The association of vitamin D deficiency and insufficiency with diabetic nephropathy: implications for health disparities.

OBJECTIVE: To evaluate the association between vitamin D deficiency and insufficiency with diabetic nephropathy across racial/ethnic groups.

METHODS: Cross-sectional analysis of the 2001 to 2006 National Health and Nutrition Examination Survey. A nationally representative sample of 1216 adults (> or =20 years old) with diagnosed diabetes provides population estimates for >12.6 million individuals. Nephropathy was defined as urinary albumin-to-creatinine ratio > or =30 mg/g in a random spot urine sample. Serum 25-hydroxycalciferol vitamin D levels were characterized as <20 ng/mL vitamin D deficiency, 20 to 29 ng/mL vitamin D insufficiency, and > or =30 ng/mL normal vitamin D.

RESULTS: Overall, 30.7% of adults with diabetes have nephropathy, 48.9% have vitamin D deficiency and 36.6% have vitamin D insufficiency. Minorities are more likely to have nephropathy (non-Hispanic whites, 27.8%; non-Hispanic blacks, 36.2%; Hispanics 38.5%; P = .02) and vitamin D deficiency (non-Hispanic whites, 39.5%; non-Hispanic blacks, 80.4%; Hispanic, 59.0%; P < .01). Higher proportions of individuals with nephropathy have vitamin D deficiency than individuals without nephropathy (53.2% vs 47.0%; P = .03). Logistic regressions demonstrate vitamin D deficiency and insufficiency are associated with the presence of nephropathy after adjustment for race/ethnicity, age, sex, hypertension, high cholesterol, smoking status, and use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers (odds ratio, 1.85; 95% CI, 1.06-3.23 for vitamin D deficiency; and odds ratio, 1.79; 95% CI, 1.12-2.85 for vitamin D insufficiency).

CONCLUSIONS: There is a high prevalence of vitamin D deficiency and insufficiency in individuals with diabetes; minorities have the highest prevalences. Thus, evaluating vitamin D levels in people with diabetes may be warranted. There is an independent association between vitamin D deficiency and vitamin D insufficiency with the presence of nephropathy, even after adjustment for race/ethnicity and other variables. Further studies of this relationship may lead to new interventions that decrease health disparities in the progression of diabetic nephropathy.