Vitamin D Repletion Does Not Alter Urinary Calcium Excretion In Healthy Postmenopausal Women

Main Category: Urology / Nephrology
Also Included In: Women's Health / Gynecology
Article Date: 06 Aug 2009 - 1:00 PDT

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UroToday.com - Vitamin D needs, especially in the northern latitudes where direct sunlight is unavailable for much of the year, are currently under scrutiny by members of both the scientific and medical communities. Vitamin D primarily plays a role in regulating calcium absorption in the gastrointestinal tract. However, epidemiologic and laboratory studies support the notion that vitamin D might play a role in chemoprevention - particularly of cancers of the colon, breast, ovarian, and prostate (Garland et al., Am J Public Health 2006;96:252-61) - immune modulation and prevention of certain autoimmune disorders (Cantorna et al., Exp Biol Med 2004;229:1136-1142), promoting bone integrity and preserving muscle mass (Montero-Odasso et al., Mol Aspects Med 2005;26:203-19), cardiovascular disease prevention (Wang et al., Circulation 2008;117:503-11), and prevention of all-cause mortality (Melamed et al., Arch Intern Med 2008;168:1629-37).

Current vitamin D recommendations too low? The current recommended intake values for vitamin D were established in 1997 by the Institute of Medicine of The National Academies, which is responsible for publishing The Dietary Reference Intakes (DRIs), a set of nutrient recommendations for >40 essential macronutrients, vitamins, and minerals based on age, gender, and lifestage.

In light of mounting evidence of both the frequency of low vitamin D status and newly-appreciated roles for vitamin D, and following pleas from such organizations as the Canadian Pediatric Society, the American Medical Association, and the American Academy of Pediatrics, a review of vitamin D needs was initiated earlier this year. The anticipated outcome of this review is 2010, at which time new recommendations for vitamin D are expected.

To dose or not to dose: that is the question. As a growing number of individuals are reportedly supplementing with vitamin D in an effort to protect against various sequelae related to vitamin D insufficiency, it seems imperative to determine whether this practice should be recommended in calcium stone formers, especially as they may suffer from some of the same comorbidities purported to be managed with vitamin D intakes above the current recommendations.

For many years, calcium stone formers have been instructed to avoid vitamin D supplementation for fear that it may contribute to or exacerbate hypercalciuria. However, data supporting this recommendation are scarce. We ascertained the safety of vitamin D repletion in vitamin D insufficient post-menopausal women with respect to 24-h urinary calcium excretion. We undertook this evaluation as a first step towards the planning and implementation of a vitamin D repletion/supplementation study in stone formers.

Vitamin D repletion did not alter urinary calcium excretion. Calcium absorption increased nominally (3%, p = 0.04) in post-menopausal women after vitamin D repletion with 50,000 IU ergocalciferol daily for 15 days, without a change in urinary calcium excretion. Such data suggest that vitamin D repletion might also be safe in calcium stone formers with and without hypercalciuria.

While post-menopausal women carry a higher risk for urolithiasis than younger women and are thus a good model for urolithiasis research, the safety of higher vitamin D intakes in stone formers should be rigorously assessed. This information is crucial if we are to make evidence-based recommendations about vitamin D to calcium stone formers, especially if vitamin D recommendations are increased, as is expected, within the next year.

Written by Kristina L. Penniston, PhD, and Karen E. Hansen, MD as part of Beyond the Abstract on UroToday.com.

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