Magnesium Absorption: Which Form Is Best?

Magnesium is an essential alkaline earth metal and the second most abundant intracellular cation in the human body. It is naturally present in numerous minerals and plays a vital role in many physiological processes.

Studies have shown that people in most European countries consume less magnesium than recommended by the World Health Organization (WHO) [1]. One study involving 115 university students found both lower-than-recommended plasma magnesium concentrations (0.76 mmol/L) and inadequate dietary magnesium intake (8.84 mmol/day) [2]. Other reports suggest that particular attention should be paid to older adults and young women, who are especially vulnerable to magnesium deficiency [3].

Disturbances in magnesium homeostasis occur when magnesium intake decreases or urinary and gastrointestinal losses increase. Magnesium is obtained primarily through the diet [1–3].

When magnesium deficiency develops, normal levels can often be restored by dietary modification. Foods rich in magnesium include wheat bran, pumpkin seeds, sunflower seeds, spinach, leafy greens, parsley, dill, carrots, soybeans, asparagus, peas, seaweed, raisins, mushrooms, fish, crab, shrimp, dark chocolate, and nuts [1].

Magnesium supplements are also widely available. These preparations differ not only in their chemical composition but also in their bioavailability [3].

Magnesium Balance in the Body

Magnesium is essential for maintaining normal physiological function. Magnesium deficiency (hypomagnesemia) is considerably more common than magnesium excess and may contribute to numerous health problems.

Insufficient magnesium increases the risk of cardiovascular disease, cardiac arrhythmias, blood pressure abnormalities, muscle cramps, and even certain malignancies. Even in otherwise healthy individuals, magnesium deficiency may contribute to disturbances of cardiac rhythm [4].

A case-control study involving more than 32,000 participants found that women with plasma magnesium concentrations below 0.82 mmol/L had a 1.34-fold higher risk of stroke, which was attributed to endothelial dysfunction and an increased tendency toward hypertension [5].

Magnesium deficiency has also been associated with chronic fatigue, drowsiness, and various emotional disturbances.

Common causes of hypomagnesemia include physical exhaustion, chronic stress, excessive alcohol consumption, inadequate dietary intake, vomiting, diarrhea, and malabsorption syndromes [1,4].

Large epidemiological studies conducted during the mid-20th century established magnesium as an essential component of the human diet.

According to WHO dietary recommendations, the daily magnesium intake should be approximately:

• Infants: 40–60 mg/day
• Children up to 15 years: 80–310 mg/day
• Adolescent boys and adult men: 350–400 mg/day
• Adolescent girls and adult women: 300–350 mg/day

Pregnant and breastfeeding women should consume an additional 100 mg/day of magnesium [1,6].

Magnesium and Cardiovascular Disease

Sudden cardiac death accounts for approximately half of all deaths related to ischemic heart disease.

Paradoxically, many of these individuals are not classified as being at high cardiovascular risk. Approximately 55% of men and 68% of women who die suddenly have neither been evaluated nor treated for cardiovascular disease [6].

Experimental studies have demonstrated that magnesium deficiency has proarrhythmic effects even in structurally normal hearts.

Magnesium exerts multiple beneficial effects on cardiac function. It suppresses abnormal automaticity, reduces myocardial cell membrane excitability, improves coronary blood flow, does not prolong myocardial repolarization, and helps prevent intracellular potassium depletion.

Magnesium is also essential for maintaining resting membrane potential, membrane stability, and normal myocardial excitability.

Numerous prospective epidemiological studies have demonstrated associations between magnesium deficiency and cardiovascular disease, particularly ventricular arrhythmias, sudden cardiac death, and overall mortality.

Hypomagnesemia is frequently accompanied by hypokalemia and prolongation of the QT interval on electrocardiography. Together, these abnormalities substantially increase the risk of ventricular arrhythmias [1,2].

A meta-analysis of seven large prospective studies also demonstrated a significant relationship between dietary magnesium intake and stroke risk. Increasing daily magnesium intake by more than 100 mg reduced the risk of ischemic stroke by approximately 8–9% [8].

Several mechanisms have been proposed to explain the protective effects of magnesium against stroke.

Magnesium deficiency is also associated with chronic cardiovascular disorders, including arterial hypertension, hyperlipidemia, and diabetes mellitus.

Its neuroprotective effects appear to be mediated primarily through blood pressure regulation.

Structural and functional vascular injury, endothelial dysfunction, oxidative stress, and vascular remodeling all contribute to the development and progression of hypertension.

Approximately 25% of patients with arterial hypertension are reported to have magnesium deficiency.

Published studies suggest that one important cause of hypomagnesemia in patients with hypertension is the use of diuretics, which increase urinary magnesium excretion [2].

In studies involving patients with heart failure treated with diuretics and cardiac glycosides, magnesium supplementation was associated with progressive improvements in intracellular magnesium concentrations and favorable cardiovascular effects [7,8,11].

Magnesium Citrate and Bioavailability

Comparative studies of different magnesium salts have demonstrated differences in absorption.

Measurements obtained 9 and 24 hours after administration showed that intracellular magnesium concentrations were higher in individuals receiving magnesium citrate than in those receiving magnesium oxide [3].

Summary

Large prospective clinical studies have demonstrated that magnesium deficiency is associated with an increased risk of stroke and sudden cardiac death, emphasizing the importance of adequate magnesium intake for maintaining cardiovascular health.

Clinical symptoms of hypomagnesemia may occur even when serum magnesium concentrations remain within the normal range.

For this reason, maintaining adequate magnesium intake through a magnesium-rich diet or appropriate supplementation is important.

Although studies comparing different magnesium salts have varied considerably in methodology, their conclusions have been relatively consistent. Organic magnesium salts exhibit greater solubility, resulting in better gastrointestinal absorption.

Among currently available magnesium preparations, magnesium citrate has consistently demonstrated superior bioavailability compared with magnesium oxide, making it one of the most suitable forms of magnesium supplementation according to available clinical evidence.

Prepared by Dr. E. Tamulevičiūtė-Prascienė

Lithuanian Doctor's Journal, No. 7