Does a high calcium-to-magnesium ratio increase neuromuscular excitability?

The physiological relationship between calcium (Ca²⁺) and magnesium (Mg²⁺) is fundamental to the regulation of bioelectrical activity. Magnesium acts as a natural antagonist to calcium, and an elevated calcium-to-magnesium ratio is scientifically recognized as a driver of neuromuscular hyperexcitability.

Cellular and Molecular Mechanisms

Magnesium serves as a crucial counterbalance to calcium through several distinct pathways:

• NMDA Receptor Regulation: In the central nervous system, magnesium acts as a voltage-dependent pore blocker for N-methyl-D-aspartate (NMDA) receptors. At resting membrane potentials, Mg²⁺ physically obstructs the channel, preventing excessive Ca²⁺ influx. When magnesium levels are low, this block is weakened, leading to neuronal hyperexcitability and potential excitotoxicity.
• Neuromuscular Junction (NMJ) Inhibition: At the NMJ, magnesium competes with calcium for entry through presynaptic P/Q-type voltage-gated calcium channels. By inhibiting this entry, magnesium reduces the evoked release of acetylcholine (ACh), the primary neurotransmitter responsible for muscle contraction.
• Action Potential Thresholds: Low magnesium relative to calcium shifts the action potential threshold of nerve and muscle fibers toward more negative (more easily reached) membrane potentials. This makes tissues more prone to spontaneous firing and lowers the stimulus required for activation.

Neuromuscular and Clinical Effects

When the balance shifts in favor of calcium, the resulting state of hyper-excitability manifests in various clinical symptoms:

• Muscle Dynamics: Magnesium regulates the sarcoplasmic reticulum’s release and sequestration of calcium. In magnesium-deficient states, "calcium overload" in the myofilaments can occur, impairing muscle relaxation and resulting in sustained contractions, tetany, or spasms.
• Symptomatic Presentation: Research indicates that these imbalances are strongly associated with muscle cramps, involuntary twitches (fasciculations), and increased nerve sensitivity.

Bottom line

The claim is well-supported: magnesium acts as a physiological calcium channel blocker that stabilizes membranes. A high calcium-to-magnesium ratio lowers the threshold for nerve firing and impairs muscle relaxation, leading to a state of neuromuscular hyper-excitability.