In hot climates the increase in daily urinary excretion of calcium in non-acclimatised subjects was explained by the action of ultraviolet rays that stimulate the production of vitamin D3 with consequent increased intestinal absorption of calcium. In regions with temperate climates, seasonal variations in calcium excretion were also recorded during the summer months and corresponded with increased plasma levels of vitamin D3. Conversely, it has been observed that levels of circulating vitamin D3 in the Saudi Arabian population are normal. One must therefore suggest mechanisms for adaptation in regions constantly exposed to solar radiation. Cheap generic drugs online
Idiopathic calcium renal stone disease
Mean urinary calcium has been found to be higher in patients with idiopathic calcium renal stone disease compared with controls. This relation has been showed in men and women, in children and adults, and in different countries (Table I). Furthermore, it has been demonstrated that, after adjusting for other urinary risk factors, daily urinary calcium output is an independent risk factor for calcium kidney stone formation. The risk for stone formation in men with daily urinary calcium output greater than 300 mg is four-fold higher than in men excreting less than 150 mg/day, whereas for the same values the risk in women is twice higher. According to the commonly accepted criteria, about 50% of patients with calcium oxalate stones are hypercalciuric. However, comparison of renal stone formers with recurrences and those with no further stone episodes showed that recurrence was not significantly influenced by an increased value of urinary calcium.
Hypertension is often associated with increased urinary calcium excretion. Borghi et al. demonstrated that daily urinary calcium output was significantly higher in healthy controls (202±93 mg/24 hour) than in essential hypertensive subjects (275±112 mg/24 hour)). Urinary calcium excretion remained higher in hypertensive subjects even if corrected for body mass index. A 20 mmHg higher systolic blood pressure predicts a 0.28 mmol higher urinary calcium.
Some Authors have pointed out that body mass index is significantly correlated with urinary calcium excretion. A retrospective review (54) of a large data base on urinary stones was recently performed in order to determine the effect of obesity on stone recurrence. Obese patients represented 3.8% of the males and 12.6% of the females. Obesity alone increased slightly the risk of recurrence in male obese (>120 kg) patients, but not in obese (>100 kg) females. Obese subjects had increased urinary excretion of urinary calcium (togheter with sodium, magnesium, citrate, sulfate, phosphate, oxalate, and urate), but they had also increased urinary volumes. In extremely obese women with an android phenotype, urinary excretion of calcium is elevated with an increase of bone remodelling markers.