Calcium and vitamin D supplements are associated with high calcium levels in the blood and urine, which could increase the risk of kidney stones, a new study finds. The results will be presented Tuesday at The Endocrine Society's 94th Annual Meeting in Houston.
"The use of calcium and vitamin D supplementation may not be as benign as previously thought," said principal investigator J. Christopher Gallagher, M.D., professor and director of the Bone Metabolism Unit at Creighton University Medical Center in Omaha, NE. "Pending further information, people should not exceed the guidelines suggested by the Institute of Medicine, which are 800 international units of vitamin D, and 800-1,200 milligrams per day of calcium."
Taking vitamin supplements has become a widespread practice throughout many parts of the world. In the United States alone, it is estimated that nearly two-thirds of women take vitamin supplements, with calcium and vitamin D among the most commonly used. Despite their popularity, the precise health effects of long-term calcium and vitamin D supplementation remain unclear.
Previous research has indicated that high levels of calcium in the urine, or hypercalciuria, may increase the risk of kidney stones. Elevated calcium in the blood, or hypercalcemia, is associated with many complications, including bone and kidney problems.
Gallagher and study lead author Vinod Yalamanchili, M.D., research fellow in Creighton University's Bone Metabolism Unit, studied 163 healthy, postmenopausal women between the ages of 57 and 85 years. All participants were randomly assigned to receive a vitamin D supplement of 400, 800, 1600, 2400, 3200, 4000, or 4800 international units a day, or placebo. Then, their calcium intake was increased from an initial intake of 691 to 1,200-1,400 milligrams per day. Investigators measured blood and urinary calcium levels at the beginning of the study, and then every three months for one year.