Reducing dietary intake of calcium has historically been targeted as a means of managing hypercalciuria. Recommendations for dietary calcium restriction were common for patients with hypercalciuria and for calcium stone formers. Although higher dietary calcium intake can increase intestinal absorption of calcium and subsequently increase urinary calcium excretion, calcium restriction does not appear to reduce the risk of stone formation. Large observational studies have, in fact, shown a significant inverse relationship between dietary calcium intake and risk of kidney stones, with a 34 % increased risk in young men with low calcium intake and similar results for young women and older women [1]. This may be due to a resultant increase of free oxalate absorption from the intestine with a low intake of oxalate-binding calcium. Additionally, dairy products, the primary source of dietary calcium, may offer protection against kidney stones related to other inhibitory factors of nephrolithiasis such as dietary potassium.

Patients with idiopathic hypercalciuria do not see reductions in urinary calcium excretion equal to the reduction in calcium ingested when placed on a restricted calcium diet [2]. This suggests an increase in bone resorption of calcium. Therefore, finding other ways to reduce urinary calcium concentration is warranted for protection of bone density as well as for stone prevention. Calcium supplementation has been observed to increase urinary calcium excretion, though the effect varies related to timing and dosage. For example, calcium supplements ingested without food and thus in the absence of its potential intestinal binders, such as oxalate and phytate, lead to greater intestinal calcium absorption and urinary excretion than when supplements are consumed at meals [1].

In light of the lack of evidence for stone prevention through calcium restriction and the risk of bone demineralization, the consensus recommendation for stone prevention is a moderate intake of dietary calcium consistent with the Dietary Reference Intakes for life stage and gender groups (1,000–1,300 mg for individuals from 9 years old through adulthood or approximately 3–4 servings of calcium-rich foods per day). If calcium supplements are needed to reach total intake recommendations, they should be taken with or shortly after meals and only in the dosage required to bring total calcium intake to goal.

Dietary sodium is a contributor to hypercalciuria related to sodium’s expansion of extracellular volume and sodium ion competition with calcium in the renal tubule. There is a 25–40 mg increase in urinary calcium for every 100 mEq increase (2,300 mg or the amount in one teaspoon or packet of salt) in dietary sodium intake per day [3]. Excretion of urinary calcium has been demonstrated to vary directly with changes in dietary sodium in kidney stone-forming patients [4]. In addition, lower bone density has been observed in stone formers with high sodium diets [5]. It is therefore worthwhile to advise these patients to reduce their intake of dietary sodium if it is high and if it is thought to contribute to excessive calciuria.

Recommendations to lower sodium intake are based ideally on an assessment that identifies a patient’s highest sodium contributors as well as those foods that contribute significantly to total sodium intake due to frequent consumption [6]. The American Heart Association targets bread as the top dietary contributor to American sodium intake. This is mainly due to the high frequency of bread intake in the typical American diet rather than the moderate sodium content of most bread servings.

Reducing sodium intake to 1,500–2,300 mg per day is desirable. This range is the recommendation from the 2010 Dietary Guidelines for Americans, the upper value being the daily sodium recommendation for healthy young adults and the lower being the target for those over age 50, African Americans, those with hypertension or with other risk factors [7].

Medical nutrition therapy provided by a registered dietitian nutritionist is valuable for guiding patients who need dietary sodium reduction for better stone prevention. Many patients will claim that they do not eat a lot of salt, but dietary assessment can help them understand their sodium intake beyond the salt shaker.