Sodium, potassium, phosphorus, and magnesium

Abstract

Bone health is not a mononutrient issue; not only calcium and vitamin D but many other nutrients (sodium, potassium, phosphorus, and magnesium) are also known to affect the calcium economy and bone status. The contemporary Western diet is generally thought to contain more sodium than our hunter-gatherer ancestors would have consumed, and substantially less potassium. An increase in the filtered load of either sodium or calcium leads to increased clearance of both ions. In fact, urine calcium rises by from 1.0 mmol (40 mg) for every 100 mmol (2,300 mg) sodium ingested. Sodium intake accounts for most of the obligatory urinary loss of calcium from the body and if absorbed calcium is less than the amount needed to offset this loss then bone mass must suffer, particularly in postmenopausal women. Potassium is important to bone health because of its effects on the processes that maintain calcium homeostasis, particularly urinary calcium conservation and excretion. Foods high in potassium generally have an alkaline ash characteristic, including fruits and green and root vegetables which should be increased in the diet. A diet containing an amount of protein adequate for health will also contain adequate phosphorus. The RDA in the U.S. for phosphorus is 700 mg (23 mmol)/day for adults and median intakes for adults are above that level at all ages. Low food phosphorus intake and large calcium supplement doses along with osteoporosis treatments may lead to phosphorus deficiency. The richest dietary source of magnesium is legumes, followed by grains and root and green vegetables. More than 70 % of the adult population in the U.S. falls below recommended intakes of magnesium, but it is unclear whether this shortfall has skeletal consequences. Outside of certain special therapeutic or disease situations, the usually encountered variations in intakes of sodium, potassium, phosphorus, and magnesium are without major skeletal consequences.