Metabolism of vitamin D may be ineffective in people who are deficient in magnesium, suggest the authors of the review paper, a collaboration between the School of Dentistry at the University of Rwanda College of Medicine & Health Sciences and Harvard University.
Without sufficient magnesium, vitamin D can remain stored and inactive within the body, says the study which is published in The Journal of the American Osteopathic Association.
Poor magnesium status may therefore leave individuals vulnerable to vitamin D-related disorders such as bone disorders and cardiovascular disease. Inadequate magnesium may also increase the risk of vascular calcification, the scientists warned.
"By consuming an optimal amount of magnesium, one may be able to lower the risks of Vitamin D deficiency, and reduce the dependency on Vitamin D supplements," said study co-author Professor Mohammed Razzaque.
"People are taking Vitamin D supplements but don't realize how it gets metabolised. Without magnesium, Vitamin D is not really useful or safe," added Razzaque.
Mechanisms and synergy
Magnesium is key to enabling vitamin D to be transformed into a usable form within the body, explained the scientists.
The two-stage process within the liver and kidneys which converts vitamin D into its biologically active form 1,25-dihydroxyvitamin D (1,25[OH]2D) is a magnesium dependent process, the researchers elaborated. Similarly, the activity of the vitamin D binding protein, responsible for transport of the vitamin in the blood, is also dependent on magnesium.
Magnesium and vitamin D work together synergistically, the researchers noted. Patients with optimum magnesium levels require less Vitamin D supplementation to achieve sufficient vitamin D levels. In turn, adequate vitamin D levels promote magnesium absorption in the gut.
“Magnesium is an essential cofactor for vitamin D synthesis and activation and, in turn, can increase intestinal absorption of magnesium and establish a feed-forward loop to maintain its homeostasis,” commented Razzaque.
High prevalence of deficiency
In the U.S., the regular diet contains only around half the recommended daily allowance (RDA) for magnesium (310 milligrams/ day for women, 420 mg/d for men). Around 75% of the American population is estimated to have inadequate dietary intakes of magnesium, the researchers highlighted.
Magnesium status is low in populations who consume processed foods that are high in refined grains, fat, phosphate, and sugar, they added.
Magnesium is the fourth most abundant mineral in the human body after calcium, potassium, and sodium. Bones and teeth contain about 60% of magnesium in the body, with just under 40% consisting of intracellular stores. Only around 0.3% is present in serum.
Serum magnesium is therefore a poor predictor of magnesium status, the researchers explained. The body homeostatically maintains serum levels at expense of tissue and bone levels. Therefore, ‘latent’ magnesium deficiency can frequently go unnoticed.
“Even when the skeletal or intracellular magnesium content of soft tissue may be depleted, the circulating levels of magnesium could remain within the normal range because of its tight homeostatic control,” said Razzaque.
“Severely reduced tissue and bone magnesium content in the setting of normal serum magnesium levels has been termed ‘chronic latent magnesium deficit.’”
Sources of magnesium
Foods high in magnesium include almonds, bananas, beans, broccoli, brown rice, cashews, egg yolk, fish oil, flaxseed, green vegetables, milk, mushrooms, other nuts, oatmeal, pumpkin seeds, sesame seeds, soybeans, sunflower seeds, sweet corn, tofu, and whole grains.
Nevertheless, the magnesium content of various foods including vegetables has declined by an estimated 25-80% since 1950, said the researchers.
The increased use of pesticides and fertilisers (which affects soil content), together with the refining process of grains and oils which removes magnesium, are contributory factors to the reduced presence of the mineral in our diets.
“Magnesium consumption from natural foods has decreased in the past few decades, owing to industrialised agriculture and changes in dietary habits,” said the researchers.
Understanding of the role of magnesium in health and disease is rapidly evolving say the researchers.
“Further controlled studies should determine the dose of magnesium required for a particular clinical situation for reducing vitamin D–associated disorders.
A better understanding of how magnesium supplementation might reduce complications related to vitamin D deficiency would help improve patient care,” concluded Razzaque.
Source: The Journal of the American Osteopathic Association
Volume 118, issue 3, pages 181-189, doi: 10.7556/jaoa.2018.037
Role of Magnesium in Vitamin D Activation and Function
Authors: Anne Marie Uwitonze, Mohammed S. Razzaque