These days, we've gotten used to looking for fish oil not just on pharmacy shelves and in fish like tuna, mackerel and salmon, but also as omega-3 fatty acids in fish-oil-fortified margarine, eggs, cookies, energy bars, and orange juice. We'll even pay a premium, because we were led to believe that omega-3s could ward off Alzheimer's disease, depression, and maybe stupidity. A new study today, though, indicates we may have been sold a bill of goods. Taking a fairly high dose of fish oil is no better than a placebo at stopping the progression of mild Alzheimer's disease, according to a study published in the Journal of the American Medical Association. "These are disappointing and negative results," said study author Joseph Quinn at a press conference this morning in Washington, D.C.
They are indeed, especially in the light of another disappointing study published last month in JAMA. That one found that fish oil capsules didn't prevent postpartum depression any better than vegetable oil capsules did in women who took them during pregnancy. Nor did babies born to fish-oil takers have any mental boost in terms of cognitive skills or language development. I can't help but wonder whether fish oil is ready to join the ranks of other washed-up "superstar" nutrients. Remember the wonders of oat bran? Probably not, if you're under 30.
Supplements can help if we're truly deficient in a nutrient, like vitamin C to prevent scurvy or vitamin D to prevent rickets. But too many of us have adopted a more-is-better approach thanks to studies showing that those with the "highest levels" of a certain nutrient were the healthiest. Vitamin C, vitamin E, zinc, and beta carotene all once had promising health claims affixed to them for this reason but were discredited after clinical trials found that those randomly assigned to take a particular supplement were no less likely—and sometimes were more likely—to wind up with heart disease, cancer, or a cold. Vitamin D is the current nutritional rock star. Doctors are routinely testing blood levels of vitamin D and recommending megadose supplements to prevent every health ill you can think of, from breast cancer to osteoporosis to dementia to diabetes. That's because studies suggest that those with the highest vitamin D levels have the lowest rates of these diseases.
Unlike other discredited nutrients, vitamin D still lacks studies to see who fares better, those taking the supplement or those taking a placebo. Researchers are just now starting to conduct such trials. Only after results are analyzed will we find out whether doctors have been too quick to push vitamin D supplements. Meanwhile, as JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital in Boston and lead investigator in a large clinical trial of vitamin D supplementation, told me in an interview last March, "let's not jump on the bandwagon and take megadoses before we have results from research trials."
Still, it's hard to be cautious when it comes to supplements. We rely on logic, or rather apparent common sense, to guide us: With fish oil, previous studies have shown that those who eat fish several times a week have a reduced risk of Alzheimer's. Animal studies also found that one component of fish oil, docosahexaenoic acid or DHA, stopped Alzheimer's in its tracks by reducing the amount of amyloid plaque, a hallmark sign of the disease, in the brain. But as Quinn pointed out in the press conference, this was all "circumstantial evidence." His study did everything right to find proof that fish oil supplementation worked. The researchers started with 400 folks with mild Alzheimer's who neither ate fish regularly nor took fish oil supplements and assigned them at random either to a group on two grams a day of DHA (roughly the amount in eight ounces of salmon) or to a group on a placebo. During the study, blood levels of DHA, as hoped, rose in the supplement takers and didn't change in the placebo takers. Researchers even sampled brain fluid from some of the participants, verifying that DHA was passing into the brain. The research highlights "the high-quality investigation essential for progress," writes Kristine Yaffe, a neurologist at the Veterans Affairs Medical Center in San Francisco who wrote an editorial that accompanied the study. "But also the frustration over lack of effective interventions" for Alzheimer's.