What is Magnesium?

Magnesium is a cofactor, a mineral an enzyme needs present before it can work: hundreds of reactions will not run without it, the ones that produce energy among them. It also helps nerves and muscles relax once they have fired.

Calcium triggers nerve and muscle contraction where magnesium helps the same tissues relax, so measuring both shows whether a change in signalling belongs to one mineral or to both. A magnesium shortage makes the kidney waste potassium in urine, so the two fall together, and potassium can be the marker that moves while magnesium is the cause.

Intake comes from nuts, seeds, wholegrains and green vegetables. The gut adapts to how much arrives, taking up a larger share of a small intake and a smaller share of a large one, which softens the effect of diet on the blood amount. Day to day, the kidney sets the balance through how much it passes into urine.

Blood magnesium moves across weeks as diet, gut absorption or what the kidney passes out change, not hour by hour the way sodium and potassium do. One sample therefore stands for the weeks behind it rather than the morning of the test. A year between samples is long enough that a difference between them means one of those three influences has shifted and stayed shifted. This is Do Health's monitoring schedule, not a general recommendation for everyone.