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?