But that old adage "if it sounds too good to be true, it probably is" holds particularly true with these miracles of modern nutrition. Supplement manufacturers overload their pills with trace minerals, including harmful levels of metals that are linked to a wide variety of cognitive problems later in life, says Neal D. Barnard, MD, president of the Physicians Committee for Responsible Medicine and adjunct associate professor of medicine at George Washington School of Medicine. "These supplement manufacturers are focusing more on marketing than they are on health," he says. After all, it makes companies look good if they can advertise an entire day's nutrition in a single pill.
Dr. Barnard recently authored a report sounding the alarm on copper and iron in dietary supplements. His group analyzed levels of those metals in multivitamins from One a Day, Nature Made, and Centrum and found that the majority contained double the recommended amounts of copper and iron, much more than most people need. While both metals do provide health benefits—copper helps your body metabolize iron, boosts your immune system, and keeps your nerves and blood vessels healthy; iron carries oxygen to red blood cells and to muscles—too much can prove fatal to your brain health, says Dr. Barnard.
How? For one, the metals are increasingly being flagged as Alzheimer's disease triggers. In fact, the authors of an August 2013 study published in the Proceedings of the National Academy of Sciences concluded that copper appears to be one of the main environmental factors behind Alzheimer's disease. The researchers exposed mice then human brain cells to low levels of copper commonly seen in the average diet, and found that the metal interferes with the way the brain rids itself of the plaques that cause Alzheimer's disease. They also found that in mice already plagued with Alzheimer's, copper can pass the blood-brain barrier and accelerate the formation of plaques.
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Prior studies have come to similarly disturbing conclusions. In a 2010 review of the science on copper toxicity, published in Chemical Research in Toxicology, George Brewer, MD, professor emeritus of internal medicine and human genetics at the University of Michigan Medical School, wrote that research has linked both excess copper and iron to Alzheimer's disease, heart disease, diabetes, Parkinson's disease, and a few other neurological disorders.
He refers to one study in which researchers analyzed copper levels in the blood of a large sample of healthy adults over a six-year period, and those with the highest levels of copper lost cognition three times faster than adults with normal copper levels. Iron is suspected of causing similar damage, he writes, because both metals can introduce too much oxygen into the brain, causing "oxidative stress" that damages neurons. That same study noted that the people with the highest levels of copper and iron in their systems took multivitamins. A separate study, published in the 2008 Journal of Nutrition Health and Aging, found that in a group of 1,450 people, those who performed highest on cognition tests also had the lowest levels of copper and iron in their bloodstreams.
"Alzheimer's disease is an epidemic that is growing rapidly," says Dr. Barnard. "But up until now, most people had no idea they could do anything about it." People who take multivitamins are most likely overdosing on copper and iron, he adds. But certain processed foods are also beginning to play a role. Cereals and other goods fortified with copper and iron have disturbingly high levels, too, he says, and he's even written to the multivitamin manufacturers and some food companies asking them to remove the metals. "Not a single one has expressed any interest," he says.
How can you protect your brain against an onslaught of metals? Here's what Dr. Barnard recommends:
• Eat vegetables, not supplements. All meats and vegetables contain copper, Dr. Barnard says, but red meat contains forms of both copper and iron that are easily absorbed by your body, making it easy for the metals to accumulate over time and cause brain damage. Copper and iron in vegetables, on the other hand, are available in forms that are more easily regulated by your body—if you need more of either metal, your body takes what it needs from these plant sources and excretes the rest. Plus, eating less red meat will benefit your health—and the environment—in other ways. (For more foods that are good for your long-term brain health, read The Happiness Diet).
• Rethink all your supplements. Dr. Barnard says that most people who follow a diet of whole foods—lots of fruits, vegetables, and whole grains—don't need multivitamins, anyway. The only vitamins you might consider taking, he says, are vitamins B12 and D, which are both uncommon in foods. If your doctor does tell you to take a multivitamin, he adds, read labels to make sure you're taking on that's free of copper and iron.
• Buy a water filter. Eighty percent of homes in the U.S. have copper water pipes, and copper could be leaching from them. According to the National Sanitation Foundation, carbon filters, reverse osmosis systems, and distillers will remove copper from your water, so be sure to buy a filter that's NSF-certified to do just that.