The amount of magnesium that is absorbed by the body when we take a supplement depends on the form (ie, complex) the magnesium is delivered in (think glycinate, oxide, etc.) but also our internal magnesium levels, or status. Someone who is magnesium deficient (has a blood serum level below 0.75 mmol/L) will generally absorb more of the mineral than someone who is not.
Infusing a bit more nuance into the assessment of magnesium levels in the body, Ferira shares that, “some health care practitioners, especially those with a functional or integrative focus, choose to assess magnesium status with red blood cell (RBC) levels instead of plasma or serum due to the higher magnesium content in RBCs, but even that test has its challenges in capturing the whole-body magnesium status situation.”
It’s a mineral complex. Utilized for over 300 essential cellular pathways in the body, it’s no wonder we would benefit from a sufficient supply of magnesium daily. “Your body is constantly using up magnesium and the amount that you store is regulated,” registered dietitian Tracey Frimpong, RD, tells mbg. On average, she adds, about 40% of the magnesium we consume is absorbed in the upper GI tract, while 5% is absorbed lower down in the large intestine (ie, colon).
One of the reasons it can be challenging to accurately measure magnesium levels in the blood is because of where it preferentially concentrates in the body. “Interestingly, 99% of the mineral is located in our bones (about 50 to 60%), while the rest is found in muscle and other soft tissues,” explains Ferira.
This ongoing process of absorption and utilization is pretty quick, so it’s important to make sure you’re always giving your body the magnesium it needs. “Most magnesium will stay in the body for anywhere from 12 to 24 hours. So it’s not something you can just take once, see results, and then never take again,” explains registered dietitian Amanda Li, RD
This means that as you’re looking to fulfill your nutritional requirements through rich dietary sources (like green leafy vegetables, legumes, nuts, seeds, and whole grains) and high-quality supplements, you would want to take advantage of that magnesium supplement at least once a day.
Though the exact cadence will depend on the form you’re taking—be it magnesium bisglycinate, citrate, chloride, etc., or even a comprehensive multivitamin that contains magnesium—and what you’re taking it for.