Magnesium is the second most abundant cation inside our cells. Most of it is found in the bones or muscles, with about 7% inside other cells and less than 1% outside our cells. Like potassium (the most abundant cation in the cells), blood levels will basically always be normal except for changes made by intravenous solutions that are out of balance.
Magnesium is vital for hundreds of metabolic reactions including:
- Required for ATP (energy for all cells).
- Required for DNA and RNA and making proteins.
- Required for bone structure.
- In cell membranes, it is needed for potassium (K) and calcium (Ca) transport.
- Nerve impulses and muscle contraction requires Mg.
- Cell signaling requires Mg-ATP and cyclic adenosine monophosphate (cAMP).
- Cell migration requires Ca and Mg, important in wound healing.
The absorption of magnesium can be reduced by high dose zinc supplements (over 100–150 mg/day), low protein diets (less than 30 grams a day), and high fiber diets.
SYMPTOMS OF DEFICIENCY
Deficiency severe enough to cause symptoms is rare. When you become magnesium deficient, (hypomagnesemia) the body also develops low calcium (hypocalcemia) which results in increased parathyroid hormone (PTH). This normalizes blood calcium, so only ongoing severe deficiency can lead to the symptoms of low Mg which really are also due to low calcium:
- Low Ca, low K, increased sodium, low PTH.
- Nausea, vomiting, and loss of appetite.
- Tremor, muscle spasms, tetany.
- Personality changes.
Deficiency is usually seen when there is a lack of absorption:
- Inflammatory bowel disease (Crohn’s).
- Malabsorption syndromes and surgical resection of bowel.
- Diabetes or long term diuretic use causing renal wasting.
- Older age due to lower intake and increased urinary loss.
In pregnancy, about 7% of women develop pre-eclampsia (high BP, protein in urine and edema) or eclampsia (the above plus seizures). Magnesium has long been the treatment that prevents seizures and death, by stopping the spasm of blood vessels in the brain and increasing blood flow. Migraines also seem to be caused by blood vessel spasms and are often helped by adequate magnesium intake.
Green vegetables, legumes, nuts and unrefined grains have the highest content of magnesium.
100% bran cereal (all bran) (1/2 cup) 129
Oat bran (½ cup dry) 96
Brown rice (1 cup cooked) 84
Spinach/ chard/ leafy greens (1/2 c) 75
Lima beans (1/2 c) 63
Nuts (1 ounce) 49
Banana (1) 34
Harder water will have some magnesium.
SAFETY AND TOXICITY
No side effects are reported from natural intake from food. When magnesium is used in laxatives, or high doses of supplements are used, the first sign is diarrhea. Those with kidney problems may not excrete magnesium adequately, and can develop high levels (hypermagnesemia).
Beyond diarrhea, the next effect of high Mg is low blood pressure (BP). It is probably the low BP (hypotension) that results in the symptoms of lethargy and confusion. In severe cases, the heart rhythms can be affected and cardiac arrest can occur.
TOLERABLE UPPER LIMITS
Children 1 – 3 65
Children 4 – 8 110
Age 9 – adults 350
The recommended daily allowance (RDA) for pregnancy and breastfeeding is 350–400, reflecting the importance of magnesium. Doses between 400 and 1000 mg are usually tolerated by adults, but moderation is wise.
If you are not eating enough high magnesium foods, or if you have migraines or are pregnant, consider an appropriate dose of magnesium as a supplement. Due to the closer interaction between Mg and Ca, it is generally recommended that these are supplemented together, and for proper calcium movement into bone, vitamin K2 is advisable when supplementing calcium.