Why Magnesium Rocks

You're reading this post, which implies at least an interest in the greatest specialty on the planet.

It also suggests you probably already love magnesium and don't need an entire post devoted to explaining why it's wonderful.

But you're getting one anyway.

Because we love magnesium that much.

Why does it come up in exams so much?

You might notice through your Tolkien-esque adventure towards the FRCA examinations that certain topics repeatedly get examined more frequently than others:

• Pyloric stenosis
• Thyroidectomy
• Ocular anatomy
• Paediatric MRI
• Magnesium pharmacology

The reason for this is these topics sit nicely at the intersection of multiple subjects - anatomy, physics, physiology, pharmacology - making them an efficient way to assess the breadth of your knowledge.

Despite being a humble bivalent cation, magnesium is implicated in myriad aspects of physiology, pharmacology, obstetrics, critical care, pain management, as well as cardiac and respiratory emergencies.

The ion that needs no introduction

Magnesium is the ninth most abundant element in the universe, and the fourth most abundant cation in the body.

It is also the second most abundant intracellular cation after potassium.

Every cell needs it, over 300 enzymes use it as a co-factor, and even the legendary ATP likes to hang out as a chelate of magnesium ions.

Where is it?

• You have around 24 g of magnesium in your body
• Most of it (60%) just chills out in the bones
• The rest is mostly intracellular (20% in skeletal muscle)
• About 1% sits in the extracellular space, and only a small proportion of this is in the blood

So clearly measuring your serum magnesium concentration isn’t going to tell you all that much about your total body stores.

What does it do?

The ultimate Swiss army knife molecule, magnesium is simultaneously an:

• Electrolyte
• Membrane stabiliser
• Anticonvulsant
• Anti-arrhythmic
• Bronchodilator
• Sympatholytic
• Anaesthetic and analgesic adjunct
• Laxative - check out this bonkers case
• Antacid (milk of magnesia)

It's less of a drug, and more of a multisystem modulator, interacting with the three major ions and their conduction channels:

• Sodium
• Potassium
• Calcium

Given these channels are found literally everywhere in the body, it's hardly surprising that magnesium has a wide array of multisystem effects that can be useful, annoying or even toxic.