Vitamin D supplements continue to be a hot topic. The risk of kidney stones from taking vitamin D supplements is not completely clear. A new study published in the American Journal of Public Health found no risk of kidney stones with higher vitamin D blood levels.
A higher risk of kidney stones was originally reported in the Women’s Health Initiative. Women who took 400 IU daily and 1000 milligrams of calcium daily were more likely to have kidney stones than those not taking regular supplements. In a recent analysis of risk and benefits, WHI researchers concluded the risk of kidney stones was small. In addition, no vitamin D blood levels were assessed.
Researchers lead by Dr. Cedric Garland at the University of California, San Diego evaluated a group of 2000 volunteers who had their vitamin D blood levels measured as part of a project sponsored by the organization GrassrootsHealth, called D*action.
The participants were sent a vitamin D test kit that uses a blood spot test analyzed by ZRT Labs for a $60.00 fee. Dr. Garland and colleagues evaluated the individuals who completed at least 2 questionnaires and provided at least 2 blood samples six months or more apart. A total of 13 individuals were identified with the diagnosis of kidney stones. Eight men and 5 women had kidney stones confirmed by medical record or interview.
The average vitamin D level of the participants was higher than general population. This reflects the study population who were interested in vitamin D and paid for the tests. The 13 who developed kidney stones had an average of 47 ng/ml and those without kidney stones, 50 mg/ml.
The study found no statistically significant association between vitamin D blood levels and kidney stone risk.
Dr. Garland stated, “Our results may lessen concerns by individuals about taking vitamin D supplements, as no link was shown between such supplementation and an increased risk for kidney stones.”
This self-selected group of individuals who were interested in tracking their vitamin D levels were likely taking doses larger than those of the general population to achieve vitamin D blood levels in the high 40-50 range. Given their higher levels, if vitamin D supplementation was a cause of kidney stones then higher risk may have been observed. However, the small number of cases of kidney stones did not provide power to prove or disprove the risk kidney stones with vitamin D supplementation.
The complete study is available as an open access publication.