Magnesium is calcium's essential partner — without enough magnesium, calcium can't properly integrate into bone matrix, and Vitamin D can't function optimally either. Most Canadians don't get enough. But the supplement market is full of magnesium products that barely absorb, and the r/Supplements community has this right: magnesium oxide is largely a waste of money.
About 60% of the body's magnesium is stored in bone. It plays several roles in bone health:
Several observational studies have found associations between higher dietary magnesium intake and better bone density in older adults. Whether supplementing magnesium in people who aren't deficient produces additional bone benefit is less clear — the strongest case is for correcting deficiency, not supplementing beyond normal levels.
Health Canada's Dietary Reference Intakes:
| Group | Recommended Daily Intake | Upper Tolerable Limit (supplements) |
|---|---|---|
| Adult men 19-30 | 400 mg/day | 350 mg/day from supplements |
| Adult men 31+ | 420 mg/day | 350 mg/day from supplements |
| Adult women 19-30 | 310 mg/day | 350 mg/day from supplements |
| Adult women 31+ | 320 mg/day | 350 mg/day from supplements |
| Pregnant women | 350-360 mg/day | 350 mg/day from supplements |
Note: the upper limit applies to supplemental magnesium only — not dietary magnesium from food. High-dose supplemental magnesium causes diarrhea, which is both unpleasant and a sign your gut isn't absorbing it anyway.
| Form | Absorption | Best For | Verdict |
|---|---|---|---|
| Magnesium glycinate | High | Bone health, sleep, anxiety — well tolerated | ✅ Best overall |
| Magnesium citrate | High | Bone health, constipation, general supplementation | ✅ Excellent choice |
| Magnesium malate | High | Muscle fatigue, fibromyalgia symptoms | ✅ Good for muscle focus |
| Magnesium threonate | High (brain-specific) | Cognitive function — specific brain bioavailability | ⚠️ Premium price, niche use |
| Magnesium oxide | Very low (~4%) | Laxative effect, cheap | ❌ Skip for bone health |
| Magnesium chloride | Moderate | Topical use; oral absorption is reasonable | ⚠️ Fine, not optimal |
Magnesium oxide is the form in the cheapest supplements and many multivitamins. Its absorption rate is around 4% — you excrete most of it. The r/Supplements community has reached strong consensus on this: if you're supplementing magnesium for any health reason, oxide is the wrong choice. Glycinate or citrate absorb at 30-40%+ and have comparable pricing when you calculate cost per absorbed milligram.
Both absorb well. Glycinate tends to be gentler on the digestive system and is often recommended for people who experience loose stools with citrate. Citrate has a mild laxative effect even at normal doses in some people — useful if you're constipated, not if you're not.
For pure bone health focus, either works. Many people find glycinate better tolerated before bed, since the glycine component has mild calming properties.
Food-first is always the right approach. The best dietary sources of magnesium:
A diet that regularly includes nuts, seeds, legumes, and leafy greens will come close to meeting magnesium needs. The people most likely to fall short: those eating primarily processed foods, low-carb/keto diets that eliminate legumes and grains, and older adults with reduced absorption.
Magnesium is best taken with food — it absorbs better and is less likely to cause digestive issues. Avoid taking it at the same time as calcium supplements if you're taking both: calcium and magnesium compete for the same intestinal transport. Separate them by 2 hours.
Evening is a popular timing choice, not just for the absorption benefit but because magnesium glycinate in particular seems to support sleep quality in some people — reasonable to take advantage of if bone health is your primary goal.