Risk factors for hypovitaminosis D in nondialyzed chronic kidney disease patients.

BACKGROUND: Hypovitaminosis D is highly prevalent among patients with chronic kidney disease and has been associated with worse outcome even in the earlier stages of the disease. OBJECTIVE: This study aimed to investigate the risk factors for hypovitaminosis D in nondialyzed patients with chronic kidney disease. DESIGN: This cross-sectional study included 120 patients with chronic kidney disease at stages 2 to 5 (62% male, age: 55.4 ± 11.3 year, estimated glomerular filtration rate: 35.1 ± 15 mL/minute, body mass index [BMI]: 27.1 ± 5.2 kg/m(2), 31% diabetics). Serum 25-hydroxivitamin D [25(OH)D] was measured by chemiluminescence. Subjective global assessment, total body fat (dual-energy X-ray absorptiometry), visceral and subcutaneous abdominal fat (computed tomography), and several laboratory parameters were assessed. RESULTS: Insufficiency of 25(OH)D (15 to 30 ng/mL) was observed in 55% and deficiency (<15 ng/mL) in 20% of the patients. Patients with diabetes, BMI ≥30 kg/m(2), and who had the blood collection during the winter or spring had lower levels of 25(OH)D. Serum 25(OH)D correlated inversely with parathyroid hormone, proteinuria, insulin resistance, leptin, and subcutaneous abdominal fat. The risk factors for hypovitaminosis D were diabetes (odds ratio: 3.8; 95% CI: 1.2 to 11.7; P = .022) and BMI ≥30 kg/m(2) (odds ratio: 4.3; 95% CI: 1.2 to 15.3; P = .018). In the logistic regression analysis adjusting for gender, skin color, and season of the year, diabetes and BMI ≥30 kg/m(2) were independently associated with hypovitaminosis D. CONCLUSIONS: Diabetes and obesity were the risk factors for hypovitaminosis D in nondialyzed patients with chronic kidney disease. Effective interventional protocols of vitamin D supplementation taking into account these risk factors are warranted for this population.

Vitamin D biology: from the discovery to its significance in chronic kidney disease.

Vitamin D was discovered and had its chemical structure described in the early years of the last century. Although classified as a nutrient because it was found in small quantities in butter, it soon became clear that exposure of skin to sunlight, supplies most of the vitamin D necessary for good health in human beings. Vitamin D (D3 or cholecalciferol) synthesis in the skin is extremely rapid and remarkably robust despite the complexity of the mechanisms involved. However, a number of factors related to latitude location, season, and skin characteristics can interfere with the photoproduction of vitamin D. The 2 forms of vitamin D (D3 or D2-ergocalciferol) are biologically inactive and require activation in the liver and kidney. The product of the first hydroxylation of vitamin D in the liver, 25-hydroxyvitamin D (25(OH)D), is the marker of vitamin D status. Hypovitaminosis D (serum 25(OH)D, <30 ng/mL) is highly prevalent in the general population, and patients with chronic kidney disease seem to be at higher risk for the development of hypovitaminosis D. It is believed that, besides the traditional factors, protein losses, gastrointestinal malabsorption, and defective skin synthesis of vitamin D might contribute to the elevated number of patients with suboptimal level of vitamin D status.

Hypovitaminosis D in chronic kidney disease patients: prevalence and treatment.

In the past decade, there has been accumulating evidence indicating that vitamin D may provide great health benefits. Indeed, it has been shown that vitamin D deficiency not only causes bone and mineral disturbances but also may increase the risk of many common chronic diseases. Since very few foods contain vitamin D, humans depend on sun exposure to satisfy their requirements for vitamin D. However, factors related to the location, climate, aging, skin pigmentation, and use of barriers to protect from the sun light contribute to limit the synthesis of vitamin D in the skin. Vitamin D deficiency is highly prevalent in the general population and even more common in patients with chronic kidney disease (CKD). Certain conditions associated with CKD such as protein losses and the decreased food intake can predispose these patients to hypovitaminosis D. The interest in the nutritional status of vitamin D of CKD patients has been renewed after the recognition that low circulating levels of 25 hydroxyvitamin D, and not only of the vitamin D active form (1,25 dihydroxyvitamin D), can contribute to the development of secondary hyperparathyroidism. Therefore, vitamin D supplementation with either ergocalciferol or cholicalciferol has been recommended to restore and maintain adequate vitamin D status in CKD.