Vitamin D and Omega-3 Fatty Acid has no Effect on Kidney Function

Ian H. de Boer, MD, MS

Vitamin D and omega-3 fatty acid interventions may not be a cure for improving kidney function in patients with type 2 diabetes.

A team of investigators, led by Ian H. de Boer, MD, MS, Division of Nephrology, Department of Medicine, University of Washington, examined whether vitamin D or omega-3 fatty acid supplements help prevent the development or progression of kidney disease in adults with type 2 diabetes.

In the 2 x 2 factorial randomized clinical trial, 1312 patients with type 2 diabetes were examined, with no significant differences observed in the changed in estimated glomerular filtration rate (eGFR) at 5 years with vitamin D₃ supplementation compared with a placebo (−12.3 vs −13.1 mL/min/1.73 m²) or with omega-3 fatty acid supplementation vs placebo (−12.2 vs −13.1 mL/min/1.73 m²).

The mean age of the study was 67.6 years old, with 46% of the participants being women and 31% being a racial or ethnic minority.

The baseline mean was 85.8 (SD, 22.1) mL/min/1.73 m² and the mean change in eGFR from baseline to year 5 was −12.3 (95% CI, −13.4-−11.2) mL/min/1.73 m² with vitamin D₃ vs −13.1 (95% CI, −14.2-−11.9) mL/min/1.73 m² with placebo (difference, .9 [95% CI, −.7-2.5] mL/min/1.73 m²).

The mean change in eGFR was −12.2 (95% CI, −13.3-−11.1) mL/min/1.73 m² with omega-3 fatty acids vs −13.1 (95% CI, −14.2-−12.0) mL/min/1.73 m² with placebo (difference, .9 [95% CI, −0.7-2.6] mL/min/1.73 m²).

The investigators did not observe a significant interaction between the 2 interventions.

They also found that 58 patients (n=32 receiving vitamin D_3­ and n=26 receiving placebo) suffered from kidney stones, while 45 participants (n=28 receiving omega-3 fatty acids and n=17 receiving placebo) suffered from gastrointestinal bleeding.

Participants in the study received either 2000 IU/d of vitamin D₃ and 1 g/d of eicosapentaenoic acid and docosahexaenoic acid, vitamin D₃ and a placebo, omega-3 fatty acids and a placebo, or 2 placebos for 5 years.

Chronic kidney disease is often a complication for patients with type 2 diabetes, which can ultimately lead to end-stage kidney disease and a high cardiovascular risk. There are currently very few treatment options available to prevent chronic kidney disease in type 2 diabetes patients.

The primary outcome was change in eGFR from serum creatinine and cystatin C from baseline to year 5.

“These findings do not support the use of vitamin D or omega-3 fatty acid supplementation for preserving kidney function in adults with type 2 diabetes,” the authors wrote.

During American Society of Nephrology (ASN) Kidney Week in Washington, D.C., investigators presented data showing the consistent renal and cardiovascular benefit in treating patients with moderate to severe renal deficiency with canagliflozin, the only diabetes medicine indicated to slow down the progression of diabetic nephropathy.

The medication also reduces the risk of hospitalization for heart failure in patients with type 2 diabetes and diabetic nephropathy.

In the CREDENCE study, the investigators found patients with various levels of kidney function or eGFR benefit with a reduced risk of renal and cardiovascular events.

In the secondary analysis, the team sough to test whether the effects of the treatment on clinically important outcomes were consistent across all eGFR screening levels.

The study included 4401 patients, 1313 (30%) of which had moderately to severely decreased kidney function (eGFR 30 to <45 mL/min/1.73 m²), while 1279 (29%) had mildly to moderately decreased kidney function (eGFR 45 to <60 mL/min/1.73 m²) and 1,809 (41 percent) had mildly decreased kidney function (eGFR 60 to <90 mL/min/1.73 m²).

Canagliflozin was particularly effective when compared to placebo in reducing the composite of cardiovascular death or hospitalization for heart failure by 31% (events occurred in 40.7 vs 59.1 participants, respectively, per 1000 patient-years; HR, .69; 95% CI, .50-.94).

The study, “Effect of Vitamin D and Omega-3 Fatty Acid Supplementation on Kidney Function in Patients With Type 2 Diabetes,” was published online in JAMA.