Several studies have reported that high
sodium (Na) intake increases not only urinary Na but also urinary
calcium (Ca), suggesting that high Na intake could be involved in the pathogenesis of
hypercalciuria. No research data are available on the relationship of Na intake to the prevalence of
hypercalciuria within the general population. Moreover, it is not clear if Na intake relates only to urinary Ca or also to other indices of Ca homeostasis, including intestinal Ca absorption. In the present paper, two distinct studies addressed these points using 24-hour urinary Na as an index of
salt intake in individuals on their habitual unrestricted free diet. Study 1 analyzed the relationship between 24-hour urinary Na and
hypercalciuria (24-hour urinary Ca > or = 7.5 mmol in men, > or = 6.25 mmol in women) in a population sample of 203 men and women, aged 20-59 years. Study 2 analyzed the relationship between 24-hour urinary Na and intestinal
strontium (Sr) absorption, used as an index of intestinal Ca absorption, urinary (24-hour and fasting) and plasma Ca, and plasma
parathyroid hormone in 36 healthy men and women, aged 18-65 years. Within the population sample (study 1), 24-hour urinary Na was directly and significantly correlated with prevalence of
hypercalciuria when controlling for gender, age, weight, and urinary
creatinine: the relationship was continuous and linear for urinary Na ranging between 40 and 200 mmol/24 h. In the 36 volunteers (study 2), 24-hour urinary Na was related to 24-hour and fasting urinary Ca (p < 0.001) but not to intestinal Sr absorption: the relationship between 24-hour urinary Na and urinary Ca (both 24 h and fasting) was also significant, controlling for other variables. The results indicate that in adults on their habitual diet, urinary Na, which reflects dietary
salt intake, correlates with the prevalence of
hypercalciuria independently of intestinal Ca absorption and mainly via renal mechanisms.