Low levels of vitamin D may account for nearly 60 percent of the elevated risk of end-stage renal disease (ESRD) in African Americans, according to a report in the December 2009 Journal of the American Society of Nephrology (JASN). "Our study adds to previous evidence linking vitamin D deficiency to the progression of kidney disease and the need for dialysis," comments Michal L. Melamed, MD, of Albert Einstein College of Medicine (Bronx, NY). "It also explains a fair amount of the increased risk of ESRD in African Americans." Vitamin D is obtained from sun exposure, food and food supplements.
Melamed and colleagues analyzed a nationwide sample of 13,000 Americans, including measurements of the vitamin D metabolite 25(OH)D. Medicare data were used to identify participants who eventually required dialysis therapy for ESRD. "We found that the participants with the lowest 25(OH)D levels were 2.6 times as likely to end up on dialysis compared to those with higher levels," says Melamed.
The researchers then tested whether 25(OH)D levels could contribute to the higher risk of ESRD in African Americans, compared to whites. "African Americans have lower 25(OH)D levels and a higher risk of ESRD," Melamed explains. "We found that 25(OH)D deficiency was responsible for about 58 percent of the excess risk for ESRD experienced by African Americans."
Vitamin D deficiency is a very common problem in the United States. In recent years, studies have linked low vitamin D to many different health problems, including diabetes, high blood pressure, cancers, and heart disease. The new results add to previous evidence that low 25(OH)D levels are an important risk factor for ESRD. "This is another good reason to make sure that people get enough vitamin D," Melamed adds.
Although it can't prove any cause-and-effect relationship, the study also suggests that vitamin D deficiency is a key contributor to the high risk of ESRD in African Americans. More research is needed to confirm these findings, and to determine whether treatment to raise low vitamin D levels can help to preserve kidney function. "We are currently in the process of enrolling for a clinical trial of vitamin D repletion in patients with chronic kidney disease to further test these hypotheses," says Melamed.
Dr. Melamed's research will also be presented as part of a Poster Session during ASN Renal Week on October 30, 2009. This poster presentation is entitled, "25-Hydroxyvitamin D Levels and Progressive Kidney Disease: Contribution to the Excess Risk of ESRD in Non-Hispanic Blacks" (F-PO1101).
Other authors included Paul Muntner, PhD (University of Alabama at Birmingham); Thomas Hostetter, MD (also of Albert Einstein College of Medicine); Erin Michos, MD; Brad Astor, PhD (Johns Hopkins School of Medicine); and Neil R. Powe, MD, MBA, FASN (University of California- San Francisco). Dr Hostetter has consulted for Bristol Myers Squibb, Eli Lilly, and Wyeth. None of the other co-authors reported financial disclosures.
The study entitled, “25-Hydroxyvitamin D Levels, Race, and the Progression of Kidney Disease,” will appear in an upcoming issue of JASN, and online at http://jasn.asnjournals.org/ on October 29, 2009, doi 10.1681/ASN.2009030283.
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Black individuals have lower 25-hydroxyvitamin D [25(OH)D] levels and experience a disproportionate burden of ESRD compared with white individuals. Animal studies suggest that vitamin D has renoprotective effects. We evaluated the contribution of low 25(OH)D levels on incidence of ESRD using data from the Third National Health and Nutrition Examination Survey-linked Medicare claims files (n = 13,328). We included baseline (1988 through 1994) measurements of 25(OH)D and assessed the incidence of ESRD through July 31, 2001. Overall, 34% of non-Hispanic black individuals had 25(OH)D levels <15 ng/ml compared with 5% of non-Hispanic white individuals (P < 0.001). During a median of 9.1 yr, 65 participants developed ESRD. After adjustment for demographic, socioeconomic, and clinical and laboratory factors (including diabetes, hypertension, estimated GFR, and albuminuria), participants with 25(OH)D levels <15 ng/ml had a 2.6-fold greater incidence of ESRD than those with levels > or =15 ng/ml (incidence rate ratio 2.64; 95% confidence interval [CI] 1.00 to 7.05; P = 0.05). After adjustment for clinical covariates but not 25(OH)D levels, non-Hispanic black individuals had a 2.83-fold (95% CI 1.03 to 7.77) higher risk for developing ESRD compared with non-Hispanic white individuals. Additional adjustment for 25(OH)D levels reduced the risk by 58% (incidence rate ratio 1.77; 95% CI 0.38 to 8.21). In summary, low 25(OH)D levels associate with development of ESRD even after adjustment for multiple risk factors. Low 25(OH)D levels may account for a substantial proportion of the increased risk for ESRD experienced by black individuals.
Melamed ML, Astor B, Michos ED, Hostetter TH, Powe NR, Muntner P. 25-hydroxyvitamin D levels, race, and the progression of kidney disease. J Am Soc Nephrol. 2009 Dec;20(12):2631-9. Epub 2009 Oct 29. PMID: 19875805
American Society of Nephrology (ASN) Released: 10/27/2009