CLINICAL

  NUTRITION

HAVE ENOUGH MINERALS?

THE ROLES OF MAGNESIUM AND MANGANESE IN SYSTEMIC AND EYE HEALTH

MOST PEOPLE are familiar with the need for vitamins to maintain health. Minerals are essential as well, yet often get overlooked when discussing optimal food and nutrient intake.

Here, I discuss two of these important minerals, magnesium and manganese, their optimal levels, roles in systemic and eye health and supplementation.

OPTIMAL LEVELS

The U.S. recommended daily allowance (USRDA) of magnesium for adults older than age 30 is 420mg for men and 320mg for women.

A variety of foods contain magnesium, including fortified cereals (about 100mg in ½ cup), brown rice, mackerel, spinach, nuts, seeds and blackstrap molasses.

Optimal levels of manganese have not been established. Adequate intake levels, based upon representative American diets, are 2.3mg for men and 1.8mg for women.

Food sources of manganese include brown rice, spinach, legumes, nuts and green and black varieties of tea.

SYSTEMIC HEALTH

Magnesium is involved in hundreds of metabolic and pathophysiologic reactions, including cell signaling, protein synthesis, food metabolism, energy production and structural functions in bone, cell membranes and chromosomes. In addition, glutathione, one of the most important antioxidants in the human body, requires magnesium for its synthesis.

Severe deficiency of magnesium is rare, but recent studies suggest that mild deficiency is quite common in the U.S. adult population. Of note: Long-term use proton pump inhibitors, such as Esomeprazole (Nexium, AstraZeneca), which are intended for short-term relief of gastro esophageal reflux disease, deplete magnesium stores. Magnesium deficiency is linked to insulin resistance, metabolic syndrome, depression, migraine headache and osteoporosis.

A low amount of magnesium is also associated with all known cardiovascular risk factors, including hypertension and hypercholesterolemia. With the growing use of calcium supplements to increase bone density, an overall calcium-to-magnesium imbalance is increasing, and this imbalance may be the reason many studies suggest that calcium supplements increase the risk of heart disease.

Those at a particular high risk of magnesium deficiency have malabsorption from the gastrointestinal (GI) tract due to inflammation or bariatric surgery, increased urinary excretion of magnesium that can be caused by diuretic use or diabetes; chronic alcoholism (typically poor dietary intake, GI problems and increased urinary loss of minerals) and tend to be older.

Manganese plays an important role in many physiologic processes, including bone development, wound healing and numerous enzymatic reactions. Also, manganese superoxide dismutase (MnSOD, or SOD-2) is the primary antioxidant in mitochondria, the energy producers — and, therefore, free radical generators — of cells. Several diseases have been associated with low manganese levels, including osteoporosis, diabetes and epilepsy.

EYE HEALTH

Patients with diabetic retinopathy have significantly lower levels of magnesium than patients with diabetes, but without retinopathy, a recent study revealed. Magnesium deficiency is also a proposed factor in cataract formation, as the mineral is critical to several antioxidant pathways thought to maintain clarity of the lens. Further, low magnesium levels may contribute to primary vascular dysregulation, which is, in turn, thought to be one non-IOP-dependent factor in the pathogenesis of primary open angle glaucoma (POAG).

With regard to manganese, population studies have shown an association between low manganese levels and a high prevalence of glaucoma. Also, genetic variations resulting in reduced levels of MnSOD are associated with a high incidence of glaucoma and other neurodegenerative diseases, such as Alzheimer’s disease. This seems to add more weight to the growing body of evidence regarding non-IOP mechanisms as at least a partial contributor to the pathogenesis of POAG, underscoring the importance of this mineral in reducing oxidative stress at the subcellular level.

SUPPLEMENTATION

Most multivitamin/mineral supplements contain 100mg or less of magnesium. In addition to oral supplements, transdermal absorption of magnesium is possible with topical oil applications or an old-fashioned bath in Epsom salt (magnesium sulfate). These are often appealing options for patients.

When considering supplementation, exercise caution in patients who have renal impairment, as they are unable to excrete magnesium efficiently. Further, magnesium has several drug interactions, including over-the-counter antacids, several antibiotics (aminoglycosides, fluoroquinolones and tetracyclines) and metformin, that should be noted prior to recommending higher than usual doses. Of note: Over supplementation in healthy individuals is likely to cause diarrhea, but at very high levels can also cause several adverse effects, including hypotension. Therefore, should a patient present with these adverse effects, be sure to ask about magnesium supplementation.

Manganese is often an ingredient in good quality multivitamin/mineral supplements. If in doubt, check the labels of the products you recommend most often. OM

KIMBERLY K. REED, O.D., F.A.A.O., is a professor at the NOVA Southeastern University College of Optometry in Fort Lauderdale, Fla., a member of the Ocular Nutrition Society and author of numerous articles on ocular nutrition, disease and pharmacology. She is also a frequent continuing education lecturer. To comment on this column, email Dr. Reed at Kimreed@nova.edu, or visit tinyurl.com/OMcomment to comment on this article.