The B-complex vitamins run from B1 (thiamine) to B12 (cobalamin), skipping a number between B7 (biotin) and B9 (folate). This gap often raises the question of whether a Vitamin B8 ever existed. An active molecule did once hold that designation, but its status changed due to a deeper understanding of human biology. This compound, now recognized for its roles in cellular communication and metabolic health, remains a subject of ongoing scientific interest despite its declassification.
The Identity of Vitamin B8
The compound historically known as Vitamin B8 is Inositol, specifically the stereoisomer called myo-inositol. This molecule is a cyclic sugar alcohol, structurally similar to glucose. Scientists initially grouped it with the B vitamins during the mid-20th century because it is water-soluble and appeared necessary for the health of certain organisms, leading to its temporary classification.
Inositol’s classification as a true vitamin was withdrawn because it did not meet the strict criteria of being an essential nutrient. The body cannot produce essential nutrients and must obtain them through diet. However, the human body can synthesize its own Inositol, primarily in the kidneys and liver, by converting glucose.
Because the body is capable of endogenous production, Inositol is now scientifically designated as a vitamin-like compound or a pseudovitamin. Although the official numerical designation is obsolete, the molecule plays a significant functional role in numerous physiological processes. Its most common and biologically active form, myo-inositol, is the direct precursor to several crucial signaling molecules.
Key Functions of Inositol
Inositol’s most fundamental role is functioning as a precursor for secondary messengers within cells. When hormones or neurotransmitters bind to exterior receptors, they rely on these internal messengers to transmit instructions since they cannot enter the cell. Inositol is converted into molecules like inositol trisphosphate (IP3), which relay signals from the cell surface to the nucleus and other internal structures.
This signaling mechanism is particularly important in regulating the body’s response to insulin. Specific inositol-derived molecules, known as inositol phosphoglycans, act as secondary messengers that carry the insulin signal. This process is necessary for glucose uptake and storage, allowing Inositol to help maintain healthy blood sugar control and proper metabolic function.
Beyond metabolism, Inositol is an integral structural component of all cell membranes, incorporated into phospholipids. It is highly concentrated in the brain and central nervous system, where it influences neurotransmitters like serotonin and dopamine. This involvement is why Inositol has been studied for its potential role in balancing mood and supporting nerve function. Furthermore, it has a lipotropic function, helping to mobilize and metabolize fats.
Dietary Sources and Supplementation
Since the body can synthesize Inositol, a deficiency is generally considered rare in healthy individuals. The average daily intake from a typical diet is estimated to be around 720 milligrams to one gram. The compound is widely distributed in the food supply, found in whole grains, nuts, beans, and fresh fruits like cantaloupe and citrus varieties.
The primary form of Inositol in plants is phytic acid, or inositol hexaphosphate (IP6), which stores phosphorus in seeds and bran. The body’s digestive processes release the usable Inositol molecule from this consumed form. Highest concentrations are found in foods like chickpeas, buckwheat, and some organ meats.
Inositol is also available as a dietary supplement, often used at higher doses than what is obtained through diet. Supplementation has been explored for supporting metabolic health, particularly in conditions like insulin resistance and Polycystic Ovary Syndrome (PCOS). Dosages for these metabolic concerns often range from 2 to 4 grams daily.
Significantly higher doses, sometimes between 12 and 18 grams daily, have been investigated for their effects on mood and mental health. Inositol supplements are generally well-tolerated, with side effects typically limited to mild gastrointestinal discomfort at higher doses. Despite its non-vitamin status, Inositol remains an important, biologically active molecule that continues to be a focus of health research.