Scientists have suggested eating very little sugar up to the age of two may help protect the brain decades later.
The research analysed the impact of the end of sugar rationing in the UK which led to a rapid increase in the amount of sugar in people's diets.
The results suggest those who were toddlers during sugar rationing had a 23% lower risk of dementia.
The study cannot provide definitive proof, but experts say a healthy diet is good for the brain anyway.
This is not the first study to suggest the first 1,000 days of life are critically important for our future health.
A suite of studies have been looking at the "natural experiment" of the UK recovering from World War Two and the end of food rationing.
When sugar rationing concluded in September 1953, average sugar consumption was estimated to go from around 41g a day (10 sugar cubes) to 80g (20 sugar cubes) almost immediately.
Previous research linked this to an increase in type 2 diabetes and blood pressure years later.
Women with their ration books at London's Petticoat Lane Market during World War Two.
The latest study looked at nearly 65,000 people taking part in the UK BioBank project.
The analysis - by the Hong Kong University of Science and Technology in Guangzhou, China - looked at children growing up either side of sugar rationing.
They argued sugar rationing up to the age of two was linked to a 23% lower level of dementia and the disease being diagnosed two-and-a-half years later.
"Our findings suggest that limiting sugar during the earliest stages of life may have lasting benefits for brain health," said researcher Jiazhen Zheng.
The data was published in the journal Neurology.
But Zheng said "further research is needed" to understand whether sugar was having this effect.
Veg on a stick - a wartime snack in 1941
"They may be onto something," said Rachel Richardson, the methods support unit lead for evidence production and methods directorate at Cochrane, an independent non-profit network that gathers and summarises medical research.
However, she said this "does not represent a smoking gun" linking early sugar intake to dementia.
One big issue is, it is impossible to know how much sugar each of the people in the study were actually eating, merely when they were born relative to sugar rationing.
"This evidence relates to people born in the 1940s and 1950s and so its applicability to young children today is limited - for example, weaning took place earlier and this would have a large impact on the early nutrition of babies and children," said Richardson.
Prof Ian Maidment, professor of clinical pharmacy at Aston University, said: "It is an interesting idea, it helps inform debate, but in my opinion we need more evidence."
He said connecting "something that happened 80 years ago" and projecting that onto health now meant there were "loads" of other factors that could be playing a role.
Dr Sara Rodrigues, from Alzheimer's Research UK, said: "It's important to remember that this was an observational study.
"This means it can identify links between diet and dementia risk, but it cannot prove that eating less sugar directly prevents dementia.
"Eating a healthy, balanced diet is one of the best ways to support your brain health and it's never too late to make positive changes."
