Calcium and vitamin D supplementation may cause hypercalciuria and hypercalcemia in some postmenopausal women, according to a randomized, double-blind, placebo-controlled study. Clinicians should measure blood and urine calcium levels at baseline and every 3 months in women who take the supplements, the researchers say.
John Christopher Gallagher, MD, from the Bone Metabolism Unit, Creighton University, Omaha, Nebraska, and colleagues present the results of their prospective study in an article published online June 16 in Menopause.
After women turn 40 years old, they lose 0.5% to 1% of bone per year, according to the National Institutes of Health. Calcium and vitamin D supplements are given to many postmenopausal women for the prevention of osteoporosis, the authors write. The recommended dietary allowance for vitamin D3 is 600 to 800 IU/day, and the recommended dietary allowance for calcium is 1200 mg/day.
Previous research has reported an increased risk for nephrolithiasis in women who take calcium and vitamin D supplements compared with placebo.
The researchers included 163 white women aged 57 to 90 years in the study. All women were deficient in vitamin D at baseline, with serum 25-hydroxy vitamin D levels lower than 20 ng/mL (50 nmol/L).
The researchers randomly assigned women to receive vitamin D3400, 800, 1600, 2400, 3200, 4000, or 4800 IU/day or placebo. They analyzed the women’s dietary calcium levels from 7-day food diaries and gave them daily calcium citrate supplements to maintain total calcium intake between 1200 and 1400 mg/day.
The researchers collected serum and 24-hour urine calcium every 3 months during supplementation, and they considered any test result above the upper reference range to be an episode of hypercalcemia or hypercalciuria.
A total of 147 women completed the 1-year study protocol. Of those participants, 8.8% experienced hypercalcemia (910.2 mg/dL [2.55 mmol/L]) and 30.6% experienced hypercalciuria (9300 mg/d [7.5 mmol]). Hypercalciuria episodes were transient in half the group and recurred in the other half. The researchers found no relationship between hypercalcemia or hypercalciuria and vitamin D dose, and hypercalciuria was equally frequent in the placebo group.
“No relationship was found between episodes of hypercalcemia or hypercalciuria and vitamin D3 dose or serum 25(OH)D level, but 24-hour urine calcium was weakly related to the 12-month serum 25(OH)D level,” the authors write.
For women whose baseline 24-hour urine calcium level was above 132 mg, their risk of developing hypercalciuria was 15 times higher than that of women with lower levels. That risk was 20 times higher for women whose baseline levels were above 180 mg. Their risk reduced by 10% with every 1-year increase in age.