Here are some studies about vitamin D and chronic kidney disease:
Prevalence of 25(OH) Vitamin D Insufficiency and Deficiency in Pediatric Patients on Chronic Dialysis (2013)
Conclusion: The vitamin D blood levels of 59 South Korean pediatric kidney disease patients were measured. 83% had levels below 30 ng/ml with the average level being only 19 ng/ml.
Conclusion: The vitamin D levels of 125 Brazilian predialytic chronic kidney disease patients were measured. Despite living in a tropical region with lots of sunshine, 72% shockingly had levels below 30 ng/ml, with 21% in the clinical deficiency range. Most vitamin D researchers now agree that 50 ng/ml should be considered the minimum healthy vitamin D level, so probably more than 72% had a low level. This article also cites another study, which found 77% of Sao Paulo, Brazil’s general population had levels below 30 ng/ml.
Conclusion: This study of 80 child chronic kidney disease patients in Saudi Arabia found that the children had lower vitamin D levels compared to healthy controls, with 88% having levels below 30 ng/ml. If the more modern vitamin D sufficiency standard of 50 ng/ml were used the results of this study would be even more dismal.
Conclusion: This study of 125 Brazilian chronic kidney disease patients found that 72% of them had low vitamin D levels. This study used a slightly outdated vitamin D sufficiency standard, however, so the insufficiency rate was probably higher. Important to note is that these subjects were living in tropical, sunny Brazil, yet were still failing to achieve optimal vitamin D levels.
Prevalence of Calcidiol Deficiency in CKD: A Cross-Sectional Study Across Latitudes in the United States. (2005)
Conclusion: The vitamin D levels of 201 chronic kidney disease patients were evaluated. 71% of moderate CKD patients had insufficient vitamin D levels and 83% of severe CKD patients had insufficient levels.
Vitamin D Insufficiency and Deficiency in Chronic Kidney Disease – A Single Center Observational Study (2004)
Conclusion: This study of 43 chronic kidney disease patients found that 86% had low vitamin D levels under 30 ng/ml. Again, 30 ng/ml is becoming an outdated sufficiency standard with many leading vitamin D researchers agreeing that 50 ng/ml is actually the minimum optimal level. If that standard were applied in this study the results would have been worse.