Omega-3 moved lipids and blood pressure, not kidney function

Diabetic kidney disease is a major microvascular complication of diabetes and a growing contributor to global disease burden. Polyunsaturated fatty acids have long been proposed to influence its development through anti-inflammatory and antioxidant mechanisms, which is why fish-oil supplements are so often discussed in this setting. The problem is that the existing evidence has been inconsistent and the mechanisms unclear, leaving open whether omega-3 exposure is genuinely protective or merely tracks with healthier diets and lifestyles. This study set out to attack the question from several angles at once.

The authors combined three approaches. First, a two-sample Mendelian randomisation analysis used genome-wide association data to test whether genetically predicted plasma omega-3 and omega-6 levels relate to diabetic kidney disease risk, an approach designed to reduce confounding. Second, a two-step protein-mediated Mendelian randomisation framework with plasma proteomic panels and Reactome pathway enrichment looked for mediating proteins and biological pathways. Third, they meta-analysed 12 randomised controlled trials including 474 participants to assess what omega-3 supplementation actually does to clinical markers in people with diabetic kidney disease.

Genetically predicted higher plasma omega-3 was associated with reduced disease risk (OR 0.869, 95% CI 0.772-0.978, p = 0.020), whereas omega-6 was not (OR 0.895, 95% CI 0.731-1.096, p = 0.283). Fourteen plasma proteins showed nominally significant partial mediation with consistent direction and mediation proportions from 2.10% to 29.80%, including neuronal pentraxin-2, haemoglobin subunit theta-1 and periostin; enriched pathways involved Notch signalling, apoptosis regulation and chronic inflammation. In the trials, omega-3 reduced triglycerides (-0.27 mmol/L), systolic blood pressure (-4.50 mmHg) and kidney injury molecule-1 (-1.74 pg/mL), and raised HDL cholesterol (+0.14 mmol/L), but albumin-to-creatinine ratio and estimated glomerular filtration rate did not significantly improve.

The genetic arm strengthens the case that omega-3 status, rather than omega-6, is the fraction plausibly linked to kidney risk, which complicates the habit of treating all polyunsaturated fats as interchangeable. The trial arm confirms omega-3's familiar effects on lipids and blood pressure but stops short of demonstrating benefit on the outcomes clinicians care most about, namely albuminuria and filtration rate. That gap is the central open question: whether an early injury marker such as kidney injury molecule-1 translates into preserved kidney function over years. The mediation signals are hypothesis-generating rather than established mechanism.

This is a reason to think omega-3 intake sits on the favourable side of cardiometabolic risk, particularly for triglycerides, HDL cholesterol and systolic blood pressure, and that a genetic signal points in the same direction for kidney risk. It is not evidence that supplements repair kidney function, since the two standard measures of kidney health did not move. The trial evidence is small and drawn from people who already have diabetic kidney disease, so it says little about prevention in healthy adults. Anyone with diabetes or kidney disease is in territory where decisions belong with their clinical team.