Tall young men have a lower risk of developing dementia, according to a study of almost 700,000 males.

For every 2.5inches (6.5cm) in height above the average, risk of the memory-robbing disease reduced by 10 per cent.

This would mean men in England measuring 6ft (183cm) - above the average 5ft 9" (175.3cm) - have just over a 10 per cent less risk of dementia.

When the researchers compared men with their brothers, they found genetics only played a 'minor' role in the development of dementia.

Tall young men have a lower risk of developing dementia, according to a study

The team at the University of Copenhagen in Denmark studied 666,333 men who had entered National Service in the country.

All of the men were born between 1939 and 1959 and were followed in Danish nationwide registers until the age of 55 to 77 years old.

Height data was collected when the men were between the ages of 18 and 26 years, because height declines slightly as people age.

The study, published in eLIFE, found that 10,599 men developed dementia later in life.

Findings show that men born in 1939 with a height of 5ft 11" (181.5cm) had a 10 per cent lower risk of dementia than those with an average height of 5ft 9" (175cm).

The same was true for a second analysis of men born in 1959 - those who were 6ft 1" (185cm) tall had a 10 per cent lower risk compared with the average height of 5ft 10" (179cm).

In 2010, the Office for National Statistics said the average man in England was 5ft 9" (175.3cm) tall, BBC reported. This would mean those around 5ft 11" had a 10 per cent lower risk of dementia.

Adjustment for intelligence test scores and educational level - both of which are believed to give adults more resilience against cognitive decline - showed dementia risk was only slightly reduced.

Lead author Terese Sara Høj Jørgensen, assistant professor at the university, said: 'We wanted to see if body height in young men is associated with diagnosis of dementia, while exploring whether intelligence test scores, educational level, and underlying environmental and genetic factors shared by brothers explain the relationship.'

The participants involved 70,608 brothers and 7,388 twin brothers.

Height was still linked to dementia risk when the researchers examined brothers of different heights, with a 'minor' impact from genetics.

This suggests that genetics alone don't explain why shorter men had a greater dementia risk.

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The twin analysis showed similar, but imprecise estimates.

Study senior author Professor Merete Osler, of the University of Copenhagen said: 'Together, our results point to an association between taller body height in young men and a lower risk of dementia diagnosis later in life, which persists even when adjusted for educational level and intelligence test scores.'

She added: 'Our analysis of the data concerning brothers confirms these findings, and suggests the association may have common roots in early-life environmental exposures that are not related to family factors shared by brothers.'

The team were not able to explain their findings, which were only observational. But they posed some theories based on previous research.

Those who are taller have a higher level of growth hormone, that may play a role in preserving cognitive function.

This suggests growth in height may be an indicator of 'cognitive reserve' - a theory that some people have the ability to maintain their memory and IQ despite the impact of ageing.

Researchers don't know if the same findings can be applied to women as they were not included in the study.

Short height has been linked to development of dementia in a number of smaller studies.

Research in 2014 found that short people are up to 50 per cent more likely to die from dementia than the tallest.

The Alzheimer Scotland Dementia Research Centre at Edinburgh University analysed data from 18 studies involving almost 182,000 people between 1994 and 2008.

The height of participants was measured and other information, including social status and health history, collected.

Of 17,553 deaths during an average follow-up period of ten years, 1,093 were from dementia. The study found the risk of dying from dementia was 50 per cent higher among the shortest men compared with the tallest.

There was a 24 per cent increase in risk for every three inches of reduced height among those in the studies.

Researchers said the link between height and dementia was that a person's physical stature could capture 'a number of early life factors, including early-life illness, adversity, poor nutrition, and psychosocial stress.'

Dementia, of which Alzheimer's is the most common form, affects 850,000 people in the UK, according to the Alzheimer's Society.

Approximately 5.7million people are living with the illness in the US, the Alzheimer's Association says.