Magnesium RDI in Australia: how much do you need each day?

Written by Cassie, registered pharmacist
Founder of Clean Green Safe

If you’ve ever stood in the supplement aisle, bottle in hand, wondering how much magnesium you actually need, please know you’re not alone. It’s one of the questions I’m asked most often in the pharmacy, and the numbers on labels don’t always make it easy.

So let’s take it gently, one step at a time. By the end, you’ll know your own daily target, the one limit worth keeping in mind, and how to read your label with confidence.

What does RDI actually mean?

RDI stands for Recommended Dietary Intake. It’s the amount of a nutrient that meets the needs of nearly all healthy people. In Australia and New Zealand, these are set by the NHMRC. You might also see “NRV” on some labels and websites, especially from overseas. In the Clean Green Safe app, we simply call these your daily nutritional targets.

How much magnesium do you need each day?

Your target depends on your age and stage of life. These are the NHMRC daily targets for magnesium, and they include everything you get from food as well as supplements:

• Men 19 to 30: 400 mg
• Men 31 and over: 420 mg
• Women 19 to 30: 310 mg
• Women 31 and over: 320 mg
• Teenagers 14 to 18: 410 mg for boys, 360 mg for girls
• Pregnancy: 350 mg (19 to 30) or 360 mg (31 to 50)
• Breastfeeding: 310 mg (19 to 30) or 320 mg (31 to 50)

Here’s the reassuring part. Your food counts toward this target too. Leafy greens, nuts, seeds, legumes and wholegrains are all lovely sources of magnesium, so you’re likely getting a good share of what you need before you even open a supplement.

Is there a limit on magnesium supplements?

Yes, and it’s the one number I’d love everyone to know. The NHMRC upper limit for adults is 350 mg a day, and it applies only to magnesium from supplements and medicines, not from food.

I know this can feel confusing, because it’s lower than the daily target for most adults. It isn’t a mistake. Your target covers everything you eat, while the upper limit is about supplements on their own. Larger doses from supplements are more likely to upset your tummy or cause diarrhoea, and that’s what the limit is there to protect you from.

So please don’t feel your supplement has to do all the work. Think of it as a gentle top-up to the magnesium you already get from your meals.

Why does the number on my label look so big?

This is where so many people get caught out, and it’s completely understandable. Magnesium is measured in milligrams (mg). One gram is 1,000 mg, so if you see “1 g” or “1,000 mg” on the front of a pack, it’s almost always describing the whole compound, not the magnesium itself.

That’s because magnesium always comes joined to something else, like oxide, citrate or glycinate. The compound weight is often the biggest number you’ll see. The amount that counts toward your daily target is the elemental magnesium, which is usually written as “equivalent to magnesium”.

To show you how much this can vary:

• Magnesium oxide 500 mg gives you about 300 mg of magnesium
• Magnesium citrate 500 mg gives you about 80 mg of magnesium
• Glycinates and chelates vary, so look for the “equivalent to magnesium” line

Want the maths done for you? Try our mineral calculator.

If you’d like to understand this a little more, our magnesium guide and our article on elemental vs salt-form dosing explain it in more detail.

Taking magnesium glycinate? See how much magnesium is really in magnesium glycinate, and the top-rated options.

Could you be getting more than you think?

Magnesium has a way of turning up in lots of places, including multivitamins, sleep and stress formulas, sports powders and some calcium products. If you take two or three of these, it can add up more quickly than you’d expect.

Many magnesium products also contain vitamin B6, so it’s worth having a look for that too. I’ve explained why in Is there vitamin B6 hiding in your magnesium?

Three simple checks you can do today

• Find the “equivalent to magnesium” amount on each label.
• Multiply it by the number of tablets or capsules you actually take each day.
• Add up every product you take. Aim to keep your total from supplements at or under 350 mg a day, unless your doctor has advised you otherwise.

If you have kidney problems, take other medicines, or simply aren’t sure whether magnesium is right for you, please have a chat with your pharmacist or GP. There’s no such thing as a silly question, and we’re always happy to help.

ABOUT THE AUTHOR

Cassie, registered pharmacist

Cassie is a registered pharmacist, a parent and the founder of Clean Green Safe. With a background in Australian supplement regulation across the TGA, FSANZ and NHMRC, she built Clean Green Safe to help people understand what’s really in their supplements, and how it all adds up across everything they take.