March 12, 2019

expert reaction to study on midlife diet and dementia risk

Research published in JAMA demonstrates that diet quality assessed during mid life was not significantly associated with subsequent risk for dementia.

Prof. Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“This report is based on a long-term study of British civil servants (the Whitehall Study). It is already well known that within this cohort there were marked differences in health according to their social position, with the higher grades of civil servants having better health and the lowest grades having the worst health. This report looks at the incidence of dementia in this cohort in relation to dietary intake measured using a questionnaire. The strength of the study is that it used multiple measures of food intake in the follow-up period. It has then used scores to classify the diets into a Western type diet or a Mediterranean type diet, even though the authors admit few people ate a Mediterranean diet. What we don’t know is anything about the nutritional quality of the diets and the linkage of dietary choice with other aspects of lifestyle such as smoking and alcohol intake both factors known to increase risk of dementia. A further limitation is that this study was conducted in civil servants who may not be representative of the general population.

“A more fundamental limitation is statistical over adjustment which removes factors through which diet may operate for example through raised blood pressure or diabetes which are linked to increased risk of cognitive function. Adopting a Mediterranean type diet would be predicted to reduce blood pressure and risk of type 2 diabetes. Consequently, it would be wrong to suggest that diet in middle-age is not important.”

Prof. Robert Howard, Professor of Old Age Psychiatry, University College London, said:

“Since we have no treatments to slow or stop progression of dementia, attention has understandably turned to ways in which we might prevent or delay dementia onset. Lifestyle interventions are popular candidates for this. The study provides convincing evidence that eating a good quality diet that is high in fruit and vegetables, whole grains and root vegetables and low in sugar, red and processed meat, trans fats and salt from midlife does not reduce later risk of cognitive decline or dementia. The results are disappointing because they remove a potential easily modifiable dementia risk factor from the table. This should not encourage people to follow poor dietary habits in midlife because obesity and diabetes are convincingly linked to higher dementia risk and the additional cardiovascular health benefits of a good diet are overwhelming.”

Prof. Clive Ballard, Professor of Age-Related Diseases, University of Exeter Medical School, said:

“This is a relatively small study, in a comparably young cohort with a very modest number of incident dementia cases. That means the statistical power of this study is very limited.

“Previous studies have shown there is a protective effect of being the right weight, rather than adhering to a specific diet.  Weight is a much more solid factor if both risk and protection of dementia than diet is.

“The strongest evidence to date is that there appears to be some protective benefit from eating a Mediterranean diet. This is much more specific than the diet used in this study and came from very specific cohorts of Greek Americans.

“Overall this is an underpowered study. It doesn’t directly contradict other studies, but it needs more studies and a meta analysis to have power to look at broader diet issues beyond weight.”

Dr James Pickett, Head of Research, Alzheimer’s Society, said:

“Dementia is one of the top ten causes of death, and the only one we can’t cure, prevent or even slowdown, which is why our researchers are hard at work to better understand what might cause dementia and how we can beat it.

“It’s estimated that up to a third of cases of dementia could be prevented by changes in lifestyle, including diet, so it’s surprising that this study suggests that diet in midlife does not have an impact on risk of dementia in later life. This was a robust study that followed participants over a long time but was based on self-reported feedback from the participants on their diet, which may not always be accurate.

“What we do know is that there are lots of factors which contribute to the development of dementia; some of which we can control. Ultimately, swapping those crisps for a fruit snack, staying active and not smoking can reduce your risk of heart disease, cancer and stroke, and is a good way to look after the health of your brain, too.”

Dr Sara Imarisio, Head of Research, Alzheimer’s Research UK, said:

“This is a well-conducted study that has looked at the long-term relationship between diet and dementia risk. As the diseases that cause dementia develop in the brain over decades, it is important that research into potential risk factors spans a similar time-frame.

“While observational studies like this are good at looking at links between lifestyle and dementia risk, looking at the effect of one lifestyle factor in isolation may not tell the whole story. This research doesn’t tell us whether a healthy diet might affect dementia risk in combination with other aspects of healthy living or for particular people with an increased risk of dementia.

“This research relied on people accurately self-reporting their eating habits and there can be a tendency for people to underestimate unhealthy behaviours in this kind of research. The study also based their results on diagnosis records which don’t reflect the full extent of dementia and often miss people who are in the mild stages.

“While the exact link between diet, brain resilience, cognitive decline and dementia remains unclear, healthy eating is associated with a number of other established dementia risk factors. The best current evidence suggests that controlling blood pressure and cholesterol, and maintaining a healthy weight alongside not smoking, drinking within the recommended limits, and staying mentally and physically active can all help us to maintain a healthy brain as we age.

“It’s important to identify the best approaches to encourage lifestyle change and promote healthy brain ageing to prevent dementia within at-risk populations. Alzheimer’s Research UK is now funding work looking at how we can encourage people at risk of dementia to adopt a Mediterranean-based diet in the hope it will reduce their dementia risk.”

‘Association of Midlife Diet with Subsequent Risk for Dementia’ by Akbaraly et al. was published in JAMA at 15:00 UK time on Tuesday 12 March 2019.

Declared interests

Prof. Tom Sanders: “Honorary Nutritional Director of HEART UK.  Scientific Governor of the British Nutrition Foundation.  He is now emeritus but when he was doing research at King’s College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks.  In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011.  This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London.  The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar.  Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.  Tom also used to work for Ajinomoto on aspartame about 8 years ago.  Tom was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain.  Tom has previously acted as a member of the Global Dairy Platform Scientific Advisory Panel and Tom is a member of the Programme Advisory Committee of the Malaysian Palm Oil Board.  In the past Tom has acted as a consultant to Archer Daniel Midland Company and received honoraria for meetings sponsored by Unilever PLC.  Tom’s research on fats was funded by Public Health England/Food Standards Agency.”

Prof. Robert Howard: “I have no conflicts of interest.”

Dr Sara Imariso: “no conflicts to declare”

None others received.