Diet - The evidence base

A healthy diet may boost brain health.

Evidence is emerging that a healthy diet that includes antioxidants, unsaturated fats and certain vitamins may help reduce your risk of dementia.  These nutrients are known to be important for maintaining healthy brain cells.  The research to date is not conclusive, but suggests they may also play a role in reducing dementia risk.

We know that a healthy diet can reduce your risk of heart disease and some cancers.  Keeping your brain functioning well is another good reason to enjoy a healthy diet.

While eating well cannot guarantee you won’t develop dementia, the existing evidence points to an important role in reducing your risk and maintaining the health of your brain.

Evidence rating for diet

For most of the nutrients suggested to influence dementia risk, results of observational studies and intervention trials are inconclusive.

The most consistent evidence is for beneficial effects of higher fruit and vegetable consumption and the Mediterranean diet, but further research is needed.

A healthy, low fat, high fruit and vegetable diet is of course good for cardiovascular health, so there’s every reason to expect it can benefit brain health as well.

What’s the evidence that diet affects dementia risk?

We don’t have all the answers, but there is growing evidence that regular intake of certain nutrients and foods, while avoiding others, can help keep your brain healthy and may reduce your risk of developing dementia.

Several nutrients, and particular diets, have been linked to maintaining healthy brain cells and reducing dementia risk.  The available evidence for these and how they might reduce dementia risk is explained below.


Various nutrients are known to have antioxidant effects, and we are still discovering others.

Vitamins C and E have antioxidant effects.  Some studies have found that people with higher intakes of these have, on average, a lower risk of developing dementia.  However, more recent large intervention studies have failed to find any protective effect.  So increasing your intake of vitamin C or E to reduce dementia risk is not recommended.

Other antioxidants include polyphenols and flavanoids found in fruits and vegetables.  Recent studies are finding an association between higher intakes of these and a lower risk of dementia.  Randomised intervention trials have not yet been conducted for these antioxidant nutrients.  More research is needed, but increasing your intake of fruits and vegetables has other health benefits so there is no need to delay this dietary change.

Antioxidants help to prevent oxidation, a process that damages our cells, including brain cells.  Oxidation occurs in Alzheimer’s and other diseases that cause dementia.

B group vitamins

Folate (vitamin B9) and vitamin B12 are necessary for cell function.  Deficiencies have been associated with cognitive impairment and dementia.  However, it has not been proven that B12 or folate supplementation reduces the risk of developing dementia.  Until we have further evidence it is recommended to include folate and B12 in your diet and check for and treat any deficiencies of these vitamins.  You should always first discuss supplement use with your doctor.

In the US, flour products have been fortified with folate since 1998.  A US study found that high folate levels protected against cognitive decline, but only in those with normal vitamin B12 levels (Morris MS, et al. Am J Clin Nutr 2007;85:193-200).  Those with low B12 and high folate were 5 times more likely to show cognitive impairment.  So folate supplementation should not be started before checking for vitamin B12 deficiency.

Vitamin B12 and folate deficiencies are associated with elevated homocysteine levels, which is associated with an increased risk of developing of dementia.  In one study of over 1,000 people, higher homocysteine levels were associated with double the risk of developing Alzheimer’s disease (Seshadri S, et al. N Engl J Med, 2002; 356:476-483).  Homocysteine is an amino acid.

Dietary fats

A high intake of saturated fat has been associated with increased risk of developing dementia.  However, moderate to high intakes of monounsaturated and polyunsaturated fats have been associated with reduced risk for dementia.

In one study, moderate intake of unsaturated fats at midlife reduced the risk of dementia in late life by around half.  Moderate saturated fat intake approximately doubled the risk (Laitinen MH, et al Dement Geriatr Cogn Disord, 2006; 22:99-107)

Although more studies are needed, reducing excess saturated fat and including moderate amounts of unsaturated fats has other health benefits.  So there is no need to delay this dietary change.

Increasing omega-3 fatty acids (found in fish and some other foods) to reduce dementia risk has received support following some studies suggesting this was protective.  However, recent randomised trials of omega-3 supplements to prevent dementia have failed to show any reduction of risk (ref).

There is currently insufficient evidence to support a high omega-3 diet or use of omega-3 supplements to reduce dementia risk.

The Mediterranean diet

Higher adherence to the Mediterranean diet has been found to be associated with a lower risk of cognitive decline and dementia.  The traditional Mediterranean diet is low in saturated fat and high in antioxidants.  It includes:

  • lots of fruit, vegetables and legumes
  • lots of fish
  • olive oil
  • not a lot of meat


Next ...... the guidelines to help you enjoy a brain-heart healthy diet




Call the National Dementia Helpline on 1800 100 500 for questions, information, advice.


Your Brain Matters was supported by funding from the Australian Government under the Chronic Disease Prevention and Service Improvement Fund from July 2012 to June 2015.



Dementia Australia would like to acknowledge the Aboriginal people as the traditional custodians and carers of the country of Australia.