Inositol

Inositol is one of the few supplements where the form and the dose decide almost everything, so these are the questions our naturopaths ask in store to make sure you choose the right one.

A good fit if

• Your cycle is the reason you're here. That's where the most repeated finding in the research is.
• You'll take myo-inositol at the dose the trials used, four grams a day split into two, rather than a token amount
• You'd rather start with the form that has nearly all the evidence than a ratio that's still being debated
• You're thinking ahead about preconception health and will check with your practitioner first
• You want something easy to live with. It's generally well tolerated, and a mild upset tummy is the usual complaint.

Check with us first if

• You take lithium or valproate. These medicines work partly by lowering inositol in the brain, and the only reassurance on record is one small open study of fifteen people, with no comparison group and no blinding.
• You take metformin or another diabetes medicine. Inositol is often given alongside them in trials, but you're on a prescribed medicine and your prescriber should know.
• You're looking at D-chiro-inositol on its own, or a product weighted towards it. The largest review of the research says D-chiro-inositol on its own should be used with caution.
• Your kidneys don't work well. Inositol is cleared through the kidneys, and we found no dosing study in people with reduced kidney function.
• You're buying it for a teenager. There's only one small trial, it didn't reach its main goal, and that's not enough to make this something to choose on your own.
• You're trying to conceive. Preconception health is a good reason to ask us, and the rest of that conversation belongs with your practitioner.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before starting.

• Inositol. Best known for: The general name, and the only one that appears in Schedule 1, at item 2700. In practice a product labelled simply inositol is myo-inositol, because that's the form that dominates both food and the human body. Absorption: Same as myo-inositol; nothing separate is described in the evidence we reviewed. Typical use: The umbrella name. It carries the family's regulatory position, while whichever form the product actually contains carries the evidence.
• Myo-inositol. Best known for: The workhorse. It's most of the inositol in your body and in your food, and the form behind nearly all the research. It increases aromatase and FSH receptor activity in the ovary. Absorption: Standard doses by mouth reach the trial effect at two grams twice a day. The often-repeated claim that alpha-lactalbumin fixes inositol absorption rests on a paper that has since been retracted, so we don't repeat it. Typical use: Cycle regularity across 26 trials, carbohydrate metabolism, sperm movement, and the four grams a day used in the pregnancy research.
• D-Chiro-Inositol. Best known for: The form involved in insulin signalling, present in blood at roughly one fortieth the level of myo-inositol. It acts the opposite way in the ovary: high levels increase androgen production and lower aromatase. Absorption: Not separately described in the evidence we reviewed. Typical use: Small amounts alongside myo-inositol. Trial doses range from 13.8 mg to 500 mg twice daily, a 36-fold range, and the largest review of this research says using it on its own should be done with caution.
• Myo-Inositol and D-Chiro-Inositol 40:1. Best known for: Copies the ratio the two forms naturally have in your blood, about forty to one. Absorption: Same as myo-inositol. Typical use: Usually two grams of combined inositols twice a day. Check the total, not just the ratio: 40:1 at four grams a day and 40:1 at 1.1 grams a day are different products, and the low-dose version didn't repeat what the four-gram one did.

Reference values. There aren't any. Inositol isn't in the NHMRC Nutrient Reference Values for Australia and New Zealand, because your body makes its own from glucose. So there's no recommended dietary intake, adequate intake or upper level. You'll still see it sold as 'vitamin B8', but it isn't a vitamin, there's no Australian reference value behind that name, and we don't use it.

Typical supplemental range. Dose is the choice that matters most here, because it's what separates the trials that found something from the ones that didn't. Almost all the research used myo-inositol at four grams a day, taken as two grams twice a day, for twelve weeks to six months. Products based on the 40:1 ratio were given either as two grams of combined inositols twice a day, or as a much smaller 1,100 mg of myo-inositol plus 27.6 mg of D-chiro-inositol a day, and those two aren't the same product. D-chiro-inositol on its own has been tested from 13.8 mg twice a day (inside a 40:1 combination) up to 500 mg twice a day, a 36-fold range. Anything giving you less than a gram of myo-inositol a day is below every dose that had an effect in these trials.

Upper level. None has been set. There's no maximum recommended daily dose for it on Australia's permitted ingredients list (Schedule 1, item 2700), and no NHMRC upper level because inositol has no nutrient reference value. Four grams a day is the highest dose regularly studied, and the lack of a cap doesn't mean higher doses are proven safe. We also found no dosing study in people with reduced kidney function, which matters because inositol leaves your body through the kidneys.

Worth knowing. The trials ran for twelve weeks to six months and measured results at three and six months, so this isn't something that works in the first week. For children and teenagers, the only trial we found used 2,000 mg a day with zinc for three months and didn't reach its main goal, which isn't a reason to give it to a child without medical supervision. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Cereals: named by Cochrane as a common dietary source; no per-serve figure is available, so none is stated
• Corn: as above: a named source without a published per-serve amount
• Legumes: as above: a named source without a published per-serve amount
• Meat: as above: a named source without a published per-serve amount
• Your own body: you make inositol from glucose, which is why it has no recommended daily intake
• What food can't do: the four grams a day used in the trials is far more than an ordinary diet supplies

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• Premature and newborn babies. Don't give it. Six trials in 1,194 babies found no benefit for retinopathy of prematurity and, on further analysis, higher death rates (RR 1.55).
• You're pregnant. This is a decision for a practitioner, not something to choose yourself; the trial evidence is rated low to very low certainty.
• You're breastfeeding. We found no trial, review or safety statement. That means unknown, not safe.
• You take lithium or valproate. These medicines work by lowering inositol in the brain and nervous system, so check with your prescriber before using it.
• You take metformin or other diabetes medicines. They were often taken together in trials, but your prescriber should know.
• You'd be taking D-chiro-inositol at a high dose or high proportion. High levels increase androgen production and lower aromatase, the opposite of what's wanted if you're trying to conceive.
• Children and teenagers. There's one small trial, which missed its main goal; there isn't enough data to use it outside clinical supervision.
• You have reduced kidney function. Inositol is cleared by the kidneys and we found no dosing study for people with kidney problems.
• You plan to take it for longer than six months. Long-term use hasn't been studied in the evidence we reviewed.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before starting.