Omega-3 fatty acids get good reviews as potent brain food: They're talked up for improving cognitive function in everyone from newborns to senior citizens. But Alzheimer's patients don't see these benefits, according to a new study. The work follows a paper published 2 weeks ago with the same disappointing result in babies born to women taking the supplements.
That doesn’t mean omega-3s are useless: Other research has found that they may help the heart and other body systems. But when it comes to the brain, researchers concede, it looks like these fatty acids may not live up to their billing.
Both failed studies followed optimistic observational research and animal work. People who eat lots of fish are less likely to develop dementia or cognitive problems late in life. Observational studies have also found that taking omega-3s during pregnancy can reduce postpartum depression and improve neurodevelopment in children. What's more, animals with an Alzheimer's-like condition are helped by docosahexaenoic acid (DHA), one of several omega-3 fatty acids. And DHA disappears from the brains of people with Alzheimer's. All of this suggested that certain populations would benefit from upping their dose of DHA, says neurologist Joseph Quinn of Oregon Health and Science University in Portland.
But does the supplement really help? To find out, Quinn and his colleagues tested DHA's effects on Alzheimer's by recruiting 402 people with mild and moderate disease. They randomly assigned the volunteers to take DHA or a placebo. Just 295 people completed the study. Quinn thinks the slightly higher than expected dropout rate "was driven by a perception that this intervention was ineffective." Even so, the team still had enough data to conclude that DHA hadn't helped. Those taking it were no better off than those taking placebos, the team reports  today in The Journal of the American Medical Association (JAMA).
“It’s a very solid and unfortunately negative result,” says Quinn. He thinks now that the intervention came too late, and he’s not alone. “If you’ve got big holes in your brain, no amount of DHA” is going to seal them up, says Alan Dangour, a public health expert and nutritionist at the London School of Hygiene & Tropical Medicine. Both believe the study might have had a better shot at success if it had examined DHA’s ability to prevent Alzheimer’s—but that requires an enormous investment of time and money.
Still, Quinn’s study is “the biggest, best study ever done” looking at this question, says Dangour. Last year, he and his colleagues reported that in a group of 15,000 people in 10 countries, those who consumed more fish were less likely to develop dementia. “That’s been shown loads and loads of times,” he says, and “it looks like there’s some link.” But the connection may not be in the fish, he says. Instead, it could be in what the fish-eaters aren’t consuming—for example, meats with saturated fat that have been associated with dementia.
Another question for scientists is whether in healthy people more DHA really makes much difference. That’s something that Maria Makrides, a nutritionist at the University of Adelaide in Australia, is considering. She and her colleagues reported 2 weeks ago in JAMA that among 2399 pregnant women, DHA-rich fish oil capsules did not improve cognitive and language development in their children by 18 months of age. Nor did the supplements help prevent postpartum depression, something else that had been attributed to them in the past.
“Although at one level it makes a lot of sense” to give pregnant women DHA, “we actually also need to consider the physiologic adaptations that happen during pregnancy”—for example, whether pregnant women can make more DHA from precursor fatty acids than women who aren’t pregnant. There’s some evidence for that, she says.
In some narrower populations, extra DHA might make a difference, however: Last year, Makrides and her colleagues reported that premature babies benefit from getting extra DHA, probably because they are essentially missing much of the last trimester of pregnancy, when they would normally accumulate vast DHA stores. In Quinn’s study, there were hints that people who do not carry a version of a gene linked to Alzheimer’s, ApoE4, might also be helped by DHA—but although that’s something to look at in the future, right now it’s still a “soft finding,” says Quinn, of limited significance.