Among adults with type 2 diabetes, supplementation with vitamin D3 or omega-3 fatty acids resulted in no significant changes in serum creatinine and cystatin C (eGFR) from baseline to year 5 compared with a placebo, according to a study published in JAMA. The findings of the study do not support the use of vitamin D or omega-3 fatty acid supplementation for preserving kidney function in patients with type 2 diabetes, the study authors wrote.

Among patients with type 2 diabetes, chronic kidney disease (CKD) is common and associated with poor health outcomes. The prevalence of CKD is defined as persistently reduced glomerular filtration rate (GFR) or elevated urinary albumin excretion. This rate is more than 25% in patients with CKD.

The 2x2 factorial randomized clinical trial included 1312 participants with type 2 diabetes recruited between November 2011 and March 2014 from all 50 US states as an ancillary study to the Vitamin D and Omega-3 Trial (VITAL), coordinated by the Brigham and Women’s Hospital Department of Preventative Medicine in Boston, MA.

The study included 370 participants randomized to receive vitamin D3 (2000 IU/d) and omega-3 fatty acids (eicosapentaenoic acid and docosahexaenoic acid; 1 g/d), 333 participants who received vitamin D3 and placebo, 289 who received placebo and omega-3 fatty acids, and 350 participants who received 2 placebos for 5 years.

This study assessed change in eGFR over 5 years as the primary outcome because this is a clinically relevant outcome with which treatment effects could be assessed. An increase in eGFR is often associated with increased risk of end-stage kidney disease, cardiovascular events, and death.

At least 1 follow-up blood sample was provided by 1090 (83%) of the 1312 participants who were randomized, including 934 (71% of participants) 5 years after randomization. Additionally, urine samples were provided by 1091 participants (83%), including 945 (72% of randomized participants; 77% of those alive) 5 years after randomization.

At baseline, participants enrolled in this study had an average age of 67.6 years and a median duration of diagnosed diabetes of 6 to 10 years.

Mean baseline eGFR was 85.8 mL/min/1.73 m2 and eGFR was less than 60 mL/min/1.73 m2 for 165 participants. Mean change in eGFR from baseline to year 5 was −12.7 mL/min/1.73 m2 in the full analytic population and −12.4 mL/min/1.73 m2 among 932 participants with eGFR data at both baseline and year 5. Additionally, mean change in eGFR was −12.2 mL/min/1.73 m2 with omega-3 fatty acids vs −13.1 mL/min/1.73 m2 with placebo.

Therefore, at year 5, there was no significant difference in eGFR change according to treatment and there was no significant interaction between treatment assignments.

Adverse events were similar between both vitamin D and omega-3 fatty acid supplementation with respective placebos. Kidney stones occurred in 58 participants, of whom 32 received vitamin D3 and 26 received placebo, and gastrointestinal bleeding occurred among 45 participants, of whom 28 received omega-3 fatty acids and 17 received a placebo.

Neither vitamin D nor omega-3 fatty acid supplementation significantly slowed eGFR decline over 5 years among adults with type 2 diabetes. Secondary outcomes, including large changes in eGFR and changes in urine albumin excretion also showed no statistically significant differences between groups.

According to the study authors, altogether, these results suggest that neither vitamin D nor omega-3 fatty acids have kidney benefits among the broad population of patients with diagnosed type 2 diabetes.

Reference
  1. Boer I, Zelnick L, Ruzinski J, et al. Effect of Vitamin D and Omega-3 Fatty Acid Supplementation on Kidney Function in Patients with Type 2 Diabetes. JAMA. Published November 8, 2019. doi: https://doi.org/10.1001/jama.2019.17380 . Accessed November 12, 2019.