Magnesium: Deficiency in Half of Adults, Bioavailability of Forms, and Effects on Blood Pressure and Glycemia

How widespread is magnesium deficiency?

Magnesium participates in more than 300 enzymatic reactions — from ATP synthesis and DNA replication to ion channel regulation. Yet it is among the most deficient nutrients in industrialized countries.

A review by Zhang and Zhao (International Journal for Vitamin and Nutrition Research, 2025) drawing on global modeling across 185 countries found that approximately 2.4 billion people, or ~31% of the world population, consume magnesium below the estimated average requirement (EAR). According to US NHANES survey data cited in a scoping review by Costello, Fan, and Wallace (Nutrients, 2025, 48 studies), about 50% of US adults do not meet this norm. Among male adolescents aged 14–18 the average intake is about 78% of the EAR, and among women over 75 about 63%.

The main causes: industrial food processing reduces magnesium content, grain refining removes up to 80% of magnesium, and baseline soil content has declined over recent decades. Caffeine and alcohol increase renal excretion; proton pump inhibitors impair absorption.

Why does the form of a magnesium supplement matter?

Magnesium oxide — the most common and inexpensive form — is simultaneously the least bioavailable. A randomized crossover study by Kappeler and colleagues (BMC Nutrition, 2017, n=20) compared citrate and oxide: citrate significantly increased 24-hour urinary magnesium excretion (p < 0.05), while oxide produced no significant response compared with baseline. Plasma magnesium levels were significantly higher after citrate at 4 and 8 hours.

A systematic review of 14 studies by Pardo and colleagues (Nutrition, 2021) confirmed the general pattern: organic forms (citrate, lactate, malate) are more bioavailable than inorganic ones. Bioavailability data for magnesium oxide from individual studies indicate a considerably lower percentage of absorption compared with organic forms — explaining why oxide's low cost is offset by the higher dose required for effect.

Magnesium L-threonate (Magtein) is the only form that in preclinical models has shown the ability to cross the blood-brain barrier, making it the subject of research on cognitive function. Human data on brain penetration are not yet available; existing RCTs were funded by the manufacturer.

How does magnesium affect blood pressure?

The most comprehensive meta-analysis to date is by Argeros and colleagues (Hypertension, 2025; 38 RCTs, n=2,709, median 12 weeks, median dose 365 mg/day elemental magnesium):

• Systolic pressure: −2.81 mmHg (95% CI: −4.32 to −1.29; p < 0.001)
• Diastolic pressure: −2.05 mmHg (95% CI: −3.23 to −0.88; p < 0.001)

Subgroup analysis showed the effect substantially amplified in groups with baseline hypomagnesemia:

• Systolic in hypomagnesemia: −5.97 mmHg (95% CI: −8.52 to −3.41; p < 0.001)
• Diastolic in hypomagnesemia: −4.75 mmHg (95% CI: −6.59 to −2.92; p < 0.001)

Among hypertensive patients on medication, systolic pressure decreased by 7.68 mmHg (p=0.003). In normotensive individuals without deficiency no statistically significant effect was found. A dose-response relationship was not confirmed — suggesting a threshold rather than a linear mechanism.

What is magnesium's role in glycemic regulation and insulin resistance?

Magnesium participates in the function of the insulin tyrosine kinase receptor: its deficiency reduces insulin sensitivity. Clinical data support this link.

A meta-analysis by Asbaghi and colleagues (British Journal of Nutrition, 2022; 18 RCTs, n=1,097 patients with type 2 diabetes) found:

• HbA1c at 500 mg/day: −0.73% (95% CI: −1.25 to −0.22; p=0.004)
• Fasting glucose after 24 weeks: −15.58 mg/dL (95% CI: −24.67 to −6.49; p=0.034)
• HbA1c after 24 weeks: −0.48% (95% CI: −0.77 to −0.19; p=0.001)

Dosage and duration were key: at lower doses and less than 24 weeks, effects are weaker and often non-significant.

For the prediabetes stage, a meta-analysis by Basit and colleagues (Journal of Diabetes & Metabolic Disorders, 2025; 5 RCTs, n=384) found:

• Post-load glucose (2-h OGTT): −0.99 mmol/L (p < 0.00001)
• HOMA-IR: −1.10 (p=0.03)
• Triglycerides: −14.57 mg/dL (p=0.04)
• HDL: +3.87 mg/dL (p=0.04)

What do data on inflammation and oxidative stress show?

A systematic review and meta-analysis by Cepeda and colleagues (Antioxidants, 2025; 28 studies, 6 in the meta-analysis) on CRP: standardized mean difference = 0.21 (95% CI: 0.09–0.32; p=0.008) — a small but statistically significant effect size in favor of reduced inflammation. An important caveat: most included studies used magnesium in combination with other micronutrients, and only 4 used magnesium alone.