It’s estimated that many people over 60 have only 40 percent of kidney function left. Chronic kidney disease, as it’s known, occurs gradually over the course of years. Risk factors include high blood pressure, which has devastating effects on the filtering units of the kidneys; diabetes; obesity; elevated blood fats, such as cholesterol and triglycerides; and smoking. The harm produced by those factors is related to damage of blood vessels in the kidneys or direct damage to the kidneys themselves. Much of it occurs due to a low-grade inflammation localized to the kidneys. Since omega-3 fatty acids, as found in fish oil, offer potent anti-inflammatory effects, it stands to reason that fish oil should also protect the kidneys, and that’s precisely what a recent study found.1
The researchers examined the eating habits of 2,600 people over 50. The primary results were that fish oil intake is inversely associated with the prevalence of chronic kidney disease. Just eating a lot of fish lowered the rate of chronic kidney disease by 32 percent. Conversely, taking alpha-linoleic acid, an omega-3 fatty acid precursor found in various vegetable sources, including flaxseed oil, increased the likelihood of getting chronic kidney disease by 73 percent. Although the protective effect mechanism of fish oil isn’t precisely established, several theories suggest how it occurs.
The main theory is that fish oil products protect by lowering inflammation in the kidneys. It does that by lowering the production of various inflammatory mediators, such as cytokines, and even nitric oxide, which in excess can damage the kidneys. Fish oil also lowers blood pressure, which is the major cause of kidney destruction. By helping to control elevated blood lipids, fish oil offers still another layer of protection for the kidneys. Some studies suggest that it lowers excessive protein excretion through the kidneys, which is a known harbinger of future kidney problems.
As to why alpha-linoleic acid didn’t offer any such protection, the authors note that ALA converts poorly into the more active omega-3 fatty acids, namely EPA and DHA, in the body. Even worse, consuming large amounts of alpha-linoleic acid may interfere with the metabolism of DHA though a negative-feedback mechanism, which would lower tissue concentrations of DHA. In addition, ALA doesn’t affect the inflammatory mediators as do the preformed omega-3 fats found in fish and fish oil. The study also found that omega-6 fatty acids, as contained in vegetable oils and other sources, have a negative effect on long-term kidney function, since they convert into pro-inflammatory mediators that can damage the kidneys. The good news is that omega-3 fish oil can block the damaging effect of excess omega-6 fats.
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1 Gopinath, B., et al. (2011). Consumption of long-chain N-3 PUFA, a-linoleic acid and fish is associated with the prevalence of chronic kidney disease. Br J Nutr. 105:1361-1368.