Inositol refers to a group of molecules (isomers) that are structurally similar to glucose and involved in cellular signaling.^[1][2] Inositol is synthesized in the human body, but is also obtained in the diet from foods like citrus fruits, bran, beans, nuts, and seeds.^[3][4][5] Inositol is also taken as a dietary supplement. The majority of inositol supplements contain the myo-inositol form, as it is the most plentiful type of inositol found in the body.^[6]

Because supplementation with inositol can increase insulin sensitivity and help improve fasting glucose and postprandial glycemic control,^[7][8] inositol might help prevent and/or treat diabetes. One type of diabetes for which the role of inositol has been widely studied is gestational diabetes, a condition characterized by abnormal glucose tolerance and high blood sugar during pregnancy. Meta-analyses show that supplementation with inositol during pregnancy might reduce the incidence of gestational diabetes and related birth complications.^[9][10][11] However, further high-quality randomized controlled trials are needed to determine whether inositol is efficacious in the treatment of gestational diabetes.^[12]

Inositol shows promise for the management of polycystic ovary syndrome (PCOS),^[13][14][15] a condition characterized by high androgen levels, infertility, and abnormalities in glucose metabolism in women. However, given the small number of studies, the small sample sizes of these studies, and the general low quality of the evidence, further research is needed before firm conclusions can be made.

Supplementation with inositol may also help support weight loss: some evidence shows it can reduce body mass index (BMI) in people with overweight or obesity.^[16] Supplementation with inositol may also reduce blood pressure, triglycerides, total cholesterol, and LDL cholesterol.^[17][18] However, the confounding effects of dietary intake and physical activity — factors that independently influence weight loss, blood lipids, and blood pressure — have not been clearly controlled in many studies. Consequently, there is a need for further randomized controlled trials examining the direct effect of inositol on these outcomes.

Although studies examining the safety of intravenously-administered inositol in preterm infants do not find a greater incidence of adverse events compared to placebo,^[19][20][21] a thorough dose-response study of orally-administered inositol assessing safety and side effects is currently lacking. Consequently, the side effects of inositol are not clearly defined. However, while many randomized controlled trials of inositol fail to report side effects,^[7] meta-analyses typically conclude that side effects following supplementation with inositol are not common.^{[7][12][9][11][15]} That said, gastrointestinal problems like nausea and diarrhea have been documented at very high orally-administered doses (e.g., up to 12 grams of inositol per day) in adults.^[22][6]

Inositols are molecules naturally present in the body with a role in various cellular signaling pathways.^[6][23][24] The most robust effect of supplementation with inositol is on blood glucose control,^{[7][8][9][10][11]} and this effect may be explained by inositol’s role in insulin signaling and its ability to increase insulin sensitivity.^[6][23][24] However, further research is needed to fully understand the mechanism(s) of action.^[1][2]