, myo-inositol appears to help maintain oocyte quality and benefit pregnancy and delivery rates.*7

    Myo-inositol has also been studied in combination with folic acid. In an open-label study of 3,602 women with PCOS who were experiencing fertility issues, myo-inositol plus folic acid promoted ovulation and pregnancy rates.* It was also beneficial for fertilization rates in a subgroup of women undergoing IVF.*9 Similarly, in a double-blind trial in which women received either myo-inositol plus folic acid or folic acid alone, the combination promoted fertilization rates better than folic acid alone.*10

  4. Enhances Mood*

    In the brain, inositol enhances the communication between brain cells and is believed to play a role in neurotransmitter synthesis.* More specifically, inositol helps increase serotonin receptor sensitivity, which in turn, promotes the release of GABA, a calming neurotransmitter in the brain.*11

    For women who have PCOS, anxious feelings and changes in mood are common. Research indicates both physiological and social/emotional factors correlate with PCOS-related changes in mood. Physiologically, imbalances in insulin, cortisol, serotonin, and inflammatory response appear to play a role.12

    Similarly, hormone and neurotransmitter imbalances might be responsible for the mood changes experienced during menstruation. In a meta-analysis of studies on inositol and mood, inositol improved mood and offered nutritional support for women with PMS.*12,13

    Thorne’s Ovarian Care contains the naturally occurring ratio of 40:1 myo-inositol to D-chiro-inositol found in clinical studies to provide numerous health benefits.* In addition, the CoQ10, folate, and polyphenols in the formula provide further support for balanced hormone levels, oocyte health, fertility, and a healthy insulin response.*

References

  1. Caputo M, Bona E, Leone I, et al. Inositols and metabolic disorders: From farm to bedside. J Tradit Complement Med 2020;10(3):252-259. doi:10.1016/j.jtcme.2020.03.005
  2. Muscogiuri G, Palomba S, Laganà AS, Orio F. Inositols in the treatment of insulin-mediated [conditions]. Int J Endocrinol 2016;2016:1-6. doi:10.1155/2016/3058393
  3. Dinicola S, Minini M, Unfer V, et al. Nutritional and acquired deficiencies in inositol bioavailability. Correlations with metabolic disorders. Int J Mol Sci 2017;18(10):2187. doi:10.3390/ijms18102187
  4. Santamaria A, Giordano D, Corrado F, et al. One-year effects of myo-inositol supplementation in postmenopausal women with metabolic syndrome. Climacteric 2012;15(5):490-495. doi:10.3109/13697137.2011.631063
  5. Nestler JE, Jakubowicz DJ, Reamer P, et al. Ovulatory and metabolic effects of D-chiro-inositol in the polycystic ovary syndrome. N Engl J Med. 1999;340(17):1314-1320. doi: 10.1056/NEJM199904293401703.
  6. Nordio M, Basciani S, Camajani E. The 40:1 myo-inositol/D-chiro-inositol plasma ratio is able to restore ovulation in PCOS patients: comparison with other ratios. Eur Rev Med Pharmacol Sci 2019;23(12):5512-5521. doi:10.26355/eurrev_201906_18223
  7. Kalra B, Kalra S, Sharma J. The inositols and polycystic ovary syndrome. Indian J Endocrinol Metab 2016;20(5):720. doi:10.4103/2230-8210.189231
  8. Laganà AS, Garzon S, Casarin J, et al. Inositol in polycystic ovary syndrome: Restoring fertility through a pathophysiology-based approach. Trends Endocrinol Metab 2018;29(11):768-780. doi:10.1016/j.tem.2018.09.001
  9. Regidor PA, Schindler AE, Lesoine B, Druckman R. Management of women with PCOS using myo-inositol and folic acid. New clinical data and review of the literature. Horm Mol Biol Clin Investig 2018;34(2):/j/hmbci.2018.34.issue-2/hmbci-2017-0067/hmbci-2017-0067.xml. doi:10.1515/hmbci-2017-0067
  10. Mohammadi S, Eini F, Bazarganipour F, et al. The effect of myo-inositol on fertility rates in poor ovarian responder in women undergoing assisted reproductive technique: a randomized clinical trial. Reprod Biol Endocrinol 2021;19(1):61. doi:10.1186/s12958-021-00741-0
  11. PubChem Compound Summary for CID 892, Inositol. In: National Center for Biotechnology Information. https://pubchem.ncbi.nlm.nih.gov/compound/892#section=Pharmacology-and-Biochemistry [Accessed August 15, 2022.]
  12. Cantelmi T, Lambiase E, Unfer VR, et al. Inositol treatment for psychological symptoms in polycystic ovary syndrome women. Eur Rev Med Pharmacol Sci 2021;25(5):2383-2389. doi:10.26355/eurrev_202103_25278
  13. Mukai T, Kishi T, Matsuda Y, Iwata N. A meta-analysis of inositol . . . . Hum Psychopharmacol Clin Exp 2014;29(1):55-63. doi:10.1002/hup.2369