Extra Magnesium Needed for High-Dose Vitamin D Supplementation

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There are only a few major books on magnesium, and the first one, The Magnesium Factor, was written by Mildred Seelig, MD, MPH.

Those familiar with Dr. Seelig may be unaware that she was not only an expert on magnesium, but she was also very knowledgeable about vitamin D. More specifically, she understood the dangers of vitamin D megadoses, i.e., too much calcium: hypercalcemia.

For example, she wrote an article on it for Clinical Pediatrics in 1970: “Are American Children Still Getting an Excess of Vitamin D?”

Increase of one requires increase of the other(s)?

In her magnesium book there is a section, which isn’t noted in the index, entitled “High-Dose Vitamin D.”

Vitamin D is necessary for calcium absorption. When vitamin D levels are low, not much calcium is absorbed from the intestines into the bloodstream, even if there is plenty of calcium in the diet. However, doses of vitamin D higher than the amount necessary to achieve normal calcium levels can have negative effects.

If magnesium status is low or sub-optimal and vitamin D is very high, and especially if calcium is also high, calcium absorption can be high enough to make the magnesium deficiency worse and to worsen the risk of calcium moving abnormally into cells and soft tissues, including those of the heart and arteries.

Like most nutrients, calcium, phosphorus, and vitamin D have a range of optimal intakes. An intake below this range means deficit; an intake above it means that the otherwise beneficial nutrient can become toxic.

If you are low in magnesium, it is easier for calcium, phosphorus and vitamin D to become toxic or, conversely, for resistance to vitamin D to develop.

We are not suggesting that you forego calcium supplements to prevent osteoporosis, to do without phosphorus and vitamin D, or to avoid vitamin D-fortified milk. We are suggesting you get adequate magnesium so that a high level of these nutrients will not exacerbate a deficiency or sub-optimal magnesium intake.

If you are told that you need unusually high doses of any vitamin, keep in mind that magnesium activates vitamin D, and that lower doses of vitamin D are needed when inadequate magnesium is corrected.[1]

Naturopath’s experience

A blog post about the safety of vitamin D resulted in a long discussion about nutrients.

“I’ve been able to prevent and/or reverse the exact same symptoms [reactions to vitamin D] that you are finding,” wrote Kerri Knox, RN, “by always dosing with magnesium at the same time as giving the vitamin D.

“If someone has these reactions, I’ll have them stop the vitamin D and do an intensive magnesium replenishment program for about a week before they start taking it again and, voila, no more issues with chest pain, anxiety, insomnia, jitteryness, kidney stones, etc…. I find these symptoms are an ‘induced’ magnesium deficiency in those who are already ‘borderline’ magnesium deficient.

“I always try to tell people that vitamins are not drugs and don’t work alone in a vacuum. They work together as cofactors in relationships that science may not understand yet. This seems like a perfect example of those relationships.”[2]

“We need to be balanced as well as adequate,” says Dr. Andrea Rosanoff, co-author of The Magnesium Factor. “Our magnesium requirement is really higher than the RDA. The RDA as it is currently set does not account for the weight gains that we’ve had. It does not account for the high calcium intakes that we have. And it doesn’t account for the high levels of stress that we experience.”[3]

Mineral balance in fibromyalgia patients

Dr. Anna Hoeck says she has successfully treated patients with chronic fatigue syndrome.

[A] minority of patients did not recover. One cause of treatment failure is supposed to origin[ate] from my former ignorance about the probably high impact of concomitant calcium and phosphate deficiency which is supposed to be a major cause for vitamin D resistance. Meanwhile I speculate if my first patient would have done better, if calcium and phosphate would have been substituted from the very beginning. Maybe, fibromyalgia and osteoporosis would have been prevented. At that early time of my detection, I feared too much to induce extra-osseous calcification. I did not yet know that adequate calcium, phosphate and vitamin D3 will counteract extra-osseous calcification.[4]

Absorption and retention ranges

Seelig believes patient treatment is even more complex based on diverse responses to magnesium. “The people in balance studies,” she wrote, “absorbed anywhere from 0 to 90 percent of the magnesium in the food they ate. This is a huge range. They excreted anywhere from 8% to 78% of the ingested magnesium… Another huge range…. Because the absorption and excretion of magnesium are so important in meeting our needs, genetic variations in intestinal and kidney function are important in controlling magnesium metabolism.”[5]

Dr. Holick on magnesium

One person said to him: “I have heard that it is important to take magnesium along with vitamin D. Is there any reason for this?”

“There is no need to take magnesium along with vitamin D,” Holick replied. “Vitamin D is efficiently absorbed with or without magnesium.”[6]

Vitamin K2

Hoeck said some of her patients “probably would have needed additional vitamin K substitution, because vitamin K is described to prevent renal calcium loss.”[7]

Most of the online discussion about safely supplementing with high doses of vitamin D seems to be centered on adding K2 as opposed to magnesium. At the end of her book, Vitamin K2 and the Calcium Paradox, Kate Rheaume-Bleue says:

Magnesium is essential for the absorption and metabolism of vitamin D. Magnesium deficiency, thought by many health experts to be common, impairs vitamin D metabolism. In particular, a lack of magnesium limits the conversion of vitamin D to active, hormonal form. To reap the full benefits of vitamin D, and by extension vitamins D and A, you need magnesium.[8]

Excess calcium

The second major book on magnesium is The Magnesium Miracle by Dr. Carolyn Dean. “Too much calcium automatically creates a magnesium deficiency,” says Dean. “Americans in general have a high calcium-to-magnesium ratio in their diet and consequently in their bodies.” The U.S. ratio in one study, she said, was 3.5:1.[9] She then noted that Dr. Seelig predicted it would rise to 6:1.

At the end of her book she agrees with Seelig, Rheaume-Bleue and Knox. “You should increase magnesium intake,” Dean wrote, “when you consume more phosphorus and vitamin D.”[10]

The conclusion of a 2018 study was: “Our findings suggest that optimal magnesium status may be important for optimizing 25(OH)D status.”

Now the open questions are: How much magnesium does someone need? How well do they absorb it? And how effectively do they keep it?

Studies on vitamin D and magnesium

Karen Howard, Executive Director of Organic & Natural Health Association, advises Congress and state legislatures. In 2020 she said a study was being done looking at the interaction of vitamin D with magnesium and Omega 3. Commenting on preliminary results, she said: “50% of those who are low in magnesium will need 146% more Vitamin D to get it [their level] to 40.”[11]

How much more Mg do they need?


Magnesium bisglycinate has become popular for enabling larger-than-usual doses without typical side effects. Even more Mg can be absorbed by multiple smaller doses during a day instead of a single supplement daily. Every four hours or breakfast, lunch, dinner, and just before you go to sleep you might be able to take the same dose, e.g., 50-100 mg. If you divide daily vitamin D doses into, say, three, you could always take Mg at the same time.

  1. Mildred Seelig, The Magnesium Factor, 2003, pp. 260-261.
  2. https://www.westonaprice.org/is-vitamin-d-safe-still-depends-on-vitamins-a-and-k-testimonials-and-a-human-study/ [Nov. 5, 2021].
  3. https://youtu.be/4sfXLJdIJhc?t=1943 [Nov. 5, 2021].
  4. Hoeck, A. (2017). May Fibromyalgia be caused by Long-Standing Vitamin D Deficiency? Journal of Chronic Diseases and Management. https://www.jscimedcentral.com/ChronicDiseases/chronicdiseases-2-1007.pdf [Nov. 5, 2021].
  5. Seelig, pp. 194-195.
  6. Michael Holick, The Vitamin D Solution, p. 251.
  7. Hoeck.
  8. Kate Rheaume-Bleue, Vitamin K2 and the Calcium Paradox: How a Little-Known Vitamin Could Save Your Life, 2013, p. 234.
  9. Carolyn Dean, The Magnesium Miracle, Ballantine: New York, 2007, p. 122.
  10. Ibid, p. 252.
  11. Benson D. (2020). Conversation With Karen Howard: Vitamin D. Integrative medicine (Encinitas, Calif.), 19(4), 40–44.

Magnesium deficiency with phosphate and vitamin D excesses; role in pediatric cardiovascular disease? Cardiovasc Med 3:637-650.

Selected works of Dr. Mildred Seelig

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