- Iron is important at all ages, and it seems clear now that iron deficiency can affect cognition long before anemia is diagnosed. However, too much iron may also increase Alzheimer's risk, so you need to steer a middle road.
- Magnesium and zinc also seem to be important minerals for cognition, and zinc deficiency has been linked to Alzheimer's.
- B vitamins, especially B12 and folate, are important to fight age-related cognitive impairment and Alzheimer's.
- Vitamins C, D, and E, are probably also important in this fight.
- Interactions need to be taken into consideration. Zinc may impact iron absorption; vitamin C may not be well absorbed if iron is not bound; the vitamins are more effective if omega-3 levels are high.
Let me start by saying that if you're healthy and are eating a good balanced diet, there should be no need for you to take supplements. I also want to emphasize that the best way of meeting your body's needs for certain vitamins and minerals is to get them from food. In some cases, for one reason or another, this may not be possible. For example, as a (mostly) vegan, I take iron and B12 supplements, to make up for these deficiencies in my diet. Elderly adults with small appetites may also find it hard to get all the nutrients they need from their diet.
What nutrients are important for brain health and cognition?
Number one mineral for cognition, that goes right across the age groups, is iron. A number of studies have found that iron deficiency in children and adolescents is associated with lower scores of cognitive tests, and indeed, it may be that iron deficiency during infancy has long lasting effects on cognition. The effects on adults have been less studied, but there is some evidence that iron deficiency may be linked to poorer attention. What's worth noting is that the levels at which iron is "deficient" may be overstated. It now seems that negative effects occur long before a person is officially diagnosed with anemia.
Other minerals that may impact learning and memory are magnesium and zinc, although evidence is limited thus far. Magnesium deficits are common in industrialized countries, and increase with age. Vegetarians, adolescents, and older adults, are particularly at risk of zinc deficiency. An analysis of Alzheimer's has revealed that one type of the disease, which is found most commonly at a younger age (50- to early 70s) and typically shows itself first in language and number difficulties, is associated with a significant zinc deficiency.
Good sources of magnesium are dark green leafy vegetables, some nuts (especially almonds and cashews), beans, seeds and whole unrefined grains (especially buckwheat). Red meats, fish and grains are good sources of zinc.
Do bear in mind that it is not a case of "if some is good, more is better"! Having too much is not a good idea either; this is another reason why getting your vitamins and minerals from food rather than supplements is a good idea. Too much iron, in particular, has been linked to an increased risk of Alzheimer's. It has been argued that many neurodegenerative diseases are partly caused by poorly bound iron, and it is vital to consume nutrients which bind iron, such as brightly-colored fruits (especially purple) and vegetables — but not, perhaps, green tea, which does bind iron, but taking them at the same time seems to cancel out each other's benefits!
Just to complicate the matter further, there is evidence that zinc inhibits iron absorption. These complications suggest there is something in the idea that you need to consider food combinations.
Vitamins B, C, D, and E all seem to be important for cognition, mainly in relation to prenatal development and prevention of Alzheimer's and age-related cognitive impairment. A long-running study of older adults found that those with diets high in omega 3 fatty acids and in vitamins C, D, E and the B vitamins had higher scores on cognitive tests than people with diets low in those nutrients, and moreover that these were dose-dependent, with each standard deviation increase in the vitamin BCDE score ssociated with an increase in cognitive score. Additionally, they showed less brain shrinkage than those with lower intakes of these nutrients.
The B vitamins are often called the B-complex vitamins, and they are a messy sort of group. The main ones of interest for cognition are B12, folate, and choline. Again, most of the research has focused on prenatal development, and age-related cognitive impairment and dementia.
The importance of folate and B12 has a lot to do with homocysteine, which is produced in the body by the breakdown of a dietary protein called methionine. High levels of homocysteine have been linked to increased risk of Alzheimer's, stroke, and vascular dementia, and greater brain shrinkage. B-vitamins are required to convert homocysteine back to methionine, and high levels of homocysteine go hand in hand with low levels of B12 and folate. Diet isn't the only reason for increased levels of homocysteine; smoking has also been implicated. But the association between homocysteine and age-related cognitive decline is not straightforward — it appears that seniors with normal levels of vitamin B12 perform better if their folate levels are high, but when vitamin B12 is low, high levels of folate were associated with poor cognitive performance, as well as a greater probability of anemia. Vitamin B12 is often deficient in older people.
There is also some evidence that B12 is more effective in slowing cognitive decline if levels of omega-3 oils are high.
Folate is a water-soluble B vitamin found particularly in citrus fruit, green leafy vegetables, whole-wheat bread, water-soluble dried beans and peas; however, they are often destroyed by cooking or processing. In the United States, Canada and Australia, flour is fortified with folic acid. Vitamin B12 is naturally found in animal foods including fish, milk and milk products, eggs, meat, and poultry.
Among older adults, choline, particularly in conjunction with omega-3 fatty acids and uridine (not available from food), has been found to improve memory in those cognitively impaired. Top sources of choline are eggs, peanuts, and meat. Fish and soy are also good sources.