ENCINITAS, Calif. – A multi-year study of people taking Vitamin D supplements with 25-hydroxyvitamin D [25(OH)D] serum levels in the range of 20 to 100 ng/ml did not show an increased risk of kidney stones.

The study was sponsored by GrassrootsHealth (GRH), a nonprofit public health research organization, and was led by Dr. Cedric Garland, professor of family and preventive medicine at the University of California, San Diego. The research team used data collected from 2,012 participants enrolled in GRH’s D*action study. Participants were followed for an average of 19 months; all ages and both genders were included. The average 25(OH)D level was 45 ng/ml, which is higher than most other cohorts.

Evidence shows that 25(OH)D serum levels between 40-60 ng/ml provide a substantial reduction in risk of many diseases including certain cancers and diabetes. Vitamin D supplementation is often needed to achieve these levels but there is a concern about kidney stone risk with supplementation.

“Many physicians have been afraid to recommend doses of vitamin D that would produce the serum levels of 25(OH)D found in this study, which correspond to intake of approximately 4000 IU/day of vitamin D3 in adults. The findings of this study should free them from any substantial concern about raising the risk of kidney stones due to serum 25(OH)D and vitamin D intake in this range,” said Garland. “And we know of no other risks at these levels for almost every person age 9 years or older.”

Thirteen individuals reported having kidney stones during the study time; occurrences were confirmed by medical records or interview. The study found no statistically significant association between 25(OH)D serum levels and kidney stone risk. In fact, the researchers found a non-significant trend towards lower incidence of kidney stones for those with higher 25(OH)D serum levels.

Older age, male gender and higher body mass index (BMI) were risk factors for kidney stones. BMI was the only significant covariate where individuals with a BMI of 30 or greater had a 3-fold higher risk of developing kidney stones.

Study results appeared this week in the American Journal of Public Health. The paper is available as an open access publication.

Dr. Garland was joined by Stacie Nguyen, Leo Baggerly and Christine French of GrassrootsHealth; Robert P. Heaney of GrassrootsHealth and the Department of Medicine at Creighton University in Omaha, Nebraska; and Edward D. Gorham of UC San Diego Department of Family and Preventive Medicine.

The study was supported by the participants of the D*action study at GrassrootsHealth.

View the manuscript here