Lately there have been many reports in the popular press discussing the association between the accumulation of the mineral iron in the brain, and Alzheimer's Disease. This is excellent work and its exciting because it may result in a relatively easy way to identify changes in the brain even before there are cognitive symptoms.
But, before you give up valuable foods containing iron in your diet, think again. Iron is absolutely essential for brain function - it transports oxygen for energy production allowing brain cells to function, is involved in making neurotransmitters and in their everyday activity, and is vital for the production of myelin which surrounds neurones (the loss of which causes Multiple Sclerosis).
The problem with iron is the result of things going wrong in the regulation of iron levels inside the brain, not a result of what you eat.
I've had a good look at the research in this area to reassure myself. Even neuroscientists don't yet understand everything about of how iron is regulated in the brain - iron metabolism is immensely complex and the way it is dealt with in the body generally (outside the blood brain barrier) is not necessarily the same as what happens inside the brain itself.
One thing that supports the distinction is that there are some people with inborn errors of metabolism - haemachromatosis and thalassaemias - who have excessively high levels of iron in their blood and some body tissues, requiring medical intervention to avoid long term damage: these people do not have elevated levels of iron in their brains, nor are they more likely to experience neurodegeneration than people who have normal body iron levels.
The amount of iron you eat does affect the levels in your blood and your body, but not in the brain it seems. Something goes wrong with the way iron is dealt with in the brain and that affects the levels there.
There are a number of ways ageing and lifestyle factors might contribute to these elevated iron levels inside the brain but the most likely culprit is inflammation, or to be more precise, neuroinflammation, meaning it is happening inside the brain. I write a lot more about how the brain works, about inflammation and neuroinflammation and what to eat and do to reduce it in Eat To Cheat Dementia and Better Brain Food - I urge you to read more there.
In summary, it seems that neuroinflammation is the both the cause and the result of iron accumulation in brain cells. Its really not clear which comes first yet - it may be that age-related changes in the blood brain barrier could allow substances into the brain which increase inflammation there; there may be some, as yet undiscovered factor, which causes a change in the way iron is dealt with in the brain. What we do know is that neuroinflammation seems to contribute to accumulation of iron in neurones and the glia (cells inside the brain which support neurones and have a wide range of functions). This in turn accelerates inflammation and might create a vicious cycle.
In ageing, iron deficiency anaemia (low levels of iron in the blood and body) is quite common and hinders both physical and cognitive health. There is not much research that has looked at the impact of diet on brain iron levels, but what there is doesn't link what's eaten with brain iron accumulation. Some work suggests that iron, taken in tablet form, or as a liquid supplement might be an issue, but that food sources are not - the body deals with food better than supplements, not surprisingly.
Certainly, for anyone with a diagnosed deficiency of iron, supplements to reverse the deficiency are essential. But for anyone else, iron supplements are best avoided.
Eat and enjoy good iron-containing foods for your body and your brain: the 'haem' type in meats, eggs and fish is especially useful, forming a vital part of an otherwise predominantly plant-based diet for healthy ageing. Non animal sources of iron include pulses and dark green leafy vegetables. You can read more on the individual nutrients essential for healthy ageing in Eat To Cheat Ageing.