Magnesium (serum)

Serum magnesium reflects the small circulating fraction of total body magnesium, with roughly 99% stored in bone, muscle, and soft tissue, making serum levels an insensitive indicator of intracellular magnesium status. Magnesium is an essential cofactor for hundreds of enzymatic reactions including ATP synthesis, DNA replication and repair, and serves as a physiological calcium channel antagonist involved in neuromuscular transmission and cardiac rhythm. Hypomagnesaemia (typically below 0.75 mmol/L) is associated with cardiac arrhythmias, neuromuscular excitability, insulin resistance, and increased vascular calcification; it is common in type 2 diabetes, chronic alcohol use, and with prolonged use of proton pump inhibitors or loop diuretics. Epidemiological data link lower habitual magnesium intake and lower serum levels with higher all-cause mortality and accelerated biological aging.