Chemistry Reference
In-Depth Information
reactions involve synthesis of deoxyribonucleic acid (DNA) and ribonucleic
acid (RNA), protein and, adenylate cyclase glycolysis, cellular energy pro-
duction and storage and preservation of cellular electrolyte composition.
Magnesium regulates intracellular calcium and potassium at the cell mem-
brane level, and thus is a controlling factor in nerve transmission, skeletal and
smooth muscle contraction, cardiac excitability, vasomotor tone, blood pres-
sure and bone turnover.
Severe magnesium deficiency, usually the result of dysfunctional states
causing malabsorption or excessive excretion, results in numerous signs and
symptoms including loss of appetite, nausea, vomiting, fatigue and weakness.
As the deficiency becomes more severe, numbness, tingling, muscle contrac-
tions and cramps, seizures, personality changes and coronary spasms (angina
pectoris) occur. A chronic low intake of magnesium may result in cardiovas-
cular dysfunctions such as hypertension and dysrhythmias, bone loss leading
osteoporosis, and insulin resistance and impaired insulin secretion leading to
diabetes mellitus. The major effect of excessive magnesium intake is diarrhea
(Food and Nutrition Board: Institute of Medicine, 1997; Volpe, 2006), but
nausea and abdominal cramping may also occur. High serum magnesium
(hypermagnesmia) causing more severe magnesium toxicity signs is most
commonly associated with the combination of impaired renal function and
high intakes of non-food sources of magnesium such as magnesium-contain-
ing laxatives and antacids. Signs of hypermagnesmia include muscle weak-
ness, extremely low blood pressure, difficulty in breathing, irregular heartbeat
and change in mental status.
The FNB (Food and Nutrition Board: Institute of Medicine, 1997)
found no functional criteria on which to base an RDA for infants. Thus,
they set an AI for magnesium that reflects the mean intake of infants fed
principally with human milk (Table 10.2). An RDA for magnesium was set
for children aged 1-3 yr by interpolating data from other age groups. Data
from the US National Health and Nutrition Examination Survey
(NHANES) 2001-2002 indicated that the majority of people consumed less
than the EAR for magnesium (Moshfegh et al., 2005). For example, 64% of
women aged 51-70 yr did not attain the magnesium EAR. A recent analysis
of primary magnesium balance data from tightly controlled metabolic feed-
ing studies indicates a presumptive EAR of 165 mg/d and a presumptive RDA
of 237 mg/d for magnesium for men and women (Hunt and Johnson, 2006).
The adult human body contains about 25 g (1028 mmol) of magnesium,
which is about equally divided between bone and soft tissue (Volpe, 2006).
Less than 1% of the total body magnesium is in blood. Approximately one-
third of skeletal magnesium is exchangeable, and acts as a pool for maintain-
ing normal concentrations of extracellular magnesium. Thus, extracellular
magnesium stays relatively constant, even if skeletal and intracellular levels
