Upper Tolerable Limits of Magnesium Intake

Reference from the joint report of FAO/WHO expert consultation on Human Vitamins and Minerals verbatim.

63. Food and Nutrition Board, Institute of Medicine. 1997. Dietary reference intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Flouride. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Washington D.C., National Academy Press.

Magnesium from dietary sources is relatively innocuous. Contamination of food or watersupplies with magnesium salt has been known to cause hypermagnesemia, nausea, hypotension, and diarrhoea. Intakes of 380 mg magnesium as magnesium chloride have produced such signs in women. Upper limits of 65 mg for children ages 1–3 years, 110 mg for 4–10 years, and 350 mg for adolescents and adults are suggested as tolerable limits for the content of soluble magnesium in foods and drinking water (63).

Relationships to previous estimates

64. Health and Welfare Canada. 1992. Nutrition Recommendations: Health and Welfare, Canada. Report of the Scientific Review Committee, Ottawa, Supply and Services, Canada.

The recommended intakes for infants ages 0–6 months take account of differences in the physiologic availability of magnesium from maternal milk as compared with infant formulas or solid foods. With the exception of the Canadian RNI estimates, which are 20 mg/day for ages 0–4 months and 32 mg/day for ages 5–12 months (64), other national estimates recommend intakes as RDAs or RNIs which substantially exceed the capacity of the lactating mother to supply magnesium for her offspring. 

Recommendations for other ages are based subjectively on the absence of any evidence that magnesium deficiency of nutritional origin has occurred after consumption of a range of diets sometimes supplying considerably less than the US RDA or the UK RNI recommendations based on estimates of average magnesium requirements of 3.4–7 mg/kg body weight.

The recommendations submitted herewith assume that demands for magnesium plus a margin of approximately 20 percent (to allow for methodologic variability) are probably met by allowing approximately 3.5–5 mg/kg from pre-adolescence to maturity. This assumption yields estimates virtually identical to those for Canada. Expressed as magnesium allowance (in milligrams) divided by energy allowance (in kilocalories) (the latter based upon energy recommendations from UK estimates (21), all the recommendations of Table 46 exceed the provisionally estimated critical minimum ratio of 0.02.

It is appreciated that magnesium demand probably declines in late adulthood as requirements for growth diminish. However, it is reasonable to expect that the efficiency with which magnesium is absorbed declines in elderly subjects. It may well be that the recommendations are overgenerous for elderly subjects, but data are not sufficient to support a more extensive reduction than that indicated.