Chronic kidney disease is common, often progressive, and difficult to treat or prevent. Effective interventions would therefore be more than welcome. This paper explored the relation of habitual fish oil use with the risk of chronic kidney diseases (CKD).

A total of 408,023 participants (54.2% female) without prior CKD and with completed information regarding their consumption of major food groups and fish oil in the UK Biobank were enrolled. Fish oil use and dietary intakes were assessed by touch screen questionnaire and food frequency questionnaire, respectively. Incident CKD was recorded from hospital inpatient records.

At baseline, 128,843 (31.6%) participants reported taking fish oil supplements. During a median follow-up period of 12.0 years, a total of 10,782 (2.6%) participants developed CKD. With adjustments for important confounders, habitual fish oil use was associated with a significantly lower hazard of incident CKD (hazard ratio [HR], 0.90; 95% confidence interval [CI], 0.87-0.95), compared with non-use. Consistently, participants reporting ≥2 servings/week of oily fish (HR, 0.86; 95% CI, 0.79-0.94) and nonoily fish (HR, 0.86; 95% CI, 0.77-0.97) consumption had a lower hazard of incident CKD compared to those reporting no consumption ever. Additionally, among the 97,914 participants with data on plasma fatty acid, there were significant inverse relationships of plasma omega-3 polyunsaturated fatty acid (PUFA) (per SD increment, HR, 0.89, 95% CI, 0.84-0.94) and eicosatetraenoic acid (per SD increment, HR, 0.91, 95% CI, 0.87-0.96) with incident CKD.

The authors concluded that habitual fish oil use was associated with a lower hazard of CKD, which was further confirmed by the consistent inverse relations between fish consumption and circulating omega-3 PUFA concentration with incident CKD.

I like this paper! It shows in an exemplary fashion how to interpret an association between two variables: fish oil consumption does not necessarily CAUSE the lower risk, it is merely associated with it and there might be a number of non-causal explanations for the link. Whether there is a true cause-effect relationship needs to be investigated in further, differently designed studies. The present paper does not overstate its conclusions but it is nevertheless important, as it hopefully will prompt others to clarify the crucial issue of causality.

Wouldn’t it be nice, if researchers of so-called alternative medicine (SCAM) finally learned this simple lesson?

5 Responses to Habitual fish oil consumption and chronic kidney disease: there is a link, but is it causal?

  • Wouldn’t it be nice, if researchers of so-called alternative medicine (SCAM) finally learned this simple lesson? [of not assuming causality willy-nilly]

    Pardon my cynicism, but I think the alternative world has a LOT of important things to learn first, before addressing their tendency to commit the Post hoc fallacy:
    – learn to actually listen when real scientists tell them why they’re wrong, instead of rejecting criticism out of hand,
    – learn to question the assumptions and other knowledge that underpin their current beliefs,
    – learn that the scientific method is the best way to establish objective knowledge, also in their area of interest,
    – learn how to do high-quality science, avoiding the many biases, fallacies and other pitfalls that lead to false outcomes.
    And there are no doubt several more things that they should learn.

    Then again, false causality may indeed be the single most important fallacy that causes SCAM practitioners and proponents to start (and keep) believing in what they’re doing.

    • nothing to pardon here!
      these are nothing but valid thoughts.

      • I stopped taking omega three fish oil because I simply don’t know what is in them (like many supplements). Sure, the omega-3 is likely beneficial to good health. Too much omega-6 is the cause of inflammation in many patients, omega-3 counteracts the omega-6. That said, the fishes in the sea are increasingly testing out with more mercury. It’s a good choice to look for better sources of omega-3.
        While mercury from fish (omega-3) alone might not be the cause of CKD, it could be a contributing factor.

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