Antioxidant Supplements and Foods for Preventing Dementia

Your brain is only about 2 percent of your body weight but may consume up to 50 percent of the oxygen you breathe, potentially releasing a firestorm of free radicals; yet, clinical studies of antioxidants like vitamin E for Alzheimer’s disease have not yielded cognitive benefits. In one trial, an antioxidant cocktail of vitamin C, vitamin E, alpha-lipoic acid, and coenzyme Q10 actually seemed to accelerate cognitive decline, making things worse compared to placebo.

In terms of prevention, long-term vitamin C supplement users don’t appear to be protected against developing dementia, though higher dietary intake of vitamin C does seem correlated with lower Alzheimer’s rates. But, that may just be a marker of eating a healthier diet, because a Mendelian randomization study found that life-long genetically-elevated vitamin C levels in the blood do not appear to affect Alzheimer’s disease risk. Perhaps this shouldn’t come as a surprise, though, since vitamin C doesn’t pass freely through the blood-brain barrier. It’s actively pumped from the bloodstream to achieve ten times the concentration in the brain. Brain levels may, therefore, not reflect blood levels, illustrated by brain preservation even in people literally dying from vitamin C deficiency (scurvy).

Vitamin C is just one of thousands of antioxidant compounds found in plants, some of which readily traverse the blood-brain barrier and may provide neuroprotective effects. The presence of fruit and vegetables phytochemicals in the cerebrospinal fluid surrounding the brain (obtained via spinal tap) is able to prove the brain accessibility of these compounds. In the Rush Memory and Aging Project, close to a thousand elderly men and women (average age 81) were followed for six years. In that time, those eating the most flavonols had a lower risk of developing Alzheimer’s disease. Sourced mostly in the American diet from tea, onions, and apples, flavonols appeared to halve the risk of developing Alzheimer’s within the subsequent six years comparing those who ate the most to those who ate the least). As with many nutrients in healthy foods, consumption was correlated with higher levels of education and exercise, but the study controlled for both these factors as well as other aspects of their diet and still found the apparent benefit.

The Framingham Offspring study is the most comprehensive and longest-running cohort to look into the question, following closer to two thousand men and women for a dozen years starting around age 60. While no relationship was found to age-related cognitive decline in general, flavonols were associated with a significantly lower risk of developing dementia. Those eating about two apples or two cups of tea worth of flavonols a day had a 46 percent lower chance of a dementia diagnosis compared to those getting less than one apple or tea’s worth. Particularly potent was a class of brain-accessing antioxidants called anthocyanins. Those averaging a single tablespoon of blueberries worth of anthocyanins a day had a 76 percent lower risk of dementia compared to those getting around less than ¾ of a teaspoon of daily blueberries worth. (Sadly, the number one source of anthocyanins for those in the study was not blueberries, but rather blueberry muffins).

Even just drinking fruit and vegetable juices may be beneficial. A study that followed over a thousand people for about six years found that people who drank fruit and vegetable juices regularly appeared to have a 76 percent lower risk of developing Alzheimer’s disease. The researchers suspect the active ingredient may have been the polyphenols. A systematic review and meta-analysis of randomized controlled trials that put to the test a variety of polyphenol-rich foods, beverages (such as green tea), or supplements found a significant boost in brain-derived neurotrophic factor, and improvement in a memory and concentration task, reaction time, and mental fatigue.

Beyond their antioxidant activity, some polyphenols have anti-inflammatory effects; polyphenols have been shown to protect nerve cells in vitro by inhibiting the formation of the amyloid plaques and tangles that characterize Alzheimer’s brain pathology. In theory, they could also “pull out iron” metals that accumulate in certain brain areas that may play a role in the development of Alzheimer’s and other neurodegenerative diseases.