Magnesium and you-Part II

Blood magnesium levels are a poor barometer for true body (intracellular) magnesium.

Only 1% of the body’s magnesium is in the blood, the remaining 99% stored in various body tissues, particularly bone and muscle. If blood magnesium is low, cellular magnesium levels are indeed low—very low.

If blood magnesium is normal, cellular or tissue levels of magnesium may still be low. Unfortunately, tissue magnesium levels are not easy to obtain in living, breathing humans. In all practicality, a blood magnesium test only helps if it’s low, while normal levels don’t necessarily mean anything and may provide false reassurance.

Short of performing a biopsy to measure tissue magnesium levels, several signs provide a tip-off that magnesium may be low:

Heart arrhythmias—Having any sort of heart rhythm disorder should cause you to question whether magnesium levels in your body are adequate, since low magnesium levels trigger abnormal heart rhythms. In fact, in the hospital we give intravenous magnesium to quiet down abnormal rhythms.
Low potassium— Low magnesium commonly accompanies low potassium. Potassium is another electrolyte depleted by diuretic use and is commonly deficient in many conditions (e.g., excessive alcohol use, hypertension, loss from malabsorption or diarrhea). Like magnesium, potassium may not be fully replenished by modern diets.
Muscle cramps— Magnesium regulates muscle contraction. Leg cramps, or “charlie-horses”, painful vise-like cramps in calves, fingers, or other muscles, are a common symptom of magnesium deficiency. (Leg cramps that occur with physical activity, such as walking, are usually due to atherosclerotic blockages in the leg or abdominal arteries, not low magnesium.)
Migraine headaches—Reflective of magnesium’s role in regulating blood vessel tone, low magnesium can trigger vascular spasm in the blood vessels of the brain. In some emergency rooms, they will actually administer intravenous magnesium to break a migraine.
• Metabolic syndrome—Magnesium plays a fundamental role in regulating insulin responses. Metabolic syndrome (low HDL, high triglycerides, small LDL, high blood pressure, increased blood sugar, excessive abdominal fat, etc.) is triggered by insulin responses gone awry and is clearly linked to low magnesium levels.

The absence of any of these tell-tale signs does not necessarily mean that tissue levels of magnesium are normal.

Then how do you really know? There really is no easy, available method to gauge body magnesium. As a practical solution, we therefore have aimed for maintaining serum levels of >2.1 mg/dl or RBC magnesium (a surrogate for tissue levels) of >6.0 mg/dl. (Going too high is not good either, so occasional monitoring really helps. However, I've only seen this once in a psychotic woman who drank ungodly amounts of magnesium-containing antacids for no apparent reason; she almost ended up on a respirator due to respiratory suppression by the magnesium level of 11 mg/dl!)

In all practicality, because of magnesium’s crucial role in health, its widespread deficiency in Americans, and the growing depletion of magnesium in water, supplemental magnesium is necessary for nearly everyone to ensure healthy levels.

More on magnesium to come.

Comments (17) -

  • Jenny

    5/25/2009 1:49:21 PM |

    Most of the symptoms you describe will start to occur in people who did not have them before, if they embark on rigid low carb diets--20 grams a day or less.

    This is another reason why, though it isn't fashionable, it is healthier to cut carbs gradually, a meal at a time, rather than all at once in a way that causes a diuretic crisis.

    But dieters like the extreme method as they lose up to 10 lbs the first week of the extreme low carb diets and feel like they accomplished something. Of course, it all comes back the day they eat one meal with carbs.

  • mrezzu

    5/25/2009 3:43:38 PM |

    Though magnesium is deficient in most of the Americans ,I don't think that supplementary magnesium can be recommended for everybody. It should be given with caution , taking its side effects into consideration. Fruits that are rich in magnesium should be recommended indiscriminately.

  • Ed

    5/25/2009 10:17:25 PM |

    To paraphrase what you are saying:

    1) If blood magnesium is low, then tissue magnesium is low

    2) If blood magnesium is normal, then tissue magnesium is either low or normal

    3) If blood magnesium is high, then tissue magnesium is high.

    If I am paraphrasing you correctly, then it sounds like what you could do is supplement magnesium until blood levels go high, then back off.

    Does ZRT offer a magnesium test? Searching the site, it looks like it doesn't. Sounds like this may be tough as a DIY project.

    The US RDA for magnesium is 400mg/day. Is that enough? How the heck would you get 400mg/day of magnesium in water. I probably drink 2-4 cups of water/day. That sounds like a lot of dissolved magnesium. I'm no expert though...

    Do lectins (from grains or legumes) bind magnesium? A cursory google search suggests "yes."

  • Nameless

    5/26/2009 3:51:30 AM |

    Interesting that Dr. Davis mentions specific RBC values to shoot for, as I was always unsure what was optimal. My own value came back at 5.3, so maybe I should take a bit more magnesium.

    General questions:

    Have you noticed improved lipids in any of your patients once they reached 6.0+  magnesium RBC?

    Besides calcium possibly being not absorbed as well, are there any other mineral concerns when taking magnesium?

    What form of magnesium do you recommend?

    And are there any intracelluar mag tests, or other magnesium tests that show greater accuracy? I have read a mag loading test is actually the most accurate, but it sounds like a major pain to get done.

  • Tim TerlegÃ¥rd

    5/26/2009 8:12:17 AM |

    What do you think about hair mineral analysis? Is it of no use at all or is it just bad for measuring magnesium?

    I had a hair mineral analysis once. It showed I had normal levels of everything. I'm pretty sure I had low levels of zinc though, because my atopic dermatitis vanished when supplementing with zinc.

  • Dr. William Davis

    5/26/2009 11:47:37 AM |

    Yes, Ed. Well said.

    No, ZRT does not offer a test for magnesium presently.

    A discussion of how much and what form to come in future.

  • SnowDog

    5/26/2009 12:46:12 PM |

    Jenny, I disagree. I've been eating less than 20gs carbs per day for 9 months, and feel better than I have in my entire life. I've also lost 60 lbs. That certainly won't come back with one high-carb meal. I had been trying to lose weight for 20 years, and was amazed at how rapidly weight dropped when I cut back on the carbs.

  • ethyl d

    5/26/2009 5:16:31 PM |

    I had the interesting experience of adding a magnesium supplement last year, just to see if doing so improved how I feel, and I got episodes of tachycardia after I started it. I stopped taking it, the rapid heart beats stopped, and then I tried magnesium tablets a few months later again, with the racing heart beats coming back. So no magnesium supplements for me.

  • Anonymous

    5/26/2009 6:03:28 PM |

    there is a controversy how best to get the body use of magnesium ,most agree that magnesium , glyconate/citrate is the best form ,other believe to use only a topical form on the skin rather then a capsule ,does anybody have expiriance in comparison one over the other?

  • Nameless

    5/27/2009 2:19:02 AM |

    From what I've read, the glycinate (Albion) form is one of the best, with Biotron (soy/rice chelate) in the same ballpark. Orotate is also considered very good.

    Malate/Taurate is considered decent too. And then Citrate. Citrate is very affordable, but I have some concern there regarding increased aluminum absorption, as shown by  some studies testing calcium citrate.

    And I really doubt much magnesium  would be absorbed topically.

  • Leslie

    5/27/2009 4:15:14 PM |

    @ Nameless:  Of course it's absorbed through the skin, that's the benefit of an Epsom Salt bath.

  • Nameless

    5/27/2009 11:17:51 PM |

    There is probably some magnesium absorption through the skin, yes, but oral supplements would give better results (at least to be best of my knowledge).

    Here is an epsom salt study --

    Which showed greater absorption than I expected. Although it was sponsored by the epsom salt council, so perhaps take the study with a grain of salt...

  • Hennie

    5/28/2009 5:21:28 AM |

    Thanks Dr. Davis for your insight on this important subject of magnesium.  
    There is an old, very interesting book that was published in the early 1950's by well known biochemist and farmer, Andre Voisin.  He taught veterinary science in France and was an expert in soil, health and nutrition.  The book is about magnesium deficiency in cattle.  The title is Grass Tetany and the entire book can be read free online.
    I found this book to be fascinating and wonder how this compares to humans.
    For example I read  in chapter 15“Magnesium deficiency leads to deposits of calcium in the various tissues: heart, liver, kidney, etc.”

    Another excellent book is by Dr. Jonathan V. Wright, M.D. “Why Stomach Acid is Good for You.”  Without sufficient stomach acid minerals and other nutrients cannot be optimally utilized. This can be a problem as we age.

  • Anonymous

    5/28/2009 12:23:25 PM |

    Tissue magnesium levels can be measured in RBCs. Just order an RBC magnesium level. It can be done through Quest, doesn't even need to be a specialty lab.

  • buy jeans

    11/3/2010 7:36:30 PM |

    In all practicality, because of magnesium’s crucial role in health, its widespread deficiency in Americans, and the growing depletion of magnesium in water, supplemental magnesium is necessary for nearly everyone to ensure healthy levels.

  • Joan

    11/29/2011 7:48:37 PM |

    I'm 6 weeks into no wheat and basically have gone low carb (no wheat, very little corn, rice, potatoes).  I'm increasingly getting more and more migraine auras, almost on a daily basis.  In the past I would have a migraine maybe once a year.  I've started supplementing with Mg-L-threonate which helps.  My question is - how much?  Should I go to my doctor and have all of my electrolytes checked?  Thanks.