mean of 237 ± 62 mg (9.9 ± 2.6 mmol)/day, while Hispanic females consumed a mean of 232 ± 71 mg (9.7 ± 3.0 mmol)/day (Pluckebaum and Chavez, 1994).
Magnesium is ubiquitous in foods, but the magnesium content of foods varies substantially. Because chlorophyll is the magnesium chelate of porphyrin, green leafy vegetables are rich in magnesium. Foods such as unpolished grains and nuts also have high magnesium content, whereas meats, starches, and milk are more intermediate. Analyses from the 1989 Total Diet Study of the U.S. Food and Drug Administration indicated that approximately 45 percent of dietary magnesium was obtained from vegetables, fruits, grains, and nuts, whereas about 29 percent was obtained from milk, meat, and eggs (Pennington and Young, 1991). Refined foods generally have the lowest magnesium content. With the increased consumption of refined and/or processed foods, dietary magnesium intake in the United States appears to have decreased over the years (Marier, 1986). Total magnesium intake is usually dependent on caloric intake, which explains the higher intake levels seen in the young and in adult males and the lower levels seen in women and in the elderly.
Water is a variable source of intake; typically, water with increased “hardness” has a higher concentration of magnesium salts. Since this varies depending on the area from which water comes, much like fluoride, and the manner in which it is stored, magnesium intake from water is usually not estimated except in controlled diet studies. This omission may lead to underestimating total intake and its variability.
Based on a national survey in 1986, 14 percent of men and 17 percent of women in the United States took supplements containing magnesium (Moss et al., 1989). Approximately 8 percent of young children (2 to 6 years of age) used magnesium-containing supplements. Women and men who use magnesium supplements took similar doses, about 100 mg (4.2 mmol)/day, although the ninety-fifth percentile of intake was somewhat higher for women, 400 mg (16.7 mmol)/day, than for men, who were taking 350 mg (14.6 mmol)/day. Children who took magnesium had a median daily intake of 23 mg (1 mmol) and a ninety-fifth percentile daily supplemental intake of 117 mg (4.9 mmol).