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Nutritional supplements and cognitive ageing

When it comes to brain health, can you tell your omega-3 from your vitamin D? As part of our Staying Sharp series, Professor David Smith of the University of Oxford looks at the evidence on links between dietary supplements and thinking skills as we age.

My advice

  • Stick to a good diet, with 5-a-day of fruit (especially berries) and veg; eat fish.
  • Keep your sugar intake down.
  • If you’re over 50, consider supplementing your diet with fish oil and vitamins B12 and D.
  • Be aware that certain drugs (metformin, proton pump inhibitors) can reduce absorption of B12, so you may need to talk to your doctor about taking a supplement.

A good diet matters

There is good evidence to say that dietary patterns are important to maintain good thinking skills, or cognitive function, as other sections in these web pages describe.

It is more difficult to make recommendations about nutritional supplements – sometimes known as dietary supplements – such as vitamins, minerals and other substances that we take to add to the nutrition provided by the food we eat. This is because the need for supplements is related to the levels of the nutrients in the body, which in turn is determined by your overall diet.

To supplement or not to supplement?

If your diet is very good, your levels of nutrients will probably be close to optimal and so adding extra through taking supplements will make no difference.

However, as we age, many of us no longer absorb nutrients from food via our digestive system as efficiently as we did when we were younger. So, even if we eat a very good diet, our body may have inadequate levels of certain nutrients. 

A common problem is that the stomach shrinks in older age and no longer produces enough acid to liberate nutrients from food. Also, the enzymes in the intestine that work on freeing nutrients from food and helping them to be absorbed into the body through the wall of the gut may not be as active as they once were.

Nutrients whose absorption is reduced in older age include vitamin B12, folate (vitamin B9), calcium, and iron. But it may not help much to take a multivitamin pill since the amounts of vitamins in these pills are about, or below, the recommended daily allowance which you are probably getting from your food anyway if you are eating a good diet. To overcome poor absorption, considerably larger amounts are often needed – especially for vitamin B12. Such amounts of folate and B12 are often added to breakfast cereals.

Folate and folic acid explained

Vitamin B9 is known as 'folate' in its natural form and 'folic acid' in its synthetic form. It's the folic acid form that's used in dietary supplements and foods.

Nutrients, brain health and ageing

Our research in Oxford found that, in normal older people, the level of vitamin B12 in the blood is related to the rate at which the brain shrinks. It’s well known that the brain shrinks somewhat as we grow older, but people with low to normal levels of vitamin B12 showed more rapid shrinkage.

We found that people with mild cognitive impairment benefitted greatly from a B vitamin mixture (folic acid, vitamins B6 and B12): the rate of brain shrinkage was much reduced and their cognitive decline was markedly slowed. The main vitamin turned out to be B12 (0.5 mg per day).

Fish oils contain the essential polyunsaturated fatty acids called ‘omega-3’. Omega-3 fatty acids may protect the brain, for example from shrinking and perhaps from cognitive decline. In Oxford, we have found that the beneficial effects of B vitamins on the brain are enhanced in people with good omega-3 status.

Our usual diet does not contain enough omega-3 and we need to eat fish at least once a week to get this nutrient. Even then, we may not get enough so an intake of between 1 and 2 g per day of total omega-3 from fish oil capsules is my recommendation. For vegetarians and vegans, there are capsules that contain omega-3 from algae.

Fish fact

Salmon, mackerel, herring and fresh tuna are particularly good sources of omega-3.

Vitamin D is formed by the action of UV light on the skin, but most of us do not get enough sun when we age. It is important to take supplements of vitamin D to protect your bones, but also to protect the brain. My view is that we should take 20-40 micrograms per day of vitamin D3.

You may have heard about a possible role for other types of nutrients in brain health – for example, antioxidants, flavonoids and other vitamins such as C and E.

However, there isn’t sufficient evidence at the moment to indicate whether, taken in the form of supplements, they might help protect our thinking skills in ageing.

Take advice

Nutritional supplements in large amounts can have side-effects. If you have any concerns or questions about taking supplements, please discuss them with your doctor.

About the author

Professor David Smith is Professor Emeritus of Pharmacology at the University of Oxford and a co-founder of the Oxford Project to Investigate Memory and Aging (OPTIMA), which he directed for 20 years. His current research is on the prevention of Alzheimer’s disease.

Key references

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Last updated: Jan 16 2024

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