A good rule of thumb for healthy peoples’ reliable magnesium intake:   multiply your body weight in pounds by 3.  That’s a good estimate of the amount of milligrams magnesium per day you need to remain healthy.

The RDAs for Magnesium were published in 1997.  They used body weights of 133 lbs for adult women and 166 lbs for adult men.  Since 1997 research has found that magnesium requirement goes up with total body weight.  The current average USA adult body weights for women and men are higher that these values used in 1997.  So, the RDAs for magnesium are too low to accomplish their goal:  the amount of magnesium needed daily by healthy people to prevent any future magnesium deficit.

Updated Magnesium RDAs for updated average body weights of USA adults:

Age-Gender Group Revised magnesium RDA

for current avg body weight

Current Avg Body Weight USA adults
Women age 19-30 yrs 450 – 514 mg/day 168.5 lbs
Men age 19-30 yrs 542 – 620 mg/day 196 lbs
Women aged 31+ years 467 – 534 mg/day 168.5 lbs
Men aged 31+ years 575 – 657 mg/day 196 lbs

Chart for Traditional Magnesium & Calcium RDA Table:  The RDA (Recommended Dietary Allowance) is the amount of an essential nutrient that will meet the daily requirement for almost all (97.5%) HEALTHY individuals in any given gender and age-range group.  The current, published RDAs for both magnesium and calcium are printed in the chart below.  The REVISED magnesium RDAs for healthy adults is shown above.   (See Below for full explanation of RDA, DRI and AI.)

Age-Gender Group Magnesium RDA

Milligrams/day

Magnesium AI

Milligrams/day

Calcium AI

Milligrams/day

Calcium RDA

Milligrams/day

0 – 6 months 30 mg 200 mg
7 – 12 months 75 mg 260 mg
1 – 3 yrs 80 mg 700 mg
4 – 8 yrs 130 mg 1000 mg
Girls: 

9 – 13 yrs

14 – 18 yrs

240 mg

360 mg

1,300 mg

1,300 mg

Boys: 

9 – 13 yrs

14 – 18 yrs

240 mg

410 mg

1,300 mg

1,300 mg

Women:

19 – 30 yrs

31 – 50 yrs

51 – 70 yrs

Over 70 yrs

310 mg

320 mg

320 mg

320 mg

1,000 mg

1,000 mg

1,200 mg

1,200 mg

Men: 

19 – 30 yrs

31 – 50 yrs

51 – 70 yrs

Over 70 yrs

400 mg

420 mg

420 mg

420 mg

1,000 mg

1,000 mg

1,000 mg

1,200 mg

Pregnancy: 

aged 14 – 18 yrs

aged 19 – 30

aged 31 – 50

400 mg

350 mg

360 mg

1,300 mg

1,000 mg

1,000 mg

Lactation:

Aged 14 – 18 yrs

Aged 19 – 30

Aged 31 – 50

360 mg

310 mg

320 mg

1,300 mg

1,000 mg

1,000 mg

The above table lists the DRI’s (both AI’s and RDA’s for nutritional magnesium and nutritional calcium as determined by the Food and Nutrition Board, Institute of Medicine of the National Academy of Sciences. The revised 2010 values for Calcium are listed in the above chart. The Magnesium values were set in 1997.  The body weight revised magnesium RDAs above are from a recent study.

What does the RDA mean?

The RDA (Recommended Dietary Allowance) is the amount of an essential nutrient that will meet the daily requirement for almost all (97.5%) HEALTHY individuals in any given gender and age-range group.  Persons who are ill or have an “out of normal range” blood or blood pressure or cholesterol or other value DO NOT fall into this “HEALTHY” category, and most likely they need more Magnesium each day to not get in worse shape, nutritionally.

RDA’s are calculated from experimentally measured EAR or Estimated Average Requirement values.  An EAR or Estimated Average Requirement is the amount of a nutrient that will meet the daily requirement of about half of the HEALTHY people in a specified age-gender group.

When not enough studies have been done to determine a nutrient’s EAR, an RDA for that nutrient cannot be calculated.  In such cases, the AI or Adequate Intake is set, based upon scientific observations of a nutrient’s average intake by a group of HEALTHY persons.

Persons who are ill or have an “out of normal range” blood value DO NOT fall into this “HEALTHY” RDA category.

Can you take too much calcium?  An Upper Tolerable Limit of non-food Calcium has been set at 2,500 – 3,000 mg calcium for all age-gender groups above 1 yr. of age because too much calcium can lead to kidney stone formation, a combination of high blood calcium coupled with low kidney function (known as milk-alkali syndrome) and possible interference with other essential nutrients’ absorption and metabolism.  A high Calcium to Magnesium ratio has also been implicated in calcification of soft tissues and very recently to cancer.  In 2010 Vitamin D requirements were revised upward and some Calcium requirements were lowered.  Since Vitamin D enables Calcium absorption in the human GI tract, lowering the RDA’s for Calcium when Magnesium intakes are low and when Vitamin D requirements were revised upward was necessary.

In general, if one has adequate magnesium nutritional status, calcium supplements can help maximize bone mineralization, but when magnesium status is low, extra calcium may not be properly metabolized, manifesting low blood calcium that cannot be corrected with calcium supplements, only with magnesium supplements.

At the cellular level, a high intra-cellular calcium-to-magnesium ratio has been shown to be associated with all aspects of Metabolic Syndrome X which can manifest as Type 2 Diabetes.   [Resnick LM: Cellular calcium and magnesium metabolism in the pathophysiology and treatment of hypertension and related metabolic disorders. Am J Med 93:11S-20S, 1992. https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=1387762]  [Rosolova H, Mayer O, Jr., Reaven GM: Insulin-mediated glucose disposal is decreased in normal subjects with relatively low plasma magnesium concentrations. Metabolism 49:418-420, 2000. https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=10726923]

Whether this aspect of too much calcium in the face of too little magnesium in humans can be shown to be causal at the physiological level awaits appropriate investigation.

Can you take too much magnesium?  IN general, oral magnesium supplements are quite safe, especially when ingested by people with healthy kidney function.   Upper Tolerable Limits of non-food Magnesium have been set for the following age groups as the level of Magnesium supplement where mild diarrhea or gastric cramps appear in ANY individual of that gender-age group:

1 – 3 yrs:        65 mg magnesium

4 – 8 yrs:        110 mg magnesium

Above 8 yrs:     350 mg magnesium

It’s confusing that the tolerable upper limit for magnesium (350 mg) is lower than the RDA for several gender-age groups.  This occurs because the tolerable upper limit has been set at the level where ANY INDIVIDUAL experiences even mild stomach or intestinal distress.  Very high levels of oral magnesium (up to 1000 times higher than the 350 mg tolerable upper limit, and even higher) have been shown to be tolerated with no adverse effects; however, some individuals have gastro-intestinal cramping, distress or diarrhea when an oral magnesium dose as low as 350 mg (65 mg – 110 mg in some children) is ingested.  According to the definition of “Tolerable Upper Limit”, these few individuals’ reaction, no matter how mild, need to be the set point for nutritional magnesium’s tolerable upper limit.

What About Vitamin D?

Many recent reports show low serum vitamin D values being related to several health issues including bone health and heart health.  Magnesium is required for the biological activation of Vitamin D.  When Magnesium status is low, Serum Vitamin D levels remain low (Rude, 1985) as do serum Calcium and serum Potassium.   It remains to be shown whether recent reports on Vitamin D and health issues are truly due to low levels of vitamin D, low levels of magnesium or both.  Since serum magnesium measurement is not yet a standard clinical measurement, it is scientifically unwarranted to move forward with prescriptions of high levels of Vitamin D without knowledge of a patient’s Magnesium status and the further scientific elucidation of the complex interaction of these related nutrients.   In 2010, the Institute of Medicine revised the Calcium AI’s, converting several into RDA’s and lowering the amounts required for some age/gender groups.  At the same time they converted the AI’s for Vitamin D to RDA’s, doubling or even tripling the Vit D requirements (https://www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D/DRI-Values.aspx   Also, see Ross, A. C., J. E. Manson, et al. (2011). “The 2011 Report on Dietary Reference Intakes for Calcium and Vitamin D from the Institute of Medicine: What Clinicians Need to Know.” J Clin Endocrinol Metabhttps://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=21118827   and see also https://books.nap.edu/openbook.php?record_id=13050)

Rude, R. K., J. S. Adams, et al. (1985). “Low serum concentrations of 1,25-dihydroxyvitamin D in human magnesium deficiency.” J Clin Endocrinol Metab 61(5): 933-40. https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=3840173