Inositol is a carbocyclic sugar, chemically related to glucose, found widely in nature and within the human body. Although historically called Vitamin B8, it is not a true vitamin because the body can synthesize it and does not strictly require it from the diet. It plays a role in various cellular processes, including forming structural components of cell membranes and acting as a signaling molecule. Inositol can be obtained through both diet and concentrated supplemental forms.
Natural Dietary Sources
In plant-based foods, inositol is predominantly found as phytic acid, also known as inositol hexaphosphate (IP6). This molecule serves as the main storage form of phosphorus in many plants, containing six phosphate groups attached to an inositol ring. The most common form of inositol available from food is myo-inositol.
Whole grains, seeds, nuts, and legumes are the primary dietary sources of phytic acid. Cereals can contain between 0.04% and 3.3% phytic acid, while nuts can range up to 9.4%. Specific foods recognized for their inositol content include cantaloupe, citrus fruits like oranges, brown rice, and various beans.
Food processing affects the amount of available inositol from these sources. Refining grains, such as milling whole wheat into white flour, removes the outer bran layer where most phytic acid is concentrated, significantly reducing the final inositol content. Conversely, techniques like soaking and sprouting legumes can partially break down phytic acid, enhancing the bioavailability of myo-inositol. A typical Western diet provides approximately one gram of inositol per day.
Understanding Supplemental Forms
When dietary intake is insufficient or a higher, concentrated dose is desired, inositol is commercially available as a supplement. Supplementation allows for the intake of several grams per day, far exceeding what is obtainable through diet alone. Commercial products typically focus on two of the nine possible stereoisomers: Myo-inositol (MI) and D-chiro-inositol (DCI).
Myo-inositol is the most abundant form in nature and the human body, but D-chiro-inositol serves a distinct biological function. Many supplements combine these two forms in a specific 40:1 ratio of MI to DCI. This ratio mirrors the physiological concentration found in healthy human plasma, suggesting a balance optimal for cellular function.
This targeted combination supports the complex signaling pathways in which both forms are involved. Supplements are widely available in convenient formats, most often sold as a fine powder that can be mixed into liquids or encapsulated into vegetable capsules. These concentrated forms bypass the variability of dietary absorption and processing.
Inositol Synthesis and Storage in the Body
The body produces its own inositol through a process called de novo synthesis. This internal production starts with glucose-6-phosphate, a derivative of glucose, which is then converted into myo-inositol. The kidneys are the primary organs responsible for this synthesis, although other tissues contribute to the overall pool.
Once synthesized or absorbed, inositol is not distributed uniformly throughout the body. It is highly concentrated in specific tissues where it performs specialized functions. The brain, heart muscle, and cerebrospinal fluid maintain higher levels of inositol compared to circulating blood.
Within cells, inositol is transported across the cell membrane by specific sodium-ion coupled transporters. A significant portion is then incorporated into the structure of cell membranes as phosphoinositides, which are lipid molecules that act as precursors for various cell-signaling messengers.