Diet and Dementia: Eating Healthy in Midlife Doesn't Lower Alzheimer's Risk, Study Suggests

What a person eats in middle age doesn't affect their risk of developing dementia as they grow old, scientists believe. But experts suggested the findings aren't a green light to eat unhealthy foods, and emphasized what's good for the body is good for the brain.

Researchers studied 8,255 adults over a period of 25 years to document which participants developed the neurocognitive condition, and to identify any patterns in the foods they ate. The scientists published their findings in the journal JAMA.

The study is the latest attempt by scientists to gain a deeper understanding of dementia, a little-understood syndrome wherein a person's memory and ability to carry out everyday activities declines over time.

Some 50 million people across the world have dementia, with Alzheimer's the most common form of the disease. Vascular dementia and dementia with Lewy bodies are among its less common forms.

Experts aren't sure what causes the condition, or how to slow or treat it in most cases. As such, the authors said prevention is crucial, with something modifiable such as diet an ideal potential tool.

Past research has shown a link between diet and cognitive health, but those studies did not involve follow-ups with participants over long periods of time—the authors of the JAMA study said—and therefore didn't give an insight into the lengthy preclinical phase of dementia. The authors similarly took issue with studies linking specific nutrients to brain health, as the causes of dementia are complex.

In this new study, middle aged participants with an average age of 50 and healthy brains were recruited between 1991 and 1993. Of the 8,255 total, 344 participants had developed dementia in the 25 years following the start of the study.

At the launch of the study, the respondents completed questionnaires on what they ate, and twice more five and ten years later. Those with extreme diets, with very high calorie or very low calorie intakes, were excluded to avoid the results becoming skewed. The team used the resulting data to score how healthy the participants' diets were.

Those who ate a diet high in vegetables, fruit and fish were deemed healthy; while those who ate many fried, processed foods, as well as high fat dairy products and refined grains were categorized as consumers of the Western-type diet.

The authors concluded: "In this long-term prospective cohort study, diet quality assessed during midlife was not significantly associated with subsequent risk for dementia."

Dr. James Pickett, head of research at the charity Alzheimer's Society who was not involved in the research, commented: "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."

He advised ditching snacks like chips and substituting fruit, keeping active, and not smoking to not only cut the risk of heart disease, cancer and stroke, but also to keep the brain healthy.

Dr. Sara Imarisio, head of research at the charity Alzheimer's Research UK, who was not involved in the study, praised the authors for carrying out a study which looked at diet and dementia long-term.

"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," she said.

However, she warned: "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."