Calcium supplementation and abnormal calcium in blood and urine
Calcium supplementation is often recommended without careful determination of individual need and tolerance. Conflicting studies have raised the suspicion of an increase in cardiovascular risk associated with calcium (which may occur when the anti-inflammatory effects of magnesium are opposed). A study just published in the journal Menopause offers evidence that for a significant percentage of women modest calcium supplementation produces abnormally high levels in blood (hypercalcemia) and urine (hypercalciuria).
"This study aims to prospectively assess the incidence of hypercalciuria and hypercalcemia with different doses of vitamin D and with a calcium intake of approximately 1,200 mg/day."
The authors conducted a 1-year randomized placebo-controlled study in which 163 white women aged 57 to 90 years were given calcium citrate tablets (200 mg) to achieve a total calcium intake (diet plus supplements) of approximately 1,200 mg/day in all groups, and vitamin D (400-4,800 IU/d). Incidentally...
"All women had vitamin D insufficiency at baseline, with serum 25-hydroxyvitaminD levels lower than 20 ng/mL (50 nmol/L)."
(This is egregiously low for case management of autoimmunity.) They measured serum and 24-hour urine calcium every 3 months while on supplementation marking any test result above the upper reference ranges as episodes of hypercalcemia or hypercalciuria. Mixed-effects models and multivariate logistic regression were used in the analysis. Their data show that even modest supplementation may be too much for some women:
"Hypercalcemia (>10.2 mg/dL [2.55 mmol/L]) occurred in 8.8% of white women. Hypercalciuria (>300 mg/d [7.5 mmol]) occurred in 30.6% of white women. Episodes of hypercalciuria were transient in half of the group and recurrent in the other half. No relationship between hypercalcemia or hypercalciuria and vitamin D dose was found, and hypercalciuria was equally common in the placebo group."
So the small doses of vitamin D were apparently not responsible for the excess calcium in urine or blood. Medscape Family Medicine quotes the authors:
"Even a modest calcium supplementation of 500 mg/day may be too high for some women,” the authors note in a news release. They recommend measuring blood and urine calcium levels before beginning calcium and vitamin D supplementation and repeating the measurements within 3 months."
Medscape also quotes Margery Gass, MD, execustive director of the North American Menopause Society:
“I would recommend that women determine how much calcium they typically get through their food sources before taking a hefty calcium supplement. They may not need as much as they think.”
Clinical note: It is prudent to not give any supplement without objective indications of need and tolerance. Moreover, osteoporosis is not a calcium deficiency disorder but rather a decline in the protein matrix of bone to which minerals attach.Practitioners should bear in mind the authors' conclusion:
"Hypercalciuria and hypercalcemia commonly occur with vitamin D and calcium supplements...These findings may have relevance to the reported increase in kidney stones in the Women's Health Initiative trial. Because calcium 1,200 mg and vitamin D 800 IU/day are widely recommended in postmenopausal women, systematic evaluation of the safety of supplements is warranted in clinical management and in future studies."