Original Investigation
Pathogenesis and Treatment of Kidney Disease
25-Hydroxyvitamin D Levels and Albuminuria in the Third National Health and Nutrition Examination Survey (NHANES III)

https://doi.org/10.1053/j.ajkd.2007.04.015Get rights and content

Background

Albuminuria is a risk factor for chronic kidney disease progression, end-stage renal disease, cardiovascular events, and mortality. Animal studies suggested that vitamin D insufficiency may contribute to the pathogenesis of albuminuria.

Study Design

Cross-sectional study.

Setting & Participants

15,068 adults participating in the Third National Health and Nutrition Examination Survey.

Predictor

Serum 25-hydroxyvitamin D concentration, examined in quartiles.

Outcomes & Measurements

Albuminuria, defined using established sex-specific cutoff values for urine albumin-creatinine ratio (25 to 2,999 mg/g for women, 17 to 2,999 mg/g for men).

Results

A stepwise increase in the prevalence of albuminuria was observed with decreasing quartiles of vitamin D concentration: 8.9%, 11.5%, 13.7%, and 15.8% (P < 0.001). Adjusting for age, sex, race/ethnicity, region and season of measurement, smoking status, body mass index, and estimated glomerular filtration rate, relative risks for albuminuria by decreasing quartile of vitamin D concentration were 1.00 (reference group), 1.14 (95% confidence interval, 0.95 to 1.37), 1.22 (95% confidence interval, 1.03 to 1.45), and 1.37 (95% confidence interval, 1.10 to 1.71; P = 0.006). Additionally adjusting for blood pressure and diabetes mellitus, these risks were somewhat attenuated and retained statistical significance.

Limitations

The cross-sectional design of this study does not allow demonstration of temporal or causal relationships between vitamin D and albuminuria.

Conclusions

Additional studies are needed to clarify the relationship of vitamin D with albuminuria and determine whether vitamin D therapy prevents or improves markers of kidney and cardiovascular disease.

Section snippets

Study Population

NHANES III was a population-based survey conducted from 1988 to 1994.21 It was designed to provide national estimates of health and nutritional status for the civilian noninstitutionalized population of the United States. Young children, older persons, black persons, and Mexican Americans were oversampled as part of a complex multistage sample design. A total of 16,575 participants aged 20 years or older were included in a mobile examination center evaluation, of whom 15,395 (93%) underwent

Results

Serum 25-hydroxyvitamin D levels were distributed in a log-normal fashion (Fig 1). Proportions of subjects with vitamin D levels less than 12, 20, and 32 ng/mL (<30, 50, and 80 nmol/L; proposed definitions of vitamin D deficiency27) were 3.7%, 22.2%, and 62.7%, respectively. Lower vitamin D levels were associated with older age, female sex, history of diabetes, hypertension, greater BMI, and lower estimated GFR (Table 1). Mean vitamin D levels varied by race/ethnicity, with the highest levels

Discussion

Low 25-hydroxyvitamin D levels were associated with an increased prevalence of albuminuria in a large representative sample of the US population. Prevalence of albuminuria increased in a progressive fashion with decreasing vitamin D levels, and the association of low vitamin D level with albuminuria was independent of age, sex, race/ethnicity, smoking status, BMI, and kidney function. Adjustment for hypertension and diabetes resulted in some attenuation of this association, suggesting that

Acknowledgements

Support: This publication was made possible by grant 5 K12 RR023265-03 from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH). Its contents are solely the responsibility of the authors and do not necessarily represent the official view of NCRR or NIH.

Financial Disclosure: None.

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