People who eat more fish tend to show slower cognitive decline in observational studies. That’s encouraging, but it doesn’t prove that fish oil capsules protect memory.

When researchers tested omega-3 supplements in randomised trials, the results were largely disappointing. In cognitively healthy older adults, large trials and reviews have generally found little or no benefit for memory or thinking skills. There are hints of benefit in people with low dietary omega-3 intake or very mild memory complaints, but that evidence is early and inconsistent.

DHA is a major structural fat in the brain, so omega-3s clearly matter biologically. The question is whether adding more through a pill helps if you’re already getting enough. Eating fish is also different from taking an isolated oil, since fish provides protein, iodine, selenium and vitamin D.

Australia’s NHMRC suggests dietary targets of about 430 mg (women) and 610 mg (men) of combined DHA, EPA and DPA daily. Two to three serves of oily fish like salmon, sardines or mackerel each week gets most people there.

Take care: high-dose fish oil can increase bleeding risk and may interact with blood thinners. It has also been linked to a higher risk of atrial fibrillation at high doses. Talk to your doctor first.

Bottom line: Eat the fish. If you don’t, a supplement is reasonable, but don’t expect it to sharpen your memory.